Shift register and image display apparatus using the same

[0001] The present invention relates to a shift register which can be favorably used for, for example, a driving circuit of an image display apparatus and can shift an input pulse even when a clock signal is smaller in an amplitude than a driving voltage, and further concerns an image display apparatus using the same.

[0002] For instance, in a data signal line driving circuit and a scanning signal line driving circuit of an image display apparatus, a shift register has been widely used to adjust timing when sampling each data signal from an image signal, and to generate a scanning signal applied to each scanning signal line.

[0003] Meanwhile, the power consumption of an electronic circuit increases proportionally to a frequency, a load capacity, and the square of a voltage. Thus, a driving voltage has been set lower to reduce power consumption in a circuit connected to an image display apparatus, for example, in a circuit for generating an image signal transmitted to the image display apparatus, or in the image display apparatus itself.

[0004] Regarding a circuit using a polycrystalline silicon thin film transistor to secure a large display area, for example, in a pixel, a data signal line driving circuit, and a scanning signal line driving circuit, a driving voltage is not sufficiently reduced because a difference in a threshold voltage sometimes reaches about several V between substrates or on a single substrate. However, in a circuit using a monocrystalline silicon transistor such as the circuit for generating an image signal, a driving voltage is set at a value such as 5 V, 3.3 V, or a smaller value in many cases. Hence, when applying a clock signal lower than a driving voltage of the shift resistor, the shift register is provided with a level shifter for raising a voltage of the clock signal.

[0005] To be specific, as shown in FIG. 39, when a clock signal CK having an amplitude of about 5 V is applied to a conventional shift resistor 101, a level shifter 103 increases a voltage of the clock signal CK to a driving voltage (15 V) of the shift resistor 101. The clock signal CK whose voltage has been increased is then applied to flip flops F₁ to F_n, and a shift resistor section 102 shifts a start signal SP in synchronization with the clock signal CK.

[0006] However, in the conventional shift register 101, the clock signal CK is level-shifted before being transmitted to the flip flops F₁ to F_n. Therefore, the longer a distance between the ends of the flip flops F₁ to F_n, the longer a distance for transmission, resulting in larger power consumption.

[0007] To be specific, the capacity of a signal line for transmission increases with a transmitting distance. Thus, the level shifter 103 requires a larger driving capability, thereby increasing power consumption. Further, as in the construction in which the polycrystalline silicon thin film transistor is used to form the driving circuit including the level shifter 103, when the driving capability of the level shifter 103 is not sufficient, it is necessary to provide a buffer 104 between the level shifter 103 and the flip flops F₁ to F_n as indicated by a dotted line of the FIG. 39 to transmit a waveform without deformation. Consequently, larger power consumption is necessary.

[0008] In recent years, an image display apparatus with a larger display screen and a higher resolution has been demanded, so that more steps have been required for the shift resistor section 102. Therefore, there has been an increasing need for a shift register and an image display apparatus that can achieve small power consumption even in the case of a large distance between the ends of the flip flops F₁ to F_n.

[0009] In order to solve the aforementioned problem, a shift register of the present invention includes flip flops of a plurality of steps that operate in synchronization with a clock signal, and level shifters for increasing a voltage of a clock signal smaller in an amplitude than a driving voltage of the flip flop and for applying the clock signal to each of the flip flops, the shift register for transmitting an input pulse in synchronization with the clock signal being characterized by including the following means.

[0010] Namely, the flip flops are divided into a plurality of blocks, each including at least one flip flop. The level shifters are respectively provided in the blocks. Among a plurality of the level shifters, at least one of the level shifters, which correspond to the blocks requiring no clock signal input for transmitting the input pulse, is suspended at that point.

[0011] Here, the flip flops constituting the shift register determine whether a clock signal is necessary or not for transmitting an input pulse in each of the blocks. For instance, when set reset flip flops are used as the flip flops, between a pulse input to a block and a setting of the flip flop of the final step, the block needs a clock signal. Meanwhile, when D flip flops are used as the flip flops, between a pulse input to a block and the end of a pulse output of the flip flop of the final step, the block needs a clock signal. Additionally, in any one of the cases, a construction is acceptable in which each of the blocks includes a single flip flop and the level shifter is provided for each of the flip flops or for a plurality of the flip flops.

[0012] According to the above arrangement, a voltage of a clock signal is increased in any one of a plurality of the level shifters and is applied to the flip flops in the block corresponding to the level shifters, and input pulses are transmitted in order in synchronization with the clock signal whose voltage has been increased. Furthermore, among the level shifters, at least one of them requiring no clock signal output is suspended.

[0013] Here, a block requiring no clock signal is, for example, a block transmitting no input pulse. Moreover, even in the case of a block transmitting an input pulse, when the flip flop is the set reset flip flop, which is set in response to a clock signal and is reset in response to an output of the following flip flop, a clock signal is not necessary after the flip flop of the final step is set.

[0014] According to the above arrangement, the shift register is provided with a plurality of the level shifters. Therefore, as compared with a construction in which a single level shifter applies a level-shifted clock signal to all flip flops, it is possible to reduce a distance between the level shifter and the flip flop. Consequently, a distance for transmitting a level-shifted clock signal can be reduced so as to cut a load capacity of the level shifter and to reduce the need for a large driving capability of the level shifter. Even when the driving capability is small and a distance is long between the ends of the flip flop, this arrangement makes it possible to eliminate the need for a buffer between the level shifter and the flip flops, thereby reducing power consumption of the shift register. Additionally, at least one of a plurality of the level shifters suspends its operation; thus, as compared with a construction in which all the level shifters are simultaneously operated, the power consumption of the shift register can be smaller. According to the above results, it is possible to achieve the shift register which can be operated by a clock signal input at a low voltage with small power consumption.

[0015] For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.

[0016] FIG. 1 is a block diagram showing a main construction of a shift register including set reset flip flops in accordance with one embodiment of the present invention.

[0017] FIG. 2 is a block diagram showing a main construction of an image display apparatus using the shift register.

[0018] FIG. 3 is a circuit diagram showing an example of a pixel in the image display apparatus.

[0019] FIG. 4 is a timing chart showing an operation of the shift register.

[0020] FIG. 5 is a circuit diagram showing an example of the set reset flip flop used in the shift register.

[0021] FIG. 6 is a timing chart showing an operation of the set reset flip flop.

[0022] FIG. 7 is a circuit diagram indicating an example of the level shifter.

[0023] FIG. 8 is a block diagram showing a main construction of the shift register including D flip flops in accordance with another embodiment of the present invention.

[0024] FIG. 9 is a timing chart showing an operation of the shift register.

[0025] FIG. 10 is a circuit diagram showing an example of the D flip flop.

[0026] FIG. 11 is a timing chart showing an operation of the D flip flop.

[0027] FIG. 12 is a circuit diagram showing an example of an OR circuit used in the shift register.

[0028] FIG. 13 is a block diagram showing a variation of the shift register.

[0029] FIG. 14 is a circuit diagram showing an example of the level shifter in the shift register.

[0030] FIG. 15 is a block diagram showing a shift register in which a level shifter is provided for a plurality of set reset flip flops, in accordance with still another embodiment of the present invention.

[0031] FIG. 16 is a circuit diagram showing an example of an OR circuit used in the shift register.

[0032] FIG. 17 is a timing chart showing an operation of the shift register.

[0033] FIG. 18 is a block diagram showing a variation of the shift register.

[0034] FIG. 19 is a circuit diagram showing an example of the level shifter in the shift register.

[0035] FIG. 20 is a block diagram showing a shift register in which a level shifter is provided for a plurality of D flip flops, in accordance with still another embodiment of the present invention.

[0036] FIG. 21 is a circuit diagram showing an example of an OR circuit used in the shift register.

[0037] FIG. 22 is a timing chart showing an operation of the shift register.

[0038] FIG. 23 is a block diagram showing a variation of the shift register.

[0039] FIG. 24 is a circuit diagram showing an example of the level shifter in the shift register.

[0040] FIG. 25 is a block diagram showing a shift register including a latch circuit for controlling an operation of the level shifter, and set reset flip flops, in accordance with still another embodiment of the present invention.

[0041] FIG. 26 is a block diagram showing an example of the latch circuit.

[0042] FIG. 27 is a timing chart showing an operation of the shift register.

[0043] FIG. 28 is a block diagram showing another example of the latch circuit.

[0044] FIG. 29 is a timing chart showing an operation of the latch circuit.

[0045] FIG. 30 is a block diagram showing a shift register including the latch circuit and D flip flops, in accordance with still another embodiment of the present invention.

[0046] FIG. 31 is a block diagram showing an example of the latch circuit.

[0047] FIG. 32 is a timing chart showing an operation of the shift register.

[0048] FIG. 33 is a block diagram showing another example of the latch circuit.

[0049] FIG. 34 is a timing chart showing an operation of the latch circuit.

[0050] FIG. 35 is a circuit diagram showing a clock signal control circuit which is provided when the level shifter of each block selectively applies a clock signal to the D flip flop in the block, in accordance with still another embodiment of the present invention.

[0051] FIG. 36 is a block diagram showing a main part of a shift register in accordance with still another embodiment of the present invention.

[0052] FIG. 37 is a timing chart showing an operation of the shift register.

[0053] FIG. 38 is a circuit diagram showing a voltage-driven level shifter in accordance with a variation of the present invention.

[0054] FIG. 39 is a block diagram showing a shift register including a level shifter in accordance with a conventional art.

[0055] Embodiment 1

[0056] Referring to FIGS. 1 to 7, the following explanation describes one embodiment of the present invention. Here, the present invention can be widely adopted for a shift resistor, in which an inputted clock signal is smaller in an amplitude than a driving voltage. The following describes the present invention adopted for an image display apparatus as a suitable example.

[0057] To be specific, as shown in FIG. 2, an image apparatus device 1 of the present embodiment is provided with a display section 2 having pixels PIX in a matrix form, a data signal line driving circuit 3 and a scanning signal line driving circuit 4 that drive the pixels PIX. When a control circuit 5 generates an image signal DAT for indicating a display state of the pixels PIX, the image display apparatus 1 displays an image in response to the image signal DAT.

[0058] The display section 2 and the driving circuits 3 and 4 are disposed on a single substrate to reduce the manufacturing steps and the wiring capacity. Moreover, in order to integrate more pixels PIX and to increase a display area, the circuits 2 to 4 consist of polycrystalline silicon thin film transistors formed on a glass substrate. Furthermore, when a normal glass substrate (glass substrate having a deformation point of 600 C. or less) is used, in order to prevent warp and deformation appearing in a process performed at a deformation point or more, the polycrystalline silicon thin film transistor is manufactured at a process temperature of 600 C. or less.

[0059] Here, the display section 2 is provided with 1 pieces (hereinafter, a capital letter L is used for convenience of reference) of data signal lines SL₁ to SL_L and m pieces of scanning signal lines GL₁ to GL_m respectively intersecting the data signal lines SL₁ to SL_L. Here, i represents any one of positive integers of L or less and j represents any one of positive integers of m or less. A pixel PIX_(i,j) is provided for each combination of the data signal line SL₁ and the scanning signal line GL_j. Namely, each of the pixels PIX_(i,j) is disposed in a part surrounded by two adjacent data signal lines SL_iSL_i1 and two adjacent scanning lines GL_jGL_j1.

