Display apparatus with capacitive light-emitting devices and method of driving the same

[0002] 1. Field of the Invention

[0003] The present invention relates to an image display apparatus and a method for driving the apparatus and, more particularly, to a display apparatus having capacitive light-emitting devices, such as organic electroluminescence devices, and the method for driving the apparatus.

[0004] 2. Description of the Related Art

[0005] An electroluminescence display panel which has a plurality of organic electroluminescence devices arranged in a matrix form is receiving great attention as a display which can have lower power consumption and high display quality and can be suitable for thin-profile display apparatus. As shown in FIG. 1, the organic electroluminescence device has at least a single organic function layer 102, comprised of an electron-transport layer, a light-emitting layer, hole-transport layer, etc., and a metal electrode 103, both formed on a transparent substrate 100 like a glass plate on which a transparent electrode 101 is formed. As a positive voltage is applied to the anode of the transparent electrode 101 and a negative voltage to the cathode of the metal electrode 103, i.e., as a DC voltage is applied between the transparent electrode 101 and the metal electrode 103, the organic function layer 102 emits light. With the organic function layer formed of an organic compound which can be expected to have an excellent emission characteristic, the electroluminescence display can be used practically.

[0006] An organic electroluminescence device (hereinafter also referred to as “EL device”) can be expressed as an electrically equivalent circuit as shown in FIG. 2. As apparent from the circuit diagram, the device can be replaced with a capacitive component C and a component E with a diode characteristic that is coupled in parallel to the capacitive component C. The EL device is thus a capacitive light-emitting device. When a DC drive voltage is applied between the electrodes of the EL device, charges are stored in the capacitive component C. When the drive voltage exceeds the barrier voltage or emission threshold value inherent to the device, a current starts flowing into the organic function layer that has the light-emitting layer from one of the electrodes (the anode side of the diode component E) and light is emitted with the intensity proportional to the current.

[0007] The voltage V v.s. current I v.s. luminance L characteristic of the device is similar to the diode characteristic such that the current I is very small for the voltage equal to or lower than the emission threshold value Vth but abruptly increases when the voltage becomes greater than the emission threshold value Vth, as shown in FIG. 3. The current I is approximately proportional to the luminance L. Such a device provides a luminance proportional to the current that accords to the drive voltage when the drive voltage above the emission threshold value Vth is applied to the device, but it has substantially no drive current flowing when the applied drive voltage is lower than the emission threshold value Vth, so that the luminance stays substantially equal to zero.

[0008] Passive matrix driving can be used to drive a display panel which uses a plurality of such EL devices. FIG. 4 exemplifies the structure of a passive matrix display panel. An N number of cathode lines (metal electrodes) B₁to B_nare laid horizontally, and an M number of anode lines (transparent electrodes) A₁to A_mare laid in parallel vertically to cathode lines B₁-B_n, with light-emitting layers of EL devices E_1,1to E_m,nplaced at (a total of n×m) intersections between the anode lines A₁-A_mand the cathode lines B₁-B_n. The devices E_1,1to E_m,nwhich serve as pixels are arranged in a grid pattern, and have their one ends (each of which corresponds to the anode of the diode component E in the aforementioned equivalent circuit) connected to the anode lines A₁-A_mat the respective intersections between the vertical anode lines A₁-A_mand the horizontal cathode lines B₁-B_nand the other ends (each of which corresponds to the cathode of the diode component E in the equivalent circuit) connected to the cathode lines B₁-B_n. The cathode lines B₁-B_nare connected to, and driven by, a cathode-line scan circuit 1, while the anode lines A₁-A_mare connected to, and driven by, an anode-line driver 2.

[0009] The cathode-line scan circuit 1 has scan switches 5₁to 5_nwhich are associated with the cathode lines B₁-B_nand respectively determine the potentials of the cathode lines B₁-B_n. Each of the scan switches 5₁-5_nconnects either a reverse bias voltage V_CC(e.g., 10 V), which is a power supply voltage, or a ground potential (0 V) to the associated cathode line.