[0060] Here, as shown in FIG. 3, the pixel PIX_(i,j) is provided with a field-effect transistor (switching element) SW, in which a gate is connected to the scanning line GL_j and a drain is connected to the data signal line SL_i, and a pixel capacity C_P in which one of electrodes is connected to a source of the field-effect transistor SW. Further, the other end of the pixel capacity C_P is connected to a common electrode line which is used in common for all the pixels PIX. The pixel capacity C_P consists of a liquid crystal capacity C_L and a secondary capacity C_S, which is added if necessary.

[0061] When the scanning line GL_j is selected in the pixel PIX_(i,j), the field-effect transistor SW is brought into conduction, and voltage applied to the data signal line SL_i is applied to the pixel capacity C_P. On the other hand, while the field-effect transistor SW is shut off after the selection period of the scanning signal line GL_j, the pixel capacity C_P maintains a voltage applied at the time of shutting off. Here, transmittance and reflectance of liquid crystal vary in accordance with a voltage applied to the liquid capacity C_L. Therefore, the scanning signal line GL_j is selected and voltage is applied to the data signal line SL_i in accordance with image data, so that it is possible to vary a display state of the pixel PIX_(i,j) in accordance with the image data.

[0062] In the image display apparatus 1 of FIG. 2, the scanning signal line driving circuit 4 selects the scanning signal line GL, and image data, which is transmitted to the pixels PIX so as to correspond to a combination of the selected scanning signal line GL and the data signal line SL, is outputted to each of the data signal lines SL by the data signal line driving circuit 3. With this arrangement, the image data is respectively written to the pixels PIX connected to the scanning signal line GL. Further, the scanning signal line driving circuit 4 successively selects the scanning signal lines GL, and the data signal line driving circuit 3 outputs the image data to the data signal lines SL. Consequently, the image data is respectively written to all the pixels PIX on the display section 2.

[0063] Here, between the control circuit 5 and the data signal line driving circuit 3, image data to the pixels PIX is transmitted as an image signal DAT on a time division. The data signal line driving circuit 3 extracts image data from the image signal DAT at the timing based on a clock signal CKS and a start signal SPS that serve as timing signals with predetermined periods.

[0064] To be specific, the data signal line driving circuit 3 is provided with a) a shift resistor 3a which successively shifts the start signals SPS in synchronization with the clock signals CKS so as to generate output signals S₁ to S_L, each being shifted in timing by a predetermined interval; and b) a sampling section 3b which samples the image signal DAT at a timing indicated by each of the output signals S₁ to S_L and extracts image data to be outputted to each of the data signal lines SL₁ to SL_L, from the image signal DAT. In the same manner, the scanning signal line driving circuit 4 is provided with a shift resistor 4a which successively shifts the start signals SPG in synchronization with the clock signals CKG so as to output scanning signals, each being shifted in timing by a predetermined interval, to the scanning signal lines GL₁ to GL_m.

[0065] Additionally, in the image display apparatus 1 of the present embodiment, the display section 2, the driving circuits 3 and 4 are formed by polycrystalline silicon thin film transistors. Each of these circuits 2 to 4 has a driving voltage Vcc of, for example, about 15 V. Meanwhile, the control circuit 5 is formed by a monocrystalline silicon transistor on a different substrate separately from the circuits 2 to 4. A driving voltage of the control circuit 5 is set at a value smaller than the driving voltage Vcc, for example, 5 V or less. Additionally, the circuits 2 to 4 and the control circuit 5 are formed on the different substrates; however, the number of signals transmitted between the circuits 2 to 4 and the circuit 5 is considerably smaller than that of signals transmitted among the circuits 2 to 4. For example, the image signal DAT, the start signals SPS (SPG), and the clock signal CKS (CKG) are included at most. Further, the control circuit 5 is formed by a monocrystalline silicon transistor, so that a sufficient driving capacity can be secured with ease. For this reason, even in the case of formation on different substrates, it is possible to suppress an increase in the manufacturing steps, a wiring capacity, and power consumption, to a degree causing no serious problem.

[0066] Additionally, in the present embodiment, a shift resistor 11 of FIG. 1 is used as at least one of the shift resistors 3a and 4a. Hereinafter, the start signal SPS (SPG) is referred to as SP, the number of steps L (m) of the shift resistor 11 is referred to as n, and the output signals are referred to as S₁ to S_n in order to respond to both of the shift resistors 3a and 4a.

[0067] To be specific, the shift resistor 11 includes a set/reset flip flop (SR flip flop) F1₍₁₎ and later, a flip flop section 12 operating at the driving voltage V_CC, and level shifter 13₍₁₎ and later which increase a voltage of a clock signal CK and applies the clock signal CK to the SR flip flop F1₍₁₎ and later. The clock signal CK smaller in an amplitude than the driving voltage V_CC is applied from the control circuit 5.

[0068] In the present embodiment, the level shifter 13₍₁₎ and later are disposed so as to respectively correspond to the SR flip flop F1₍₁₎ and later. As will be described later, the level shifter 13₍₁₎ and later are formed as current-driven level shifters, which are capable of increasing a voltage without causing any problems even when an amplitude of a clock signal CK is smaller than the driving voltage V_CC. Further, while a control signal ENA_i provides an instruction for operation, the i representing an integer between 1 and n, each level shifter 13_(i) can apply a clock signal CK_i, whose voltage has been increased, to the corresponding SR flip flop F1_(i) based on the clock signal CK and an inverse signal CK bar thereof. Furthermore, when a control signal ENA provides an instruction for suspension, the operation is suspended so as to prevent the clock signal CK_i from being applied to the corresponding SR flip flop F1_(i). While the operation is suspended, an input switching element (described later) is shut off so as to reduce power consumption of the level shifter 13_(i), that is caused by feedthrough current.

[0069] Meanwhile, the flip flop section 12 has a construction in which a start signal SP with a period width of one clock can be transmitted to the following step at each edge of a clock signal CK (rising edge and falling edge). To be specific, the output of the level shifter 13_(i) is applied as a set signal S bar having a negative logic via an inverter I1_(i) to the SR flip flop F1_(i). Moreover, an output Q of the SR flip flop F1_(i) is outputted as an output S_i of the shift register 11 and is outputted as a control signal ENA_i1 to the following level shifter 13_(i1). Additionally, to the level shifter 13₍₁₎ of the first step, a start signal SP from the control circuit 5 of FIG. 1 is applied as a control signal ENA₁ after a voltage of the start signal SP is increased. Furthermore, to the SR flip flop F1_(i), among set signals transmitted to the following SR flip flop F1, a signal, which is delayed by a pulse width of a transmitted pulse, is applied as a reset signal R. In the present embodiment, a pulse with one clock period width is transmitted. Hence, a signal delayed by one clock period, namely, a clock signal CK_(i2), which is applied to an SR flip flop F1_(i2) of two steps later, is applied as a reset signal having a positive logic.

[0070] Further, a clock signal CK is applied to a non-inverse input terminal and an inverse signal CK bar of the clock signal is applied to an inverse input terminal so that the SR flip flops F1₍₁₎, F1₍₃₎, and later of odd-numbered steps are set at a rising edge of the clock signal CK in the level shifter 13₍₁₎ and later of odd-numbered steps. In contrast, a clock signal CK is applied to an inverse input terminal and an inverse signal CK bar thereof is applied to a non-inverse input terminal in the level shifters 13₍₂₎, 13₍₄₎ and later of even-numbered steps so that the SR flip flops F1₍₂₎ and later of even-numbered steps are set at a falling edge of the clock signal CK.

[0071] According to this arrangement, as shown in FIG. 4, during a pulse input of a start signal SP, the level shifter 13₍₁₎ of the first step is operated, and a clock signal CK₁, whose voltage has been increased, is applied to the SR flip flop F1₍₁₎. Thus, the SR flip flop F1₍₁₎ is set when the clock signal CK firstly rises after the pulse input has started, and then, an output S₁ is shifted to a high level.

[0072] The output S₁ is applied to the level shifter 13₍₂₎ of the second step as a control signal ENA₂. Hence, the level shifter 13₍₂₎ outputs a clock signal CK₂ during a pulse output of the SR flip flop F1₍₁₎ (while control signal ENA₂S₁ is at a high level). Additionally, in the level shifter 13₍₂₎, a clock signal CK is applied to an inverse input terminal, so that the level shifter 13₍₂₎ outputs a signal whose polarity is opposite to that of the clock signal CK and voltage has been increased, as a clock signal CK₂. Thus, the SR flip flop F1₍₂₎ is set when the clock signal CK firstly falls after the output S₁ of the previous step has been shifted to a high level, an then, an output S₂ is shifted to a high level.

[0073] The output signal S_i is applied to the level shifter 13_(i1) of the following step as a control signal ENA_i1. Hence, the SR flip flop F1₍₂₎ and later in the second step and later output the output S₂ and later, each being delayed by a half period of the clock signal CK from the one of the previous step.

[0074] Meanwhile, to the level shifter 13_(i) of each step, an output CK_i2 of the level shifter 13_(i2) at two steps later is applied as a reset signal R. Therefore, the output S_i is at a high level for one clock period and is shifted to a low level. Hence, the flip flop section 12 can transmit a start signal SP of one clock period width to the following step at each edge (rising and falling) of a clock signal CK.

[0075] Here, the level shifter 13_(i) is respectively disposed for the SR flip flop F1_(i), so that even when the SR flip flop F1_(i) is disposed at many steps, it is possible to shorten a distance between the level shifter and the flip flop that correspond to each other, as compared with a case in which a voltage of a clock signal CK is increased by a single level shifter, and the clock signal CK is applied to all flip flops. Therefore, it is possible to shorten a transmitting distance of the clock signal CK_i after increasing the voltage and to reduce the load capacity of the level shifter 13_(i). Moreover, even when it is difficult to sufficiently secure the driving capacity of the level shifter 13_(i), for example, even when the level shifter 13_(i) is formed by a polycrystalline silicon thin film transistor, a buffer is not necessary because the load capacity is small. Consequently, it is possible to reduce the power consumption of the shift resistor 11.

[0076] Furthermore, when the flip flop F1_(i) does not require an input of the clock signal CK_i, for example, when the start signal SP and the low-level output S_i1 of the previous step are at a low level, the operation of the level shifter 13_(i) is suspended. In this state, the clock signal CK_i is not driven, so that power consumption required for driving cannot be generated. Furthermore, as will be described later, power supply to a level shift section 13a, which is disposed for each of the level shifter 13_(i), is suspended, an input switching element is shut off, and a feedthrough current cannot be applied. Therefore, although a large number (n) of current-driving level shifters are provided, power is consumed only by the level shifter 13_(i) under operation. Consequently, it is possible to dramatically reduce the power consumption of the shift resistor 11.

[0077] Additionally, the level shifter 13_(i) of the present embodiment judges a period when the clock signal CK_i is necessary for the SR flip flop F1_(i), namely, a period a) from a start of a pulse output of a start signal SP or an output S_i1 in the previous step b) to the setting of the SR flip flop F1_(i), only based on the start signal SP or the output S_i1 of the previous step. Consequently, it is possible to control the operation/suspension of the level shifter 13_(i) only by directly applying the start signal SP or an output S_i1 of the previous step, and to simplify the circuit construction of the shift resistor 11 as compared with when a circuit is provided for generating another control signal.

[0078] Further, in the present embodiment, while the level shifter 13_(i) is suspended, a clock input to the SR flip flop F1_(i) is shut off. Thus, it is possible to precisely transmit a start signal SP without the need for a switch brought into conduction in response to the necessity for a clock input, in addition to the level shifter 13_(i).

[0079] Here, as shown in FIG. 5, in each of the SR flip flops F1, a P-type MOS transistor P1, and N-type MOS transistors N2 and N3 are connected in series between the driving voltage V_CC and a ground level. A set signal S bar with a negative logic is applied to gates of the transistors P1 and N3. Further, a reset signal R with a positive logic is applied to the gate of the transistor N2. Furthermore, drain potentials of the transistors P1 and N2 connected to each other are respectively inverted in inverters INV1 and INV2 and are outputted as an output signal Q. Meanwhile, between the driving voltage V_CC and the ground level, P-type MOS transistors P4 and P5 and N-type MOS transistors N6 and N7 are respectively provided in series. The drains of the transistors P5 and P6 are connected to an input of the inverter INV1, and the gates of the transistors P5 and N6 are connected to an output of the inverter INV1. Moreover, a reset signal R is applied to the transistor P4, and a set signal S bar is applied to the gate of the transistor N7.

[0080] As shown in FIG. 6, in the SR flip flop F1, while a reset signal R is inactive (low level), when a set signal S bar is shifted to be active (low level), the transistor P1 is brought into conduction so as to shift the input of the inverter INV1 to a high level. Thus, the output signal Q of the SR flip flop F1 is shifted to a high level.

[0081] In this state, the reset signal R and the output of the inverter INV1 bring the transistors P4 and P5 into conduction. Further, the reset signal R and the output of the inverter INV1 shut off the transistors N2 and N6. Hence, even when the set signal S bar turns inactive, the input of the inverter INV1 is maintained at a high level and the output signal Q is also maintained at a high level.

[0082] Afterwards, when the reset signal R turns active, the transistor P4 is shut off and the transistor N2 is brought into conduction. Here, since the set signal S bar remains inactive, the transistor P1 is shut off and the transistor N3 is brought into conduction. Therefore, the input of the inverter INV1 is driven to a low level and the output signal Q is shifted to a low level.

[0083] Meanwhile, as shown in FIG. 7, the level shifter 13 of the present embodiment is provided with the level shift section 13a for level-shifting a clock signal CK; a power supply control section 13b for shutting off power supply to the level shift section 13a during a suspension period requiring no supply of a clock signal CK; input control sections (switch) 13c for shutting off the level shift section 13a and a signal line, where a clock signal CK is transmitted, during the suspension period; input switching element shutting-off control sections (input signal control section) 13d for shutting off the input switching element of the level shift section 13a during the suspension period; and an output stabilizing section (output stabilizing means) 13e for maintaining the output of the level shift section 13a at a predetermined value during the suspension period.

[0084] The level shift section 13a is provided with P-type MOS transistors P11 and P12, in which the sources are connected to each other, as a differential input pair of an unpitying step; a constant current source Ic for supplying a predetermined current to the sources of the transistors P11 and 12; N-type MOS transistors N13 and N14 which constitute a current mirror circuit and serve as active loads of the transistors P11 and P12; and transistors P15 and N16 having CMOS structures for amplifying an output of the differential input pair.

[0085] To the gate of the transistor P11, a clock signal CK is inputted via a transistor N31 (described later). To the gate of the transistor P12, an inverse signal CK bar of the clock signal is inputted via a transistor N33 (described later). Further, the gates of the transistors N13 and N14 are connected to each other and to the drains of the transistors P11 and N13. Meanwhile, the drains of the transistors P12 and N14, that are connected to each other, are connected to the gates of the transistors P15 and N16. Here, the sources of the transistors N13 and N14 are grounded via the N-type MOS transistor N21 serving as the power supply control section 13b.

[0086] Meanwhile, in the input control section 13c on the side of the transistor P11, the N-type MOS transistor N31 is disposed between the clock signal CK and the gate of the transistor P11. Moreover, in the input switching element shutting-off control section 13d on the side of the transistor P11, a P-type MOS transistor P32 is disposed between the gate of the transistor P11 and the driving voltage V_CC. In the same manner, to the gate of the transistor P12, an inverse signal CK bar of a clock signal is applied via the transistor N33 acting as the input control section 13c, and a driving voltage V_CC is applied via the transistor P34 acting as the input switching element shutting-off control section 13d.

[0087] Further, the output stabilizing section 13e has a construction in which an output voltage OUT of the level shifter 13 is stabilized to a ground level during the suspension period. A P-type MOS transistor P41 is provided between the driving voltage V_CC and the gates of the transistors P15 and N16.

[0088] Additionally, in the present embodiment, a control signal ENA is set so as to indicate the operation of the level shifter 13 at a high level. Hence, the control signal ENA is applied to the gates of the transistors N21 to P41.

[0089] In the level shifter 13 having the above construction, when the control signal ENA indicates operation (at a high level), the transistors N21, N31, and N33 are brought into conduction, and the transistors P32, P34, and P41 are shut off. In this state, current of the constant current source Ic passes through the transistors P11 and N13, or the transistors P12 and N14, and the transistor N21. Further, to the gates of the transistors P11 and P12, the clock signal CK or the inverse signal CK bar of the clock signal is applied. Consequently, to the transistors P11 and P12, current is applied in accordance with a voltage ratio of the gate and the source. Meanwhile, the transistors N13 and N14 act as active loads, so that voltage is applied to a connection of the transistors P12 and N14 in accordance with a voltage level difference between the CK and CK bar. The voltage, which serves as a gate voltage for the CMOS transistors P15 and N16, is amplified at the transistors P15 and N16 and is outputted as an output voltage OUT.

[0090] The level shifter 13 has a construction in which the clock signal CK switches conduction/shutting off of the transistors P11 and P12 at the unpitying step, namely, unlike a current-driven type, the transistors P11 and P12 of the unpitying step are continuously conducting during the operation. Current of the constant current source Ic is shunted in accordance with a voltage ratio of the gate and the source of each of the transistors P11 and P12, so that the clock signal CK is level-shifted.

[0091] Consequently, as shown in FIG. 4, the level shifter 13_(i) can output the output voltage OUT as the clock signal CK_i whose peak value is increased to a driving voltage Vcc (for example, about 15 V), the clock signal CK_i being identical to the clock signal CK with a peak value smaller than the driving voltage Vcc (for example, about 5 V).

[0092] In contrast, when the control signal ENA_i indicates suspension (low level), the transistor N21 shuts off current transmitted from the constant current source Ic via the transistors P11 and N13 or the transistors P12 and N14. In this state, current supply from the constant current source Ic is interrupted in the transistor N21, resulting in smaller power consumption. Further, in this state, current is not supplied to the transistors P11 and P12, so that the transistors P11 and P12 cannot act as a differential input pair; consequently, it is not possible to determine a potential of the output end, namely, a connecting point of the transistors P11 and N14.

[0093] Furthermore, in this state, the transistors N31 and N33 of the input control sections 13c are shut off. With this arrangement, a signal line for transmitting the clock signal CK(CK bar) is away from the gates of the transistors P11 and P12 of the unpitying step, and a gate capacity serving as a load capacity of the signal line is limited to the level shifter 13 in operation. As a result, although a plurality of level shifters 13_(i) are connected to the signal line, it is possible to reduce the load capacity on the signal line and to reduce power consumption of a circuit such as the control circuit 5 of FIG. 2 for driving the clock signal CK (CK bar).

[0094] Additionally, during the suspension, the transistors P32 and P34 of the input switching element shutting-off control sections 13d are conducting, so that each of the transistors P11 and P12 has a gate voltage being equivalent to the driving voltage Vcc; thus, the transistors P11 and P12 are shut off. Hence, as in the case of the transistor N21 being shut off, the power consumption can be reduced by a current outputted by the constant current source Ic. Here, in this state, the transistors P11 and P12 cannot act as a differential input pair, so that it is not possible to determine a potential of the output end.

[0095] In addition, when the control signal ENA indicates suspension, the transistor P41 of the output stabilizing section 13e is conducting. As a result, the output end, namely, a gate potential of the CMOS transistors P15 and N16 is equivalent to the driving voltage V_CC, and the output voltage OUT enters a low level. Thus, as shown in FIG. 4, when the control signal ENA_i indicates suspension, the output voltage OUT (CK_i) of the level shifter 13_(i) is maintained at a low level regardless of a state of the clock signal CK. Consequently, unlike the case of the output voltage OUT being irregular during the suspension of the level shifter 13_(i), it is possible to prevent malfunction of the SR flip flop F1_(i) and to achieve the shift resistor 11 being able to operate in a stable manner.

[0096] Embodiment 2

[0097] Unlike Embodiment 1, referring to FIGS. 8 to 14, the following explanation discusses a construction in which a shift resistor consists of D flip flops with a plurality of steps. Here, in the following Embodiments, those members that have the same functions and that are described in Embodiment 1 are indicated by the same reference numerals and the description thereof is omitted for convenience of explanation.

[0098] Namely, as shown in FIG. 8, a shift resistor 21 of the present embodiment is provided with a flip flop section 22 consisting of a D flip flop F2₍₁₎ and later with a plurality of steps, and a level shifter 23₍₁₎ and later which are disposed respectively for the D flip flop F2₍₁₎ and later and which have the same constructions as level shifter 13₍₁₎ and later of FIG. 1.

[0099] The D flip flop F2_(i) is a D flip flop in which an output Q is varied in response to an input D when a clock signal CK_i is at a high level, and the output Q is maintained at a low level. The output Q of the D flip flop F2_(i) is outputted as an output S_i and inputted to a D flip flop F2_(i1) of the following step. Here, a start signal SP is inputted to the D flip flop F2₍₁₎ of the first step.

[0100] Moreover, as shown in FIG. 1, the level shifter 23₍₁₎ and later of odd-numbered steps output a clock signal CK, whose voltage has been increased, as a clock signal CK₁ and later during the operation, and the level shifter 23₍₂₎ and later of even-numbered steps output a signal CK₂ and later, whose voltages have been increased with a polarity being opposite to the clock signal CK, in operation. Here, regardless of an odd or even step, the corresponding clock signal CK_i and an inverse signal of the clock signal CK_i, which is generated in an inverter I2_(i), are applied to the D flip flop F2_(i).

[0101] Here, the output S_i of the D flip flop F2_(i) does not vary until the clock signal CK_i rises. Therefore, unlike the SR flip flop F1_(i) of FIG. 1, the D flip flop F2_(i) requires the clock signal CK_i at a falling edge as well as a rising edge of the output S_i. Therefore, the present embodiment is provided with an OR circuit G1_(i) for computing an OR of the input and output of the level shifter 23_(i). The OR circuit G1_(i) outputs a computing result as the control signal ENA_i to the corresponding level shifter 23_(i).