[0010] The anode-line driver 2 has current sources (e.g., constant current sources) 2₁to 2_mand drive switches 6₁to 6_m, which are associated with the anode lines A₁-A_mand supply the drive current to the respective devices via the respective anode lines. The anode-line driver 2 performs ON/OFF control on the drive switches 6₁-6_mto let the current flow through the respective anode lines A₁-A_mindividually. It is typical to use current sources as the drive sources instead of voltage sources like constant voltage sources for reasons such as the aforementioned current v.s. luminance characteristic being stable with respect to a temperature variation whereas the voltage v.s. luminance characteristic is not. The amount of the current to be supplied from each of the current sources 2₁-2_mis set to the amount that is necessary to keep the associated device emitting light at the desired instantaneous luminance (hereinafter this state will be called “steady emission state”). As electrical charges are being stored in the capacitive component C in the device while the device is in the steady emission state, the voltage across the device becomes a specified value Ve (hereinafter called “specified emission voltage”).

[0011] The anode lines A₁-A_mare also connected to an anode-line resetting circuit 3, which has shunt switches 7₁-7_mprovided for the respective anode lines. As each shunt switch is selected, the anode-line resetting circuit 3 sets the associated anode line to the ground potential.

[0012] The cathode-line scan circuit 1, the anode-line driver 2 and the anode-line resetting circuit 3 are connected to an emission controller 4.

[0013] In accordance with image data supplied from an image data generating system (not shown), the emission controller 4 controls the cathode-line scan circuit 1, the anode-line driver 2 and the anode-line resetting circuit 3 to display images carried by the image data. The emission controller 4 controls switching of the scan switches 5₁-5_nto send a scan-line selection control signal to the cathode-line scan circuit 1, select one of the cathode lines that corresponds to the horizontal scan period of the image data, connect the selected cathode line to the ground and apply the reverse bias voltage V_CCto the other cathode lines. The reverse bias voltage V_CCis applied by a constant voltage source to be connected to each cathode line in order to prevent cross-talk emission from the devices connected at the intersections of the driven anode lines and the cathode lines which are not selected for scanning. The reverse bias voltage V_CCis generally set equal to the specified emission voltage Ve. As the scan switches 5₁-5_nare sequentially switched to the ground potential every horizontal scan period, the cathode line which has been switched to the ground potential serves as a scan line which permits the devices connected to the cathode line to emit light.

[0014] The anode-line driver 2 performs drive control on the selected scan line. The emission controller 4 generates drive control signals (drive pulses) indicating which device connected to the scan line should be enabled to emit light at what timing and for how long, in accordance with pixel information specified by the image data, and sends the drive control signal to the anode-line driver 2. In accordance with the drive control signal, the anode-line driver 2 implements ON/OFF control on some of the drive switches 6₁-6_mand supplies the drive current to the devices corresponding to the pixel information via the associated anode lines A₁-A_m. Consequently, the devices supplied with the drive current emit light according to the pixel information.

[0015] The reset operation of the anode-line resetting circuit 3 is performed in response to a reset control signal from the emission controller 4. The anode-line resetting circuit 3 sets any of the shunt switches 7₁-7_mwhich corresponds to the anode line to be reset that is indicated by the reset control signal, and sets off the other shunt switches.

[0016] Japanese Laid-Open Patent Publication (KOKAI) No. H 9-232074 of the same applicant as the present application discloses a driving method of executing a reset operation to discharge electrical charges stored in individual devices laid out in a grid pattern on a passive matrix display panel immediately before changing the scan line (this method will be hereinafter called “reset driving method”). The reset driving method quickens the rising of emission of devices at the time the scan line is changed over to another one. The reset driving method for a passive matrix display panel will now be described with reference to FIGS. 4 to 6.

[0017] The operation exemplified in FIGS. 4 to 6 is for a case where the cathode line B₁is scanned to permit the devices E_1,1and E_2,1to emit light, then scanning is shifted to the cathode line B₂to permit the devices E_2,2and E_3,2to emit light. For easier understanding of the description, the devices which are emitting light are indicated by the symbols of diodes, while the devices which are not emitting light are indicated by the symbols of capacitors. The reverse bias voltage V_CCto be applied to the cathode lines B₁-B_nis 10 V, the same as the specified emission voltage Ve for the devices.

[0018] First, only the scan switch 5₁is switched to the ground potential position and the cathode line B₁is scanned in FIG. 4. The reverse bias voltage V_CCis applied to the other cathode lines B₂-B_nby the scan switches 5₂-5_n. At the same time, the current sources 2₁and 2₂are respectively connected to the anode lines A₁and A₂by the drive switches 6₁and 6₂. The other anode lines A₃-A_mare switched to the ground potential (earth) position of 0 V by the shunt switches 7₃-7_m. In the case of FIG. 4, therefore, only the devices E_1,1and E_2,1are biased in the forward direction, and the drive current flows into those devices from the current sources 2₁and 2₂as shown by the arrows, causing only the devices E_1,1and E_2,1to emit light. In this state, the devices E_3,2to E_m,nwhich are not emitting light and are indicated by hatching are charged to the illustrated polarity.