[0102] As shown in FIG. 9, in the case of a pulse input of the start signal SP in the above construction, the control signal ENA₁ is shifted to a high level, and the clock signal CK1 whose voltage has been increased is inputted to the D flip flop F2₍₁₎. Consequently, after the pulse input of the start signal SP, the output S1 of the D flip flop F2₍₁₎ is shifted to a high level at a rising edge of the following clock signal CK₁. While the clock signal CK₁ is at a low level, even when the start signal is shifted to a low level, the output S₁ of the D flip flop F2₍₁₎ is maintained at a high level.

[0103] After the start signal SP is shifted to a low level, at the first rising edge of the clock signal CK₁, the output S₁ of the D flip flop F2₍₁₎ is shifted to a low level. Furthermore, in this state, the start signal SP and the output S₁ are at a low level, so that the OR circuit G1₍₁₎ shifts the control signal ENA₁ to a low level and suspends the level shifter 23₍₁₎.

[0104] Here, the output S_i of the D flip flop F2_(i) is inputted to the following D flip flop F2_(i1), and the clock signals CK_i and CK_i1 having opposite polarities to each other are inputted to the adjacent D flip flop F2_(i) and F2_(i1). Consequently, the flip flop section 22 can transmit the start signal SP to the following step at each edge (rising and falling) of the clock signal CK.

[0105] In the above construction, the level shifter 23_(i) is operated when the corresponding D flip flop F2_(i) requires an input of the clock signal CK_i, namely, a period from the start of a pulse input to the D flip flop F2_(i) to the end of a pulse output of the D flip flop F2_(i), and the level shifter 23_(i) can suspend its operation in other periods. As a result, in the same manner as Embodiment 1, it is possible to achieve the shift resistor 21 which can operate by the clock signal CK with an amplitude being smaller than the driving voltage V_CC and achieve small power consumption.

[0106] Further, unlike Embodiment 1, the flip flop section 22 of the present embodiment is constituted by the D flip flops which vary the output Q in response to the input D and the clock signal CK. Thus, even when a pulse width (number of clocks) of the start signal SP is changed, the start signal SP can be transmitted without causing any problems.

[0107] For example, in the case of the sampling section 3b of FIG. 2, when a sampling transistor for sampling an image data signal DAT has a small driving capability, a longer sampling period is required and the outputs S₁ to S_n need to have longer pulse widths (time). Meanwhile, even in the case of a pulse width having the same time period, the higher a frequency of the clock signal CK is, the number of the clocks increases. Therefore, regarding a pulse width of the start signal SP, an optimum value varies according to the driving capability of the sampling transistor and a frequency of the clock signal CK. Hence, as shown in the shift resistor 11 of FIG. 1, in the case of the construction in which a connecting point of a reset signal R is set in accordance with a pulse width (clock number) of the output S₁ and later, it is necessary to arrange a different circuit for each of the desired widths (clock numbers). Moreover, when the data signal line driving circuit 3 is driven by a clock signal CK with a different frequency, or when the same data signal line driving circuit 3 is used for driving a different display section 2, an optimum pulse width may not be secured, resulting in degradation in display quality.

[0108] In contrast, the shift resistor 21 of the present embodiment can output the outputs S₁ and later with desired pulse widths only by changing a pulse width of the start signal SP. Hence, it is possible to reduce the steps of designing the construction and to achieve an image display apparatus 1 which does not cause degradation in display quality even in the above-mentioned state.

[0109] However, as shown in FIG. 5, the SR flip flop F1 can be realized with fewer elements at higher operation speed as compared with a D flip flop F2 of FIG. 10 (described later), at the same moving speed. Moreover, in the output S_i1 of the previous step, it is possible to directly control the operation/suspension of the level shifter 13_(i) of the following step; hence, the OR circuit G1_(i) is not necessary. Consequently, when an optimum pulse width (clock number) can be previously determined and a high-speed shift resistor with a small circuit is demanded, the SR flip flop F1 is more preferable.

[0110] Here, for example, as shown in FIG. 10, each of the D flip flops F2 has a construction in which P-type MOS transistors P51 and P52 and N-type MOS transistors N53 and N54 are connected in series between a driving voltage V_CC and the ground level. An input signal D is applied to the gates of the transistors P52 and N53, and the drain potentials of the transistors P52 and N53 are inverted at an inverter INV51 and is outputted as an output Q. Further, between a driving voltage V_CC and the ground level, P-type MOS transistors P55 and P56 and N-type MOS transistors N57 and N58 are connected in series. The drains of the transistors P56 and N57 are inputted to an input of the inverter INV51 and the gates thereof are connected to an output of the inverter INV51. Moreover, an inverse signal CK bar of a clock signal is applied to the gates of the transistors P51 and N58, and a clock signal CK is applied to the gates of the transistors N54 and P55.

[0111] In the D flip flop F2 having the above construction, while the clock signal CK is at a high level, the transistors P51 and N54 are conducting and the transistors P55 and N58 are shut off. With this arrangement, the input D is inverted at the transistors P52 and N53 and is inverted at the inverter INV 51. As a result, the output Q is shifted to the same value as the input D. In contrast, while the clock signal CK is at a low level, the transistors P51 and N54 are shut off, so that the transistors P52 and N53 cannot invert the input D. Further, in this state, the transistors P55 and N58 are conducting, so that the output of the inverter INV51 returns to the input thereof. As a result, while the clock signal CK is at a low level, the output Q is maintained at a value of a falling edge of the clock signal CK even when the input D is at a high level. Therefore, as shown in FIG. 11, after the input D is changed, the output Q of the D flip flop F2 is varied in response to the input D at the first rising edge of the clock signal CK.

[0112] Meanwhile, as shown in FIG. 12, each of the OR circuits G1 is provided with a series circuit consisting of P-type MOS transistors P61₍₁₎ and later corresponding to the inputs IN₍₁₎ and later, a parallel circuit consisting of N-type MOS transistors N62₍₁₎ and later corresponding to the inputs IN₍₁₎, and a CMOS inverter consisting of a P-type MOS transistor P63 and an N-type MOS transistor N64. Here, the OR circuit G1 is an OR circuit with two inputs, so that the two transistors P61 and the two transistors N62 are respectively provided. Inputs IN₍₁₎ are applied to the gates of the transistors P61₍₁₎ and N62₍₁₎, and inputs IN₍₂₎ are applied to the gates of the transistors P62₍₂₎ and N62₍₂₎. Further, the series circuit and the parallel circuit are connected in series and are disposed between the driving voltage V_CC and the ground level. Moreover, a connecting point of the series circuit and the parallel circuit is connected to the input end of the CMOS inverter, namely, to the gates of the transistors P63 and N64. With this arrangement, the OR circuit G1 can output an OR of the inputs IN₍₁₎ and IN₍₂₎ from the drains of the transistors P63 and N64, that serve as the output terminal of the CMOS inverter.

[0113] Incidentally, in FIG. 8, the OR circuit G1_(i) is provided for finding an OR of the input and the output of the D flip flop F2_(i) and for providing an instruction of operation/suspension to the level shifter 23_(i). However, if the level shifters themselves can find an OR of the input and the output of the D flip flop F2_(i) and judge operation/suspension, the OR circuit G1_(i) can be omitted.

[0114] To be specific, as shown in FIG. 13, in a shift resistor 21a of the present variation, a level shifter 24_(i), which operates when the control signal ENA₁ or ENA₂ is active (true), is provided instead of the level shifter 23_(i). Accordingly, the OR circuit G1_(i) of FIG. 8 is omitted, and the input and the output of the D flip flop F2_(i) are directly inputted as the control signals ENA₁ or ENA₂ to the corresponding level shifter 24_(i).

[0115] As shown in FIG. 14, the level shifter 24 has virtually the same construction as the level shifter 13 of FIG. 7; however, unlike the level shifter 13, power supply control sections 24b to an output stabilizing section 24e are provided with transistors N21 to P41, each being provided in the same number as each of the control signals ENA₁ and ENA₂ (in this case, respectively two) so as to correspond to the control signals ENA₁ and ENA₂. To be specific, in the power supply control section 24b, the transistors N21₍₁₎ and N21₍₂₎ are connected in parallel. In the same manner, in the input control section 24c corresponding to the transistor P11, the transistors N31₍₁₎ and N31₍₂₎ are connected in parallel, and in the input control section 24c corresponding to the transistor P12, the transistors N33₍₁₎ and N33₍₂₎ are connected in parallel. Meanwhile, in the output stabilizing section 24e, the transistors P41₍₁₎ and P41₍₂₎ are connected in series. Each of the input switching element shutting-off control sections 24d consists of the transistors P32₍₁₎ and P32₍₂₎ connected in series, or the transistors P34₍₁₎ and P34₍₂₎ connected in series. Further, in the present embodiment, the shift register 21a transmits a high-level pulse signal, so that the control signal ENA₁ is applied to the gate of the transistor corresponding to ENA₁ (subscript is ₍₁₎) among the transistors N21₍₁₎ to P41₍₂₎, and the control signal ENA₂ is applied to the gate of the transistor corresponding to the control signal ENA₂ (subscript is ₍₂₎).

[0116] According to the above construction, when at least one of the control signal ENA₁ and ENA₂ is at a high level, the transistor N21₍₁₎ or N21₍₂₎, the transistor N31₍₁₎ or N31₍₂₎, and the transistor N33₍₁₎ or N33₍₂₎ are brought into conduction. Further, the transistor P32₍₁₎ or P32₍₂₎ the transistor P34₍₁₎ or P34₍₂₎, and the transistor P41₍₁₎ or P41₍₂₎ are shut off. Consequently, in the same manner as the level shifter 13, the level shifter 24 is operated. In contrast, when both of the control signals ENA₁ and ENA₂ are at a low level, the N-type transistors N21₍₁₎ to N34₍₂₎ are all shut off and the P-type transistors P31₍₁₎ to P41₍₂₎ are all brought into conduction, so that the level shifter 24 is suspended in the same manner as the level shifter 13. Consequently, in the same manner as the level shifter 23_(i) of FIG. 8, the level shifter 24_(i) can be operated/suspended according to the input and the output of the corresponding D flip flop F2_(i), thereby achieving the same effect.

[0117] Embodiment 3

[0118] Incidentally, in Embodiments 1 and 2, a level shifter is provided for each flip flop. However, when a smaller circuit is considerably required, it is possible to provide a level shifter for a plurality of the flip flops, as will be described in the following Embodiments. Referring to FIGS. 15 to 19, the present embodiment describes a construction in which a level shifter is provided for a plurality of SR flip flops.

[0119] To be specific, in a shift resistor 11a of the present embodiment, as shown in FIG. 15, N pieces of SR flip flops F1 are divided for every K pieces into a plurality of blocks B_i to B_P. Moreover, a level shifter 13 is disposed for each of the blocks B. Hereinafter, for convenience of explanation, a j_th SR flip flop F1 in an i_th block B_i is referred to as F1_(i,j), where i represents an integer between 1 and P and j represents an integer between 1 and K.

[0120] Furthermore, in the present embodiment, in each block B_i, an OR circuit G2_(i) is provided for instructing a control signal ENA₁ to the level shifter 13_(i). The OR circuit G2_(i) is an OR circuit with K inputs that calculates an OR of an input signal to the block B_i and each output signal of the SR flip flops F1 _(i,1) to F1_i,(K1) except for at the final step of the block B_i, and outputs the OR to the level shifter 13_(i). Here, a start signal SP serves as an input signal to the block B_i in the block B₁ of the first step, and an output signal of the previous block B_i1 serves as an input signal in the block B_i of the second step or later. For example, as shown in FIG. 16, the above OR circuit G2 can be realized by increasing the transistors P61 and the transistors N62 to the number of inputs (in this case, K inputs) in the OR circuit G1 of FIG. 12.

[0121] With this arrangement, as shown in FIG. 17, from the start of a pulse input to the block B_i to the end of a pulse output regarding the output S_i,(K1) of the SR flip flop F1_(i,(K1)), which belongs to a step before the last one, a control signal ENA_i to the level shifter 13_(i) is at a high level. As a result, the level shifter 13_(i) can output a clock signal CK_i at least when an input of the clock signal CK_i is required in any one of the SR flip flops F1_(i,1) to F1_(i,K), namely, from the start of the pulse input to the setting of the SR flip flop F1_(i,K) of the final step. Further, after the SR flip flop F1_(iK) is set, the level shifter 13_(i) can suspend its operation at the end of the pulse output of the output S_i,(k1) of the SR flip flop F1_(i,(K1)).

[0122] In the present embodiment, the level shifter 13_(i) continues to output the clock signal CK_i when a clock input is necessary in any one of the SR flip flops F1_(i,j) in the block B_i. Therefore, if the clock signal CK_i is applied to the SR flip flops F1_(i,j) as it is, the SR flip flop F1_(i,j) is set after being reset; consequently, a plurality of pulses are generated from a single pulse of the start signal SP. Hence, as shown in FIG. 15, the shift register 11a is provided with a switch SW_i,j between the level shifter 13_(i) and the SR flip flops F1_(i,j) so as to apply the clock signal CK_i to the SR flip flops F1_(i,j) only when the SR flip flops F1_(i,(j1)) of the previous step outputs a pulse. Moreover, while the switch SW_i,j is shut off, in order to interrupt a set input to the SR flip flop F1_(i,j), a driving voltage V_CC is applied to a negative-logic set terminal S bar of the SR flip flop F1_(i,j) via a P-type MOS transistor P_i,j. In the shift register 11a of the first step, a start signal SP is applied to the gate of a transistor P_1,1, and in other steps, an output S_i,j1 of the SR flip flop F1_(i,j1) of the previous step is applied to the gate of the transistor P_i,j. Hence, while the switch SW_i,j is shut off, the transistor P_i,j is brought into conduction and the set terminal S bar is maintained at a predetermined potential (in this case, the driving voltage V_CC) so as to interrupt the set input. Consequently, the start signal SP is transmitted without any problems. Additionally, to an SR flip flop F1 which does not receive the clock signal CK_i after a reset, for example, to the SR flip flop F1_(i,K) of the final step, the clock signal can be directly inputted without passing through the switch SW.

[0123] According to this arrangement, as described in Embodiment 1, a distance between the level shifter 13 and the SR flip flop F1 is longer as compared with the construction in which the level shifter 13 is provided for each of the SR flip flops F1. However, as compared with the conventional art in which a single level shifter applies a clock signal CK to all SR flip flops F1, this arrangement makes it possible to reduce a distance between the level shifter 13 and the SR flip flop F1 and to reduce the buffer. Thus, virtually in the same manner as Embodiment 1, it is possible to realize the shift register 11a achieving small power consumption.

[0124] In this case, when the number of the SR flip flops F1 in the block B is increased, it is possible to reduce the number of the level shifters 13 in the shift register 11a, thereby simplifying the circuit construction. Meanwhile, in the case of the excessive SR flip flops, the driving capability of the level shifter 13 becomes insufficient, so that a buffer is necessary, resulting in larger power consumption. Therefore, when the size of the circuit needs to be reduced without a large increase in power consumption, it is more preferable to set the number of the SR flip flops F1 in each of the blocks B such that the level shifter 13_(i) can apply the clock signal CK_(i) without a buffer.

[0125] Here, in the above Embodiment, the construction is taken as an example, in which the OR circuit G2 controls the operation/suspension of the level shifter 13. However, as shown in FIG. 18, in the same manner as the level shifter 24 of FIG. 13, it is also possible to allow the level shifter 14 to determine the operation/suspension based on the input signals transmitted to the OR circuit G2. As shown in FIG. 19, the level shifter 14 can be realized by, for example, providing each of the transistors N21 to P41 of the level shifter 24 shown in FIG. 14 in the same number as the inputs (in this case, the number is K).

[0126] Embodiment 4

[0127] Referring to FIGS. 20 to 24, the following explanation describes a construction in which a level shifter is provided for a plurality of D flip flops. Namely, as shown in FIG. 20, a shift register 21b of the present embodiment is similar to a shift register 21 of FIG. 8; however, N pieces of D flip flops F2 are divided for every K pieces into a plurality of blocks B₁ to B_P. Further, a level shifter 23 is provided for each of the blocks B.

[0128] Moreover, in the present embodiment, each of the blocks B_i is provided with an OR circuit G3_(i) for instructing a control signal ENA_i to the level shifter 23_(i). The OR circuit G3_i is an OR circuit having (K1) inputs. The OR circuit G3_i calculates ORs of the inputs and outputs of the D flip flops F2_(i,1) to F2_(i,K) and outputs the ORs to the level shifter 23_(i). Here, an input signal to the D flip flop F2_(i,1) of the final step is a start signal SP in the block B1 of the final step. In the second step or later, an input signal is an output signal from the block B_i1 of the previous step. The OR circuit G3 can be realized by, as shown in FIG. 21, increasing the transistors P61 and the transistors N62 of an OR circuit G1 shown in FIG. 12 to the number of the inputs (in this case, the number is K1).

[0129] With this arrangement, as shown in FIG. 22, when any one of the D flip flops F2_(i,1) to F2_(i,K) requires an input of a clock signal CK_i in the block B_i, namely, from the start of a pulse input to the block B_i to the end of the pulse output of the D flip flop F2_(i,K) in the final step, the control signal ENA_i to the level shifter 23_(i) is at a high level, so that the level shifter 23_(i) can transmit the clock signal CK_i. Further, the control signal ENA_i is at a low level in the other periods, so that the level shifter 23_(i) can suspend its operation.

[0130] According to this arrangement, a distance between the level shifter 23 and the D flip flop F2 is longer as compared with a shift register 21 of Embodiment 2, in which a level shifter 23 is provided for each D flip flop F2. However, as compared with the conventional art in which a single level shifter supplies a clock signal CK to all D flip flops, this arrangement makes it possible to reduce a distance between the level shifter 23 and the D flip flop F2 and to reduce the buffer. Therefore, virtually in the same manner as Embodiment 2, it is possible to realize the shift register 21b achieving small power consumption.

[0131] Furthermore, in the same manner as Embodiment 3, the present embodiment makes it possible to reduce the number of the level shifters 23 to less than the level shifters 21. Additionally, when it is necessary to reduce the size of the circuit without a large increase in power consumption, it is more preferable to set the number of the D flip flops F2 in each of the blocks B_i such that the level shifter 23_(i) can apply the clock signal CK_(i) without a buffer.

[0132] Here, in FIG. 20, the construction is taken as an example, in which the OR circuit G3 controls the operation/suspension of the level shifter 23. However, in the same manner as the shift register 21c of FIG. 23, as shown in the shift register 21c of FIG. 23, it is also possible to allow the level shifter 25 to determine the operation/suspension based on the input signals transmitted to the OR circuit G3. As shown in FIG. 24, the level shifter 25 can be realized by, for example, providing each of the transistors N21 to P41 in the level shifter 14 of FIG. 19, in the same number as the inputs (in this case, the number is K).

[0133] Embodiment 5

[0134] Embodiment 3 (and Embodiment 4) describes the construction in which a level shifter or an OR circuit is used to obtain an OR of K, (K1) signals so as to control the operation/suspension of the level shifter. Meanwhile, referring to FIGS. 25 to 29, the present embodiment describes a construction in which a latch circuit is used for controlling the operation/suspension of the level shifter.

[0135] To be specific, as shown in FIG. 25, a shift register 11c of the present embodiment is provided with a latch circuit 31_(i) instead of an OR circuit G2_(i) of a shift register 11a shown in FIG. 15. The latch circuit 31 is arranged so as to change an output by using as triggers a) a pulse input to an SR flip flop F1 _(i,1) of the first step in a block B_i and b) a pulse output from an SR flip flop F1_(i,K) of the final step in a block B_i. With this arrangement, between the start of the pulse input and the start of the pulse output, it is possible to instruct an operation to a level shifter 13_(i).

[0136] For example, in the first block B₁, a start signal SP inverted in an inverter 31a is applied to the latch circuit 31 as a set signal S bar having a negative logic, as shown in FIG. 26. Further, the latch circuit 31 is provided with an SR flip flop 31b, where an output S_1,K of the SR flip flop F1_(1,K) in the final step is applied as a reset signal R having a positive logic. Additionally, in the following block B_i and later, an output of the block B_i1, in the previous step is applied instead of the start signal SP.

[0137] In the above arrangement, as shown in FIG. 27, the latch circuit 31_(i) sets a control signal ENA_i at a high level a) from when an input to the SR flip flop F1_(i,1) of the final step is shifted to a high level b) to when the output S_i,K is shifted to a high level. Thus, the level shifter 13_(i) can continue to apply a clock signal CK_i during this period. Moreover, when the output S_i,K is shifted to a high level, the control signal ENA_i is shifted to a low level, so that the level shifter 13_(i) suspends its operation. Consequently, in the same manner as Embodiment 3, it is possible to realize the shift register 11c achieving smaller power consumption as compared with the conventional art.

[0138] Furthermore, unlike an OR circuit G2_(i) (level shifter 14_(i)) of Embodiment 3, in which the operation/suspension of a level shifter 13_(i) (14_(i)) is judged based on K signals, two signals trigger the latch circuit 31 to generate a control signal ENA_i, regardless of the number of steps K of the SR flip flops F1 in a block B_i. Therefore, it is possible to reduce the number of signal lines to two. The signal lines transmit a signal required for judging. The more signal lines for judging, the more intersections of the signal lines for judging and the signal lines for transmitting the output S_i,j and the clock signals CK and CK_i, resulting in a capacity of each of the signal lines. Meanwhile, in the present embodiment, the signal lines for judging is reduced to two, so that it is more possible to prevent an increase in a wire capacity, the increase being caused by the signal lines for judging; thus, it is possible to realize the shift register 11c achieving small power consumption.

[0139] In FIG. 26, the construction in which the latch circuit 31_(i) is constituted by the SR flip flops is taken as an example. However, the construction is not particularly limited. For example, even when a latch circuit 32 of FIG. 28 is used instead of the latch circuit 31_(i), the same effect can be achieved as long as two signals serve as triggers to control the operation/suspension of the level shifter 13_(i).