[0019] The following reset control is executed immediately before scanning is shifted from the steady emission state in FIG. 4 to a state where the next devices E_2,2and E_3,2emit light. Specifically, as shown in FIG. 5, all the drive switches 6₁-6_mand scan switches 5₁-5_nare connected to the voltage V_CCand all the shunt switches 7₁-7_mare opened. When the all-resetting is carried out, all of the anode lines and the cathode lines have the same potential, so that the charges stored in the individual devices are discharged through the routes indicated by the arrows in FIG. 5. As a result, the charges stored in all the devices will vanish instantaneously.

[0020] After the charges stored in all the devices are set to zero, only the scan switch 5₂corresponding to the cathode line B₂is switched to the 0 V position to scan the cathode line B₂as shown in FIG. 6. At the same time, the drive switches 6₂and 6₃are closed to connect the current sources 2₂and 2₃to the associated anode lines, and the shunt switches 7₁and 7₄-7_mare switched on to apply 0 V to the anode lines A₁and A₄-A_m.

[0021] As apparent from the above, the emission control in the reset driving method repeats the scan mode during which one of the cathode lines B₁-B_nis set active and the following reset mode. The scan mode and reset mode are performed every horizontal scan period (1 H) of image data. If the state in FIG. 4 were shifted to the state in FIG. 6 directly without the reset control, the drive current to be supplied from the current source 2₃, for example, not only would flow into the device E_3,2but would also be used to cancel the charges of the opposite polarity (shown in FIG. 4) stored in the devices E_3,3to E_3,n. It would therefore take time to render the device E_3,2in the steady emission state (to set the voltage across the device E_3,2to the specified emission voltage Ve).

[0022] Through the above-described reset control, however, the potentials of the anode lines A₂and A₃become approximately V_CCthe instant scanning is shifted to the cathode line B₂, so that the charge current flow into the devices E_2,2and E_3,2which should emit light next, through a plurality of routes from the constant voltage sources connected to the cathode lines B₁and B₃-B_nas well as from the current sources 2₂and 2₃. The charge current make the voltages across the devices E_2,2and E_3,2reach the specified emission voltage Ve instantaneously, thus enabling instantaneous transition to the steady emission state.

[0023] Since the conventional reset driving method temporarily resets all of the cathode lines and the anode lines by connecting those lines to the ground potential of 0 V or the same potential as the reverse bias voltage V_CCbefore emission control moves to the next scan line, it is possible to speed up charging of the devices to emit light in the next scan to the emission threshold value Vth at the time the scan line is switched and quicken the rising of emission of the devices on the switched scan line which should emit light.

[0024] The charges stored in parallel capacitive components of the devices that are to emit light are discharged before starting each scanning in the passive matrix display panel employing the aforementioned reset driving method. Thus, it has a deficiency that the electrical energy is disadvantageously wasted, particularly when displaying images with low lighting ratio. Paying attention to a case where the EL devices E_m,1and E_m,2connected to the anode line A_mdo not emit light when the scanning target is switched from the cathode line B₁to the cathode line B₂as shown in FIGS. 4 to 6, for example, the power loss of those devices will be explained referring to FIGS. 7A through 7C. As shown in FIG. 7A, while the device E_m,1is not charged during the first scanning of the cathode line B₁due to the cathode line B₁and anode line A_mboth being at the ground potential, the devices E_m,2to E_m,nare biased in the reverse direction with the reverse bias voltage V_CCand their parallel capacitive components are charged with charges Q via the cathode lines B₂-B_n. The total amount of charges of the devices on the anode line A_mwhich are not emitting light becomes (n−1)Q. Next, all-resetting to V_cccauses all the charges (n−1)Q to be discharged via the anode line A_mand cathode lines B₂-B_n, and the charge of the device becomes zero, as shown in FIG. 7B. During the second scanning of the next cathode line B₂, as shown in FIG. 7C, each of the parallel capacitive components of the devices E_m,1and E_m,2to E_m,non the anode line A_mare charged with charges (n−1)Q. When one pays attention to the devices which do not emit light, therefore, wasteful discharging occurs every resetting operation. In other words, in a case where an anode line is reset between the first and second scans and the devices on that anode line, such as the devices E_2,1and E_2,2on the anode line A₂, are rendered off from off, consumed power of charges 2(n−1)Q is wasted. The power loss by the charging and discharging of the parallel capacitive components in a plurality of EL devices of the display panel becomes greater in proportion to the parallel capacitance per unit area and the effective area of the display panel. It is therefore necessary to reduce the power loss.