[0140] The latch circuit 32 is provided with two D flip flops 32a and 32b constituting two frequency dividers, an NOR circuit 32c for calculating a NOT of an OR of the start signal SP and the output S_1,K, and an inverter 32d for inverting an output of the NOR circuit 32c. An output Q of the D flip flop 32a is inputted to the D flip flop 32a via the D flip flop 32b. Further, an output L_SET of the inverter 32d is applied to the D flip flop 32a as a clock. Meanwhile, an output of the NOR circuit 32c is applied to the D flip flop 32b as a clock. Furthermore, an output L_OUT of the D flip flop 32a is outputted as a control signal ENA₁. Consequently, as shown in FIG. 29, the latch circuit 32_(i) can output a high-level control signal ENA₁ a) from the start of a pulse input to the SR flip flop F1_(i,1) in the first step b) to a rising edge of the output S_i,K, so that an instruction is provided to operate the level shifter 13_(i).

[0141] Additionally, in the present embodiment, a) the start of a pulse input to the SR flip flop F1_(i,1) in the first step and b) the start of the pulse output of the SR flip flop F1_(i,K) in the final step are used as triggers of the latch circuit (3132); however, the triggers are not particularly limited. As the triggers, it is also possible to adopt a signal for setting the control signal ENA_i at an active level before a period when the SR flip flop F1 of the block B_i requires a clock signal CK_i, and a signal for setting the control signal ENA_i at an inactive level after the period, in order to achieve the same effect.

[0142] Embodiment 6

[0143] Referring to FIGS. 30 to 34, the present embodiment describes a construction in which a latch circuit controls the operation/suspension of a level shifter in a shift register using D flip flops.

[0144] To be specific, a shift register 21d of the present embodiment is provided with a latch circuit 33_(i), which uses as triggers, a) a pulse input to the D flip flop F2_(i,1) in the first step and b) a pulse output of the D flip flop F2_(i,K) in the final step, virtually in the same manner as a latch circuit 31_(i) of FIG. 25, instead of an OR circuit G3_(i) of a shift register 21b shown in FIG. 20. However, as described above, in the case of the D flip flop, a clock signal CK_i is necessary until the D flip flop F2_(i,K) of the final step stops a pulse output. Therefore, the latch circuit 33_(i) is arranged so as to instruct an operation to the level shifter 23_(i) from the start of the pulse input to the end of the pulse output.

[0145] To be specific, as shown in FIG. 31, in the first block B₁, the latch circuit 33 is provided with a NOR circuit 33c for calculating a NOT of an OR of an output signal L_OUT and an output S_1,K of the final step, and an inverter 33d for inverting the calculation result, in addition to the latch circuit 31 of FIG. 26. Here, in the following block B_i, an output of the block B_i1, of the previous step is applied instead of the start signal SP.

[0146] As shown in FIG. 32, in the above arrangement, the latch circuit 33₍₁₎ sets the control signal ENA₁ at a high level a) from when an input to the D flip flop F2_(1,1) of the first step is shifted to a high level b) to when the output S_1,K is shifted to a low level. Thus, the level shifter 23₍₁₎ can continue to apply the clock signal CK₁ during this period. Further, when the output S_1,K is shifted to a low level, the control signal ENA₁ is shifted to a low level, so that the level shifter 23₍₁₎ suspends its operation. Consequently, in the same manner as Embodiment 4, it is possible to achieve the shift register 21d smaller in power consumption than the conventional art.

[0147] Moreover, like Embodiment 5, the present embodiment makes it possible to reduce the number of signal lines required for judging the operation/suspension of the level shifter 23. Hence, it is more possible to prevent an increase in a wiring capacity, the increase being caused by the signal lines for judging, as compared with Embodiment 4. Furthermore, it is possible to realize the shift register 21d achieving small power consumption.

[0148] Here, in FIG. 31, the construction in which the latch circuit 33 is constituted by the SR flip flops is taken as an example. However, the construction is not particularly limited. For example, even when a latch circuit 34 of FIG. 33 is used instead of the latch circuit 31_(i), the same effect can be achieved as long as two signals serve as triggers to control the operation/suspension of the level shifter 13.

[0149] The latch circuit 34 is provided with the NOR circuit 33c and the inverter 33d of FIG. 31 in addition to a latch circuit 32 of FIG. 28. Consequently, as shown in FIG. 34, the latch circuit 34 can output a high-level control signal ENA₁ a) from the start of a pulse input to the D flip flop F2_(i,1) in the first step of the block B_i b) to the end of a pulse output of the D flip flop F2_(i,K) in the final step, so as to instruct an operation to the level shifter 23_(i).

[0150] Here, in the present embodiment, a) the start of a pulse input to the D flip flop F2_(i,1) of the first step and b) the end of a pulse output of the D flip flop F2_(i,K) of the final step are adopted as the triggers of the latch circuits (33 to 34). However, the triggers are not particularly limited. As the triggers, it is also possible to adopt a signal for setting the control signal ENA_i at an active level before a period when the SR flip flop F1 in the block B_i requires a clock signal CK_i, and a signal for setting the control signal ENA_i at an inactive level after the period, in order to achieve the same effect.

[0151] Embodiment 7

[0152] Referring to FIG. 35, the following explanation describes a construction being able to further reduce power consumption, regarding shift registers 21b to 21d, in which a level shifter 23 (24, 25) applies a clock signal CK to a plurality of D flip flops F2 in the same manner as Embodiments 4 and 6.

[0153] To be specific, the shift registers of the present embodiment have the same constructions as the shift registers 21b to 21d except that a clock signal control circuit 26_(i,j) is provided for each of the D flip flops F2 _(i,j). Further, the level shifter 23_(i)(24_(i), 25_(i): hereinafter, represented by 23_(i)) applies a clock signal CK_(i), in which a voltage has been increased, only to the D flip flops F2 requiring a clock input.

[0154] As shown in FIG. 35, the clock signal control circuit 26_(i,j) is provided with a switch SW1_(i,j) disposed on a signal line for transmitting the clock signal CK_i, and a switch SW2_(i,j) disposed on a line for transmitting an inverted signal CK_i bar of the clock signal CK_i. In the same manner as the level shifter 23_(i,j) of FIG. 8, the switches SW1_(i,j) and SW2_(i,j) are controlled by an OR circuit G1_(i,j) for calculating an OR of the input and the output of the D flip flop F2_(i,j), the switches are brought into conduction when the D flip flop F2_(i,j) requires the clock signal CK_i(CK_i bar), and the switches are shut off when the clock input is not necessary. Moreover, the clock signal control circuit 26_(i,j) is provided with a) an N-type MOS transistor N71_(i,j) disposed between a clock input terminal of the D flip flop F2_(i,j) and a ground potential and b) a P-type MOS transistor P72_(i,j) disposed between an inverted clock input terminal of the D flip flop F2_(i,j) and a driving voltage V_CC. An output of the OR circuit G1_(i,j) is inverted in an inverter INV71_(i,j), and then, the output is applied to a gate of the transistor N71_(i,j). Meanwhile, the output of the OR circuit G1_(i,j) is applied to the gate of the transistor P72_(i,j).

[0155] According to this arrangement, when the corresponding D flip flop F2_(i,j) requires the clock signal CK_i (CK_i bar), whose voltage has been increased, the switch SW1_(i,j) (SW2_(i,j)) is brought into conduction so as to apply the clock signal CK_i (CK_i bar) to the D flip flop F2_(i,j). Meanwhile, when the clock input is not necessary, the switches SW1_(i,j) and SW2_(i,j) are shut off. Namely, for example, circuits such as the D flip flop F2_(i,j) following the switches SW1_(i,j) and SW2_(i,j) are separated from the level shifter 23_(i). Moreover, when the clock input is not necessary, the transistor N71_(i,j) and P72_(i,j) are brought into conduction so as to maintain the clock input terminal and the inverted input terminal of the D flip flop F2_(i,j) at predetermined values (low level and high level). With this arrangement, it is possible to prevent malfunction of the D flip flop F2_(i,j), unlike a construction in which the input terminals are irregular.

[0156] According to this arrangement, when the clock signal is not necessary, the circuits following the switches SW1_(i,j) and SW2_(i,j) are separated from the level shifter 23_(i). Therefore, the level shifter 23_(i) needs to drive only the D flip flop F2_(i,j) requiring the clock signal CK_(i) at this point. Hence, as compared with a construction in which all the D flip flops F2_(i,1) to F2_(i,K) are driven in the block B_i, a loading of the level shifter 23_(i) can be considerably reduced, resulting in smaller power consumption. Consequently, it is possible to realize a shift register achieving small power consumption.

[0157] In the above description, the construction is taken as an example, in which the clock signal control circuit 26_(i,j) is provided for each D flip flop F2_(i,j). However, the construction is not particularly limited. For instance, it is possible to provide the clock signal control circuit 26 for a plurality of the D flip flops F2. In this case, while the D flip flop F2 connected to the switches SW1 and SW2 requires a clock input, namely, a) from the start of a pulse input to the D flip flop F2 of the first step b) to the end of a pulse output of the D flip flop F2 of the final step, the switches SW1 and SW2 are controlled by a circuit such as the OR circuit G3 of FIG. 20 and the latch circuit 33 (34) of FIG. 30 (33); thus, the switches SW1 and SW2 are brought into conduction. In this case, as compared with the construction in which the clock signal control circuit 26 is provided for each of the D flip flops F2, the load capacity of the level shifter 23 (24, 25) is larger. However, the number of the clock signal control circuits 26 is reduced so as to simplify the circuit construction.

[0158] Embodiment 8

[0159] Incidentally, for example, regarding the above Embodiments, in a data signal line driving circuit 3 and a scanning signal line driving circuit 4 of FIG. 2, an output of the shift register (11, 11a to 11c, 21, 21a to 21d) in each step may be directly used as a signal for indicating a timing, or a signal, which is obtained by performing a logical operation on outputs of a plurality of the steps, may be used as a timing signal.

[0160] Referring to FIGS. 36 and 37, the following explanation describes a construction for suitably performing a logical computing outputs of a plurality of steps in a shift register using SR flip flops F1 like Embodiments 1, 3, and 5. Here, the construction can be used in other embodiments as long as the SR flip flop F1 is adopted therein. In the following, Embodiment 1 is taken as an example.

[0161] To be specific, with the construction of a shift register 11 of FIG. 1, a shift register lid of the present embodiment is provided with an AND circuit G4_(i) which computes an AND of two outputs S_i and S_i1 being adjacent to each other, and outputs the result as a timing signal SMP_i. Further, before an SR flip flop F1₍₁₎ of the first step, an SR flip flop F1₍₀₎ is provided, and an AND circuit G4₍₀₎ is provided for computing an AND of an output S₀ of the SR flip flop F1₍₀₎ and an output S₁ and for outputting the result. Moreover, an inverse signal SP bar of a start signal SP is applied to the SR flip flop F1₍₀₎ as a set signal having a negative logic. The output of the SR flip flop F1₍₀₎ is inputted to a level shifter 13₍₁₎ of the following step as a control signal ENA₁. Additionally, an output CK₂ of a level shifter 13₍₂₎ is applied to the SR flip flop F1₍₀₎ in the same manner as the SR flip flop F1_(i) of other steps. The level shifter 13₍₂₎ corresponds to the number of steps (two steps in this case) according to a pulse width of a transmitted pulse signal.

[0162] In this construction, among outputs S₀, S₁, and later of the SR flip flops F1₍₀₎, F1₍₁₎, and later, only the output S₀ is connected to a single AND circuit G4₍₀₎. Meanwhile, each of the other outputs S_i is connected to two circuits of AND circuits G4_(i1) and G4₍₀₎. As a result, the SR flip flop F1₍₀₎ and the other SR flip flops F1_(i) have different outputting loads. For this reason, even if the SR flip flop F1₍₀₎ and the other SR flip flops F1_(i) are driven at the same timing, the output S₀ and the other outputs S₁ and later are different from one another in a delay time to a clock signal CK. Therefore, in the case of a high frequency of the clock signal, it is necessary to reduce irregular timings resulted from a shift of a delay time. Hence, a dummy signal DUMMY, which is not used in the following circuits, is used as an output signal of the AND circuit G4₍₀₎, and only outputs SMP₁ and later of the AND circuits G4₍₁₎ and later are used for extracting an image signal.

[0163] In the above construction, unlike the other steps, the inverse signal SP bar, which is not in synchronization with the clock signal CK, is applied to the SR flip flop F1₍₀₎ as a set signal having a negative logic. Thus, a timing (a rising edge, a pulse width, etc.) of the output S₀ is different from those of the outputs S₁ and later of the SR flip flop F1₍₁₎ and later. However, as mentioned above, the output S₀ is not used in the following circuits as the dummy signal DUMMY. Therefore, even if the timing of the output so is different, the shift register 11d can output the timing signal SMP₁ and later whose timings differ between predetermined time periods, without any problems.

[0164] Furthermore, in the above construction, the inverse signal SP bar is applied to the SR flip flop F1₍₀₎, and the level shifters 13 are omitted. Consequently, as compared with a construction in which the SR flip flop F1₍₀₎ is provided with the level shifters 13, the number of the level shifters 13 can be reduced.

[0165] Additionally, in Embodiments 1 to 8, the current-driven level shifters (13, 14, and 23 to 25) are taken as examples. However, as shown in FIG. 38, a voltage-driven level shifter 41 is also available. As an input switching element, a level shift section 41a of the level shifter 41 is provided with an N-type MOS transistor N81 which is conducted/shut off in response to a clock signal CK, and an N-type MOS transistor N82 which is conducted/shut off in response to an inverse signal CK bar of the clock signal CK. To a drain of each of the transistors N81 (N82), a driving voltage V_CC is applied via P-type MOS transistors P83 (P84) acting as loads. Meanwhile, the sources of the transistors N81 and N82 are grounded. Moreover, a potential at a connecting point between the transistors N82 and P84 is outputted as an output OUT of the level shifter 41. Further, the potential at the connecting point between the transistors N82 and P84 is also applied to a gate of the transistor P83. In the same manner, a potential at a connecting point between the transistors N81 and P83 is outputted as an inverse output OUT bar of the level shifter 41 and is applied to the gate of the transistor P84.

[0166] On the other hand, the level shifter 41 is provided with N-type MOS transistors N91 and N92 serving as input release switch sections (switch) 41b. When the level shifter 41 is operated, the clock signal CK is applied to the gate of the transistor N81 via the transistor N91. Furthermore, the inverse signal CK bar of the clock signal CK is applied to the gate of the transistor N82 via the transistor N92.

[0167] Additionally, the level shifter 41 is provided with an N-type MOS transistor N93 and a P-type MOS transistor P94 serving as input stabilizing sections 41c. With this arrangement, when the level shifter 41 is suspended, the gate of the transistor N81 is grounded via the transistor N93. Meanwhile, the driving voltage V_CC is applied to the gate of the transistor N82 via the transistor P94. Moreover, the input stabilizing sections 41c correspond to outputting stabilizing means described in claims so as to control voltage inputted to the transistors N81 and N82 and to stabilize an output. Here, the level shifter 41 is driven by voltage so as to consume electricity only when the output OUT is changed. Hence, even when an output voltage is controlled by an input voltage during the suspension of the level shifter 41, electricity is not consumed.

[0168] In the present embodiment, when a control signal ENA is at a high level, an instruction is provided for operating the level shifter 41. Therefore, the control signal ENA is applied to the gates of the transistors N91, N92, and P94. On the other hand, the control signal ENA is inverted in an inverter INV91 and is applied to the transistor N93.

[0169] In the above construction, when the control signal ENA is at a high level, the transistors N91 and N92 are brought into conduction. Further, the transistors N81 and N82 are conducted/shut off in response to the clock signal CK and the inverse signal CK bar. With this arrangement, the output OUT rises to the driving voltage V_CC when the clock signal CK is at a high level. Meanwhile, when the clock signal CK is at a low level, the output OUT is at a ground level.

[0170] In contrast, when the control signal ENA is at a low level, the transistors N93 and P94 are brought into conduction. Thus, the transistor N81 is shut off and the transistor N82 is brought into conduction. Consequently, the output OUT is maintained at a ground level, and the inverse output OUT bar is maintained at the driving voltage V_CC. Furthermore, in this state, the transistors N91 and N92 are shut off. Therefore, the gate of the transistor N81 (N82) serving as the input switching element is separated from a line for transmitting the clock signal CK (CK bar). This arrangement makes it possible to reduce the load capacity and power consumption of a driving circuit of the clock signal CK (CK bar), for example, the control circuit 5 of FIG. 2.

[0171] Here, in FIG. 38, in the same manner as level shifters 13 and 23, the operation/suspension is controlled by a single control signal ENA; however, the number of the transistors N91 to P94 and the inverter INV91 is increased according to the number of the control signals ENA in the same manner as level shifters 14, 24, and 25, so that the operation/suspension can be controlled by a plurality of the control signals ENA.

[0172] Even when the level shifters 41 having the above constructions are used, a plurality of the level shifters 41 are provided, and at least one of them requiring no clock output is suspended. Therefore, as compared with the construction in which a single level shifter applies a clock signal to all flip flops of a shift register, it is possible to reduce the load capacity of each of the level shifters. Furthermore, power consumption of the shift registers can be smaller.

[0173] However, in the current-driven level shifter 13 (14, 23 to 25: hereinafter, represented by the level shifter 13), a current is continuously applied to the input switching elements (P11 and P12) during the operation. Therefore, even when the level shifter 41 cannot operate because the clock signal CK is lower in an amplitude than a threshold value of the input switching elements (transistors N81 and N82), a voltage of the clock signal CK can be increased without any problems. Moreover, the level shifters 13 are suspended according to the necessity for the clock output; hence, despite that a plurality of the level shifters 13 which consume electricity even when an output is not changed, it is possible to reduce an increase in power consumption. For this reason, a current-driven type level shifter 13 is more preferable than a voltage-driven type.

[0174] Additionally, in Embodiments 3 to 7, the construction is taken as an example in which each of the level shifters (13, 14, and 23 to 25) is provided for every K pieces of flip flops (F1 and F2). However, even when each block differs in the number of the flip flops, it is possible to achieve virtually the same effect as long as the shift registers are divided into a plurality of blocks and the level shifters are respectively provided in the blocks.

[0175] Furthermore, in the present embodiment, the shift register is adopted in an image display apparatus; however, the shift register can be widely adopted as long as the clock signal CK is applied with an amplitude lower than a driving voltage of the shift register. Here, in the case of the image display apparatus, more resolution and a larger display area are strongly demanded, so that a large number of the shift registers are provided and a driving capability of the level shifter cannot be sufficiently secured. For this reason, the shift register with the above construction is particularly effective for a driving circuit of the image display apparatus.

[0176] As described above, a shift register of the present invention, in which a plurality of flip flops are connected, is characterized by including a plurality of level shifters for level-shifting a clock signal, the level shifter being provided for every predetermined number of the flip flops.

[0177] According to the above arrangement, as compared with a construction in which a single level shifter applies a level-shifted clock signal to all flip flops, a distance between the level shifter and the flip flop is smaller. As a result, a distance for transmitting a level-shifted clock signal can be shorter so as to decrease a load capacity of the level shifter and to reduce the need for a driving capability of the level shifter. With this arrangement, for example, even in the case of a small driving capability of the level shifter and a long distance between the ends of the flip flop, it is possible to eliminate the necessity for a buffer between the level shifter and the flip flop so as to reduce power consumption of the shift register.

[0178] Further, in the shift register having the above construction, at least one of a plurality of the level shifters is preferably suspended.

[0179] The above construction makes it possible to reduce power consumption of the shift register as compared with a construction in which all the level shifters are simultaneously operated. As a result, it is possible to achieve the shift register which can operate by a low-voltage input of a clock signal and with small power consumption.

[0180] Moreover, in the shift register having the above construction, it is more desirable that each of the level shifters be operated only when a corresponding block includes the flip flops which require an input of a clock signal at that point.

[0181] According to the above construction, only the level shifter required for transmitting an input pulse is operated. Thus, as compared with the construction in which all the level shifters are operated, it is possible to dramatically reduce power consumption of the shift register. Additionally, a construction is also available in which some of the level shifters are temporarily operated. At least one of the level shifters is temporarily operated, so that power consumption is smaller as compared with the construction in which all the level shifters are continuously operated.

[0182] Further, the shift registers with the above arrangements are also allowed to have a construction in which a specific block of the blocks includes set reset flip flops acting as the above flip flops, that are set in response to the clock signal, and a specific level shifter corresponding to the specific block starts its operation at the start of a pulse input to the specific block, and the specific level shifter stops its operation after the flip flop is set at the final step of the specific block.

[0183] According to the above construction, the specific level shifter applies a level-shifted clock signal if necessary during the operation of the set reset flip flops in the specific block, and when a clock signal input to the set reset flip flop is not necessary, the operation is suspended. As a result, it is possible to reduce power consumption of the level shifters, which include the set reset flip flops as the above flip flops, and operate faster than a construction including D flip flops.

[0184] Furthermore, when the shift register with the above arrangement includes only one of the flip flops (set reset flip flops) in the specific block, the specific level shifter is allowed to start its operation at the start of a pulse input to the specific block, and the specific level shifter is also allowed to suspend its operation at the end of the pulse input.

[0185] According to the above arrangement, to control the operation/suspension of the specific level shifter, an input pulse is used when the specific block is at the first step, and an output of the previous flip flop is used in other cases. Consequently, it is not necessary to provide another circuit for judging an operation period of the specific level shifter, thereby simplifying the construction of the shift register.

[0186] Meanwhile, regarding the shift register with the above arrangement, when the specific block includes a plurality of the flip flops, the specific level shifter can operate during a pulse input to the specific block and during a pulse output performed by one of the flip flops of steps other than the final step of the specific block.

[0187] According to the above arrangement, it is possible to control the operation/suspension of the specific level shifter according to the input to the specific block and the output of the flip flop in the specific block. Here, the operation period can be obtained by, for example, computing an OR of the pulse signals. Hence, for example, as compared with a construction in which a counter for counting the number of the clocks for computing the operation period without using inputs and outputs of the flip flops, it is possible to compute the operation period with a simple circuit. Consequently, it is possible to achieve the simple shift register with a high operation speed.

[0188] Moreover, in the shift register with the above arrangement, when the specific block includes a plurality of the flip flops, the specific level shifter is also allowed to include a latch circuit for changing an output in response to a signal inputted to the specific block and an output signal of the flip flop of the final step in the specific block.