[0025] Accordingly, it is an object of the present invention to provide a display apparatus with capacitive light-emitting devices, which quickens the rising of light emission without increasing power consumption.

[0026] To achieve the object, according to one aspect of the present invention, there is provided a method for driving a display apparatus with capacitive light-emitting devices including a plurality of capacitive light-emitting devices located at a plurality of intersections of drive lines and scan lines and respectively electrically connected between the scan lines and the drive lines, scan switches for connecting the scan lines when activated to one of a first potential and a second potential different from each other, drive switches for connecting the drive lines to either one of the first or second potential or a drive source when activated, and emission control means for controlling the drive switches and the scan switches, whereby the drive switches are activated so as to selectively connect the drive lines to the drive source to allow selected capacitive light-emitting devices to emit light in synchronism with scan timings at which the scan switches connect the scan lines to a lower one of the first and the second potentials, which method comprises the steps of inserting a reset period between each of scan periods; selecting unconnected drive lines among all of the drive lines which are not connected to the drive source in a present scan period in the reset period; and connecting all of the scan lines to the same reset potential, connecting the selected unconnected drive lines to a ground potential, and connecting the other drive lines to the reset potential in the reset period.

[0027] According to a second aspect of the present invention, there is provided a method for driving a display apparatus with capacitive light-emitting devices including a plurality of capacitive light-emitting devices located at a plurality of intersections of drive lines and scan lines and respectively electrically connected between the scan lines and the drive lines, scan switches for connecting the scan lines when activated to one of a first potential and a second potential different from each other, drive switches for connecting the drive lines to either one of the first or potential different from each other when activated, and emission control means for controlling the drive switches and the scan switches, whereby the drive switches are activated so as to selectively connect the drive lines to the drive source to allow selected capacitive light-emitting devices to emit light in synchronism with scan timings at which the scan switches connect the scan lines to a lower one of the first and the second potentials, which method comprises the steps of inserting a reset period between each of scan periods; selecting non-connection keeping drive lines among all of the drive lines which are not connected to the drive source in a previous scan period and a present scan period in the reset period; and connecting all of the scan lines to the same reset potential, connecting the selected non-connection keeping drive lines to the ground potential and connecting the other drive lines to the reset potential in the reset period.

[0028] In the method according to the present invention, the selection of the unconnected drive lines or the non-connection keeping drive lines is carried out in a reset period immediately before the present scan period.

[0029] In the method according to the present invention, one of the first potential and the second potential is a ground potential, while the other one is a potential greater than a potential difference between a specified emission voltage of the capacitive light-emitting devices and an emission threshold voltage.

[0030] In the method according to the present invention, one of the first potential and the second potential is a ground potential, while the other one is approximately equal to a specified emission voltage of the capacitive light-emitting devices.

[0031] In the method according to the present invention, the reset potential is equal to one of the first and second potentials which has a higher potential.

[0032] In the method, the scan line to which the selected capacitive light-emitting devices are connected is connected to the ground potential, and the other scan lines are connected to a potential greater than the potential difference between the specified emission voltage of the capacitive light-emitting devices and the emission threshold voltage in the scan period.

[0033] In the method, the scan line to which the selected capacitive light-emitting devices are connected is connected to the ground potential, and the other scan lines are connected to a potential approximately equal to the specified emission voltage of the capacitive light-emitting devices in the scan period.

[0034] In the method, drive lines other than the drive line to which the selected capacitive light-emitting devices are connected are connected to the ground potential in the scan period.

[0035] In the method according to the first or second aspect, the capacitive light-emitting devices are electroluminescence devices.

[0036] In the method according to the present invention, the capacitive light-emitting devices are located at intersections of a plurality of drive lines extending approximately in parallel to one another and a plurality of scan lines extending approximately perpendicularly to the drive lines and approximately in parallel to one another and respectively electrically connected between the scan lines and the drive lines.

[0037] Further, according to a third aspect of the present invention, there is provided a display apparatus with capacitive light-emitting devices; comprises a plurality of capacitive light-emitting devices located at a plurality of intersections of drive lines and scan lines and respectively electrically connected between the scan lines and the drive lines; scan switches for connecting the scan lines to one of a first potential and a second potential different from each other when activated; drive switches for connecting the drive lines to either one of the first or potential different from each other when activated; emission control means for controlling the drive switches and the scan switches in such a way that the drive switches are activated so as to connect the drive lines to the drive source to allow selected capacitive light-emitting devices to emit light in synchronism with scan timings at which the scan switches connects the scan lines to a lower one of the first and the second potentials; and discrimination means for selecting unconnected drive lines among all of the drive lines which are not connected to the drive source in a present scan period, whereby the emission control means provides a reset period between each of scan periods, and performs such control as to connect all of the scan lines to the same reset potential, to connect the unconnected drive lines selected by the discrimination means to the ground potential and to connect the other drive lines to the reset potential in the reset period.

[0038] According to a fourth aspect of the present invention, there is provided a display apparatus with capacitive light-emitting devices; comprises a plurality of capacitive light-emitting devices located at a plurality of intersections of drive lines and scan lines and respectively electrically connected between the scan lines and the drive lines; scan switches for connecting the scan lines to one of a first potential and a second potential different from each other when activated; drive switches for connecting the drive lines to either one of the first or potential different from each other when activated; emission control means for controlling the drive switches and the scan switches in such a way that the drive switches are activated so as to connect the drive lines to the drive source to allow selected capacitive light-emitting devices to emit light in synchronism with scan timings at which the scan switches connect the scan lines to a lower one of the first and the second potentials; and discrimination means for selecting non-connection keeping drive lines among all of the drive lines which are not connected to the drive source in a previous scan period and a present scan period, whereby the emission control means provides a reset period between each of scan periods, connects all of the scan lines to the same reset potential, connects the non-connection keeping drive lines selected by the discrimination means and connects the other drive lines to the reset potential in the reset period.

[0039] Thus, according to the present invention, in contrast to the so-called reset driving method, not all the drive lines are set to the same potential in a reset period, but any drive line which is not connected to the drive source in both the previous and present scan periods or any drive line which is not connected to the drive source in the present scan period is discriminated. The unselected drive lines are connected to the reset potential, while the selected drive lines are connected to the ground potential, not to the reset potential, so that the residual charges in the capacitive components of the devices on the drive lines can be held undischarged. Further, it is possible to avoid charging of the non-emitting devices, which charging does not contribute to light emission. It is therefore possible to provide a display apparatus with capacitive light-emitting devices, which quickens the rising of light emission without increasing power consumption.

[0040] FIG. 1 is a cross-sectional view of an organic electroluminescence (EL) device;

[0041] FIG. 2 is a diagram showing an equivalent circuit of an EL device;

[0042] FIG. 3 is a graph schematically showing the drive voltage v.s. luminance characteristic of an EL device;

[0043] FIG. 4 is a block diagram for explaining the structure of a display apparatus which uses conventional EL devices and a 0-V (0 Volt) reset driving method which is adapted for the display apparatus;

[0044] FIG. 5 is a block diagram for explaining the structure of the display apparatus which uses conventional EL devices and the 0-V reset driving method which is adapted for the display apparatus;

[0045] FIG. 6 is a block diagram for explaining the structure of the display apparatus which uses conventional EL devices and the 0-V reset driving method which is adapted for the display apparatus;

[0046] FIGS. 7A through 7C are schematic circuit diagrams for explaining the structure of the display apparatus which uses conventional EL devices and the 0-V reset driving method which is adapted for the display apparatus;

[0047] FIG. 8 is a block diagram for explaining the structure of a display apparatus having EL devices according to the present invention;

[0048] FIG. 9 is a flowchart illustrating a first mode of a reset driving method for the display apparatus according to the present invention;

[0049] FIG. 10 is a flowchart illustrating a second mode of the reset driving method for the display apparatus according to the present invention;

[0050] FIG. 11 is a block diagram for explaining the structure of a display apparatus having EL devices according to an embodiment of the present invention, and a V_cc/0V reset driving method which is adapted for the display apparatus;

[0051] FIG. 12 is a block diagram for explaining the structure of the display apparatus having EL devices according to the embodiment of the present invention, and the V_cc/0V reset driving method which is adapted for the display apparatus;

[0052] FIG. 13 is a block diagram for explaining the structure of the display apparatus having EL devices according to the embodiment of the present invention, and the V_cc/0V reset driving method which is adapted for the display apparatus;

[0053] FIG. 14 is a block diagram for explaining the structure of a display apparatus having EL devices according to another embodiment of the present invention, and a V_cc/0V reset driving method which is adapted for the display apparatus;

[0054] FIG. 15 is a block diagram for explaining the structure of the display apparatus having EL devices according to another embodiment of the present invention, and the V_cc/0V reset driving method which is adapted for the display apparatus; and

[0055] FIG. 16 is a block diagram for explaining the structure of the display apparatus using EL devices according to another embodiment of the present invention, and the V_cc/0V reset driving method which is adapted for the display apparatus.

[0056] Preferred embodiments of the present invention will now be described referring to the accompanying drawings.

[0057] FIG. 8 is a block diagram for explaining the structure of a display apparatus according to the present invention, which uses organic electroluminescence EL devices (hereinafter simply referred to as “EL device”). The display apparatus has a capacitive light-emitting panel 120 and an emission controller 40. The light-emitting panel 120 comprises a plurality of EL devices E_i,j(1≦i≦m, 1≦j≦n) arranged in a matrix form at the intersections of drive lines like the aforementioned anode lines A₁-A_mand scan lines like the aforementioned cathode lines B₁-B_n. Each of the devices are connected electrically between the associated scan line and drive line. That is, the EL devices are located at the intersections of a plurality of drive lines extending approximately in parallel to one another and a plurality of scan lines extending approximately perpendicularly to the drive lines and approximately in parallel to one another and connected to the respective scan lines and drive lines. The light-emitting panel 120 includes a cathode-line scan circuit 1 or scan switches for connecting the scan lines to one of a ground potential and a reverse bias potential V_cc(this is the reset potential) different from each other when activated, and an anode-line driver 2 or drive switches for connecting the drive lines to at least one of the ground potential and the reset potential (reverse bias potential V_cc) or to a drive source when activated.

[0058] As shown in FIG. 10, the cathode-line scan circuit 1 has scan switches 5₁to 5_nwhich are associated with the respective cathode lines B₁-B_nand each of which connects either a reverse bias voltage V_CC(e.g., 10 V), which is the supply voltage, or the ground potential (0 V) to the associated cathode line. The anode-line driver 2 has current sources 2₁to 2_mwhich are associated with the anode lines A₁-A_mand three-position drive switches 6₁to 6_m, which switch to either the current sources 2₁-2_m, the reset potential or the ground potential. The anode-line driver 2 performs ON/OFF control on the drive switches 6₁-6_mto let the current flow through the respective anode lines A₁-A_mindividually. Therefore, the reverse bias voltage V_CCshould be made greater than the difference, Ve−Vth (Ve: the specified emission voltage, Vth: emission threshold value) to prevent unselected devices from erroneously emitting light. As mentioned above, the reverse bias voltage V_CCis generally set equal to the specified emission voltage Ve.

[0059] The cathode-line scan circuit 1 performs switch control according to the so-called line-sequential scanning of sequentially switching the cathode lines B₁-B_nto the ground potential every horizontal scan period and switching them to the reverse bias voltage V_CCin the other periods by using the scan switches. The cathode-line scan circuit 1 may execute interlace scan control instead of the line-sequential scanning. Image data is supplied to the anode lines A₁-A_mvia the drive switches of the anode-line driver 2. Accordingly, the cathode lines serve as scan lines to enable the devices connected thereto to emit light, and the anode lines serve as drive lines to cause the devices connected thereto to emit light.

[0060] The emission controller 40, connected to the cathode-line scan circuit 1 and the anode-line driver 2, serves as emission control means which controls both circuits. The emission controller 40 allows the anode-line driver 2 to selectively connect the drive lines to the respective drive sources, causing the selected devices to emit light, in synchronism with the cyclic scan period in which the cathode-line scan circuit 1 connects one of the scan lines to the ground potential.

[0061] In the emission controller 40, a sync separator circuit 41 extracts horizontal and vertical sync signals from an input video signal supplied, and sends those sync signals to a timing pulse generator 42. The timing pulse generator 42 generates a sync signal timing pulse based on the extracted horizontal and vertical sync signals, and sends the timing pulse to an A/D (Analog-to-Digital) converter 43, a control circuit 45 and a scan timing signal generator 47. The A/D converter 43 converts the input video signal to digital pixel data corresponding to one pixel in synchronism with the sync signal timing pulse, and sends the pixel data to a memory 44. The control circuit 45 sends a write signal and read signal synchronous with the sync signal timing pulse to the memory 44 based on a driving method which will be discussed later. The memory 44 sequentially fetches individual pieces of pixel data supplied from the A/D converter 43 in accordance with the write signal. In accordance with the read signal, the memory 44 sequentially reads the stored pixel data and send the data to an output processor 46. The scan timing signal generator 47 generates various kinds of timing signals to control the scan switches and drive switches and send those timing signals to the cathode-line scan circuit 1 and the output processor 46 in the next stage. The output processor 46 sends the pixel data supplied from the memory 44 to the anode-line driver 2 in synchronism with the timing signal from the scan timing signal generator 47.

[0062] A first mode of a driving method for the capacitive light-emitting panel which is employed by the emission controller 40 will now be described referring to FIG. 9.

[0063] First, the control circuit 45 determines if an H sync pulse indicative of one horizontal scan period (1H) has reached the memory 44 (step 1).

[0064] Next, the control circuit 45 fetches image data for the present one horizontal scan period (the j-th scan) from the memory 44 and stores it (step 2).

[0065] Then, the control circuit 45 compares the image data for the previous one horizontal scan period that has been stored at the time of the previous scan (the j-1-th scan), with the image data for the present one horizontal scan period (the j-th scan), and determines if there is any drive line i for which the device connected thereto in the previous scan period (the j-1-th scan) did not emit light and the device connected thereto in the present scan period (the j-th scan) neither emit light (step 3).

[0066] If it is determined that such a drive line i exists, the control circuit 45 returns image data for the j-th horizontal scan to the memory 44, and controls the drive switches of the anode-line driver 2 via the output processor 46 so as to connect the drive line i to the ground potential and set the other drive lines to the reset potential position. This causes all the drive lines except the drive line i and all the scan lines to connect to the same reset potential and connect the drive line i to the ground potential only for the reset time (step 4).

[0067] If it is determined in step 3 that there is no drive line i for which the device connected thereto in the previous scan period (the j-1-th scan) did not emit light and the device connected thereto in the present scan period (the j-th scan) neither emit light, all the drive lines and all the scan lines are connected to the same reset potential only for the reset time (step 5).

[0068] After the above reset mode is completed, a predetermined current is supplied to the drive lines that cross the j-th scan line in accordance with the pixel data for the present horizontal scan period (the j-th scan) (step 6).

[0069] A second mode of a driving method for the capacitive light-emitting panel which is employed by the emission controller 40 will now be described referring to FIG. 10.

[0070] First, as shown in FIG. 10, the control circuit 45 executes steps 1 and 2 in the same way as done in the first mode.

[0071] Then, the control circuit 45 determines if there is any drive line i for which the device connected thereto in the present scan period (the j-th scan) does not emit light (step 3′).

[0072] If it is determined that the drive line i exists, the control circuit 45 controls the drive switches of the anode-line driver 2 via the output processor 46 so as to connect the drive line i to the ground potential and set the other drive lines to the reset potential position (step 4).

[0073] If it is determined in step 3 that there is no drive line i for which the device connected thereto in the present scan period (the j-th scan) does not emit light, all the drive lines and all the scan lines are connected to the same reset potential only for the reset time (step 5). After the reset mode is completed, a predetermined current is supplied to the drive lines in accordance with the pixel data for the present horizontal scan period (the j-th scan) (step 6).

[0074] A first embodiment of the present invention, which is associated with the first mode of the reset driving method for a passive matrix display panel, will be discussed below referring to FIGS. 11 through 13. In the following operation, after the devices E_1,1to E_2,1are allowed to emit light in the first scan (the previous scan) of the cathode line B₁, the devices E_2,2to E_3,2are allowed to emit light in the second scan (the present scan) of the cathode line B₂, as per the prior art (the same symbolic notation will be used). The reverse bias voltage V_CCthat is applied to the cathode lines B₁-B_nis set equal to the specified emission voltage Ve of the devices. The reset potential is the ground potential.

[0075] First, in the first scan period, only the scan switch 5₁is switched to the ground potential position, the cathode line B₁is scanned, and the reverse bias voltage V_CCis applied to the other cathode lines B₂-B_nby the scan switches 5₂-5_nin FIG. 11. At the same time, the current sources 2₁and 2₂are connected to the anode lines A₁and A₂via the drive switches 6₁and 6₂, while the other anode lines A₃-A_mare switched to the ground potential position via the drive switches 6₃-6_m. Therefore, only the devices E_1,1and E_2,1emit light, and at the same time the devices E_3,2to E_3,n, . . . , and E_m,2to E_m,nare charged with the charges Q in the reverse direction as illustrated.

[0076] In the reset period, the emission controller 40 has selected the drive (anode) lines A₄-A_mon which there are no devices that should emit light in the first and second scan periods through the driving method illustrated in FIG. 9. Thus, the emission controller 40 switches the drive switches 6₄-6_mto the ground potential position, switches the drive switches 6₁, 6₂and 6₃to the reverse bias potential position, and switches all the scan switches 5₁-5_nto the reverse bias potential position, as shown in FIG. 12. As the resetting is implemented, the forward charges (i.e., charges in the forward direction) stored in the devices E_1,1and E_2,1and the reverse charges (i.e., charges in the reverse direction) stored in the devices E_3,2to E_3,nare all discharged, and the devices E_4,1, . . . , and E_m,1are charged with the reverse charges Q along the routes indicated by the arrows in the diagram. The devices E_4,2to E_4,n, . . . , and E_m,2to E_m,nkeep holding the reverse charges Q without being charged nor being discharged.

[0077] Then, in the second scan period, only the scan switch 5₂on the cathode line B₂is switched to the ground potential position, the other scan switches are switched to the reverse bias voltage V_CCto scan the cathode line B₂, and at the same time, the drive switches 6₂and 6₃are switched to the current sources 2₂and 2₃while the other drive switches 6₁-6_mare switched to the ground potential position, as shown in FIG. 13. Consequently, the charge current flow into the devices E_2,2and E_3,2that should emit light through a plurality of routes from the constant voltage sources connected to the cathode lines B₁and B₃-B_nas well as from the current sources 2₂and 2₃as per the prior art (see FIG. 6). The charge current can ensure instantaneous transition to the steady emission state. The current likewise flow into the devices E_1,1, E_1,3to E_1,nfrom the constant voltage sources of the reverse bias voltage V_CC, and are charged with the reverse charges Q, as per the prior art (see FIG. 6). As the devices E_4,1, E_4,3to E_4,n, . . . , E_m,1, and E_m,3to E_m,non the respective anode lines A₄, . . . , and A_mare not charged or discharged and those devices keep holding the state in which the charge Q is in the reverse direction. The charges held in the devices E_4,2, . . . , and E_m,2are discharged. Although the other devices than the devices E_2,2and E_3,2that should emit light are also charged along the routes indicated by the arrows in the diagram, they will not emit light erroneously because their charging direction is the reverse bias direction.

[0078] With regard to the consumed charges in the above scan switching operation, the amount of discharged charges at the reset operation and the amount of charged charges at the scan switching operation from/to the devices E_4,1to E_4,n, . . . , and E_m,1to E_m,nare significantly reduced, which means that consumption of charges by the capacitive components of the devices that do not contribute to light emission is reduced greatly, as compared with those in the prior art (FIGS. 4 to 6).

[0079] A reset driving method according to a second embodiment of the present invention, which is also associated with the aforementioned second mode, is illustrated in FIGS. 14 through 16. The second embodiment is for a case where the reset potential is set equal to the ground potential, and the structure of the light emitting panel 120 is the same as the one shown in FIGS. 11 to 13.

[0080] Since the first scan mode illustrated in FIG. 14 is the same as the one shown in FIG. 11, its detailed description will not be repeated. In the reset period, the emission controller 40 has selected the drive (anode) lines A₁and A₄-A_mon which there are no devices that should emit light in the second scan period through the driving method illustrated in FIG. 10. Thus, the emission controller 40 switches the drive switches 6₁and 6₄-6_mto the ground potential position, switches the drive switches 6₂and 6₃to the reverse bias voltage V_CC, and switches all the scan switches 5₁-5_nto the reverse bias voltage V_CC, as shown in FIG. 15.

[0081] When the resetting is carried out, the forward charges stored in the device E_2,1and the reverse charges stored in the devices E_3,2to E_3,nare all discharged, all the devices E_1,1to E_1,nconnected to the anode line A₁, and the devices E_4,1, . . . , and E_m,1are charged with the reverse charges Q. The devices E_4,2to E_4,n, . . . , and E_m,2to E_m,nkeep holding the reverse charges Q without being charged or discharged.

[0082] Thereafter, in the second scan period, as shown in FIG. 16, only the scan switch 5₂on the cathode line B₂is switched to the ground potential position, the other scan switches are switched to the reverse bias voltage V_CCto scan the cathode