[0189] In the above arrangement, when a signal is inputted to the specific block, the latch circuit changes an output. The specific level shifter starts its operation in response to an output of the latch circuit. Afterwards, the latch circuit maintains the output until the flip flop of the final step outputs a signal. With this arrangement, while a signal is transmitted into the specific block, the specific level shifter continues its operation. Further, when the flip flop of the final step outputs a signal, the latch circuit changes the output so as to suspend the operation of the specific level shifter. Here, the shift register transmits a signal; thus, the operation period of the specific level shifter can be precisely recognized only by monitoring a signal serving as a trigger for the operation/suspension of the specific level shifter, namely, a signal inputted to the specific block and a signal outputted from the flip flop of the final step.

[0190] According to the above arrangement, the output of the latch circuit is changed in response to the two signals serving as triggers for the operation/suspension of the specific level shifter so as to control the operation/suspension of the specific level shifter. Therefore, unlike the construction in which the operation/suspension is controlled in response to a signal outputted from each of the flip flops, it is possible to eliminate the necessity for a complex circuit construction for judging an operation period, even when a large number of the flip flops are provided in the specific block. Consequently, the shift register can be achieved with a simple circuit construction even in the case of a large number of the flip flops.

[0191] On the other hand, the present invention is also applicable to a construction in which a specific block among the blocks includes D flip flops as the above flip flops as well as the construction in which the set reset flip flops are included as the above flip flops. In this case, it is more desirable that the specific level shifter corresponding to the specific block start its operation at the start of a pulse input to the specific block, and the specific level shifter stop its operation at the end of a pulse output of the flip flop of the final step in the specific block.

[0192] According to the above arrangement, the specific block includes the D flip flops as the flip flops. Thus, unlike the construction including the set reset flip flops, it is possible to transmit an input pulse without any problems even when a pulse width (clock number) of the input pulse is changed. Moreover, in the above arrangement, the specific level shifter applies a level-shifted clock signal if necessary during the operation of the D flip flops in the specific block, and the specific level shifter stops its operation when a clock signal does not need to be inputted to the D flip flops. Consequently, it is possible to transmit input pulses having different pulse widths and to realize the shift register achieving small power consumption.

[0193] Additionally, a period from a) a pulse input to the specific block to b) a pulse output from the flip flop of the final step is obtained by, for example, computing an OR of a pulse signal inputted to the specific block and an output signal from the flip flop of each step, and latching a signal serving as a trigger. Therefore, in this case, it is possible to simplify the circuit construction of the shift register as compared with computing an operation period without using the input and output of the flip flop.

[0194] Moreover, in the shift register with the above arrangement, when the specific block includes a plurality of the flip flops, the specific level shifter is also allowed to include a latch circuit for changing an output in response to a signal inputted to the specific block and an output signal from the flip flop of the final step in the specific block.

[0195] According to the above arrangement, the output of the latch circuit is changed in response to the two signals serving as triggers for the operation/suspension of the specific level shifter so as to control the operation/suspension of the specific level shifter. Therefore, unlike the construction in which the operation/suspension is controlled in response to a signal outputted from each of the flip flops, it is possible to eliminate the necessity for a complex circuit construction for judging an operation period even when a large number of the flip flops are provided in the specific block. Consequently, the shift register can be achieved with a simple circuit construction even in the case of a large number of the flip flops.

[0196] Furthermore, in the shift register with the above arrangement, the level shifter is also allowed to include a current-driven level shift section in which input switching elements for applying the clock signal are continuously brought into conduction during the operation.

[0197] According to the above construction, the input switching elements of the level shifter are continuously conducted while the level shifter is operated. Therefore, unlike a voltage-driven level shifter for conducting/shutting off the input switching elements according to a level of the clock signal, even when an amplitude of a clock signal is lower than a threshold voltage of the input switching element, the clock signal can be level-shifted without any problems.

[0198] Furthermore, the current-driven level shifter is larger in power consumption than the voltage-driven level shifter because the input switching elements are brought into conduction during the operation; however, at least one of a plurality of the level shifters suspends its operation. Hence, it is possible to achieve the shift register being able to level-shift even when an amplitude of the clock signal is lower than the threshold voltage of the input switching elements and the shift register consumes smaller electricity than the construction in which all the level shifters are simultaneously operated.

[0199] Also, the shift register with the above arrangement is also allowed to include an input signal control section which applies, as an input signal to the level shift section, a signal at a level for shutting off the input switching elements so as to suspend the level shifter.

[0200] According to the above arrangement, for example, when the input switching elements are MOS transistors, in the case of an input signal applied to the gate, an input signal at a level for shutting off between a drain and a source is applied to the gate so as to shut off the input switching elements. Also, when an input signal is applied to the source, for example, an input signal virtually identical to that of the drain is applied so as to shut off the input switching elements.

[0201] In any one of the above arrangements, when the input signal control section controls a level of an input signal so as to shut off the input switching elements, the current-driven level shifter suspends its operation. With this arrangement, the input signal control section can suspend the level shifter, and during the suspension, power consumption can be reduced by current applied to the input switching elements during the operation.

[0202] Meanwhile, each of the level shifters with the above arrangements is also allowed to include a power supply control section which suspends power supply to each of the level shift sections so as to suspend the level shifter.

[0203] With this arrangement, the power supply control section can suspend the level shifter by interrupting power supply to each of the level shift sections, and during the suspension, power consumption can be reduced by electricity consumed in the level shifters during the operation.

[0204] Incidentally, during the suspension of the level shifter, when an output voltage of the level shifter becomes irregular, the flip flops connected to the level shifter may operate in an unstable manner.

[0205] Therefore, in the shift registers with the above arrangements, it is more desirable that the level shifter include an output stabilizing means for maintaining an output voltage at a predetermined value.

[0206] According to the above arrangement, an output voltage of the level shifter is maintained at a predetermined value by the output stabilizing means. As a result, it is possible to prevent malfunction of the flip flops that is caused by an irregular output voltage, thereby achieving the more stable shift register.

[0207] Furthermore, it is more desirable that each of the shift registers having the above arrangement include a clock signal line where the clock signal is transmitted, and switches which are disposed between the clock signal line and the level shift section and are opened during the suspension of the level shifter. Additionally, the switches can be also provided as a part of the input signal control section.

[0208] According to the above arrangement, unlike the construction in which all the level shifters are continuously connected to the clock signal line and the input switching elements of all the level shift sections act as loads on the clock signal line, only the input switching elements of the level shifters under operation are connected to the clock signal line. Moreover, during the suspension, even when the switch is opened and an input of the level shifter becomes irregular, the output stabilizing means maintains an output of the level shifter at a predetermined value. Therefore, this arrangement does not cause malfunction of the flip flops. Consequently, it is possible to reduce a load capacity of the clock signal line and to realize smaller power consumption of the circuit for driving the clock signal line.

[0209] Meanwhile, in order to solve the aforementioned problems, an image display apparatus of the present invention, which includes a plurality of pixels disposed in a matrix form; a plurality of data signal lines disposed for each row of the pixels; a plurality of scanning lines disposed for each column of the pixels; a scanning signal line driving circuit for successively applying scanning signals with different timings to the scanning signal lines in synchronization with a first clock signal having a predetermined period; and a data signal line driving circuit for extracting data signals from image signals applied to the pixels on the scanning lines where the scanning signals are applied, the image signals being successively applied in synchronization with a second clock signal having a predetermined period, the image signals indicating a display state of each of the pixels, wherein at least one of the data signal line driving circuit and the scanning signal line driving circuit is provided with a shift register having any one of the aforementioned arrangements, in which the first or the second clock signal serves as the clock signal.

[0210] In such an image display apparatus, the more data signal lines, or the more scanning lines, the more flip flops are accordingly provided so as to increase a distance between the ends of the flip flop. However, the shift registers with the aforementioned arrangements make it possible to reduce a buffer and power consumption even in the case of a small driving capability of the level shifter and a long distance between the ends of the flip flop.

[0211] Therefore, at least one of the data signal line driving circuit and the scanning signal line driving circuit is provided with the shift registers according to the aforementioned arrangements so as to realize the image display apparatus achieving small power consumption.

[0212] Namely, an image display apparatus includes a data signal extract means for extracting a data signal corresponding to each of the pixels from an image signal in synchronization with a clock signal; and a data signal output means for outputting the data signal to each of the pixels, wherein a shift register of the present invention is adopted for the data signal extract means so as to realize the image display apparatus achieving small power consumption.

[0213] Further, in the image display apparatus having the above arrangement, it is more desirable that the data signal line driving circuit, the scanning signal line driving circuit, and the pixels be formed on the same substrate.

[0214] According to the above arrangement, the data signal line driving circuit, the scanning signal line driving circuit, and the pixels are formed on the same substrate. Wires between the data signal line driving circuit and the pixels and wires between the scanning signal line driving circuit and the pixels are disposed on the substrate without the need for disposing the wires outside the substrate. As a result, even in the case of a larger number of the data signal lines and the scanning signal lines, it is not necessary to change the number of signal lines disposed outside the substrate, achieving fewer steps for assembling the circuit. Furthermore, it is not necessary to dispose terminals for connecting the signal lines and the outside of the substrate, so that it is possible to prevent an excessive increase in capacities of the signal lines, thereby preventing a decrease in a degree of integration.

[0215] Incidentally, with a polycrystalline silicon thin film, it is more easier to expand a substrate area as compared with a monocrystalline silicon thin film; however, a polycrystalline silicon transistor is inferior in a transistor property such as mobility and a threshold value as compared with a monocrystalline silicon transistor. Therefore, when the monocrystalline silicon transistor is used for manufacturing the circuits, it is difficult to expand a display area; meanwhile, when the polycrystalline silicon thin film transistor is used for manufacturing the circuits, the driving capabilities of the circuits become smaller. Additionally, when the driving circuits and the pixels are formed on the different substrates, it is necessary to connect the substrates via signal lines, resulting in more steps in the manufacturing process and an increase in the capacities of the signal lines.

[0216] For this reason, in the image display apparatus according to the aforementioned arrangements, it is more desirable that the data signal line driving circuit, the scanning line driving circuit, and the pixels include switching elements formed by a polycrystalline silicon thin film transistor.

[0217] According to the above arrangement, the data signal line driving circuit, the scanning line driving circuit, and the pixels include switching elements formed by a polycrystalline silicon thin film transistor so as to readily increase a display area. Furthermore, these members can be readily formed on the same substrate so as to reduce the steps of the manufacturing process and the capacities of the signal lines. Additionally, with the shift registers according to the aforementioned arrangements, a level-shifted clock signal can be applied to each of the flip flops without any problems even in the case of a low driving capability of the level shifter. Consequently, it is possible to realize the image display apparatus achieving small power consumption and a large display area.

[0218] Moreover, in the image display apparatus according to the aforementioned arrangements, it is more desirable that the data signal line driving circuit, the scanning signal line driving circuit, and the pixels include switching elements manufactured at a process temperature of 600 C. or less.

[0219] According to the above arrangement, the process temperature of the switching elements is set at 600 C. or less; thus, even when a normal glass substrate (glass substrate having a deformation point at 600 C. or less) is used as a substrate for each of the switching elements, it is possible to prevent warp and deformation appearing in a process at the deformation point or more. Consequently, it is possible to achieve the image display apparatus which is readily mounted with a larger display area.

[0220] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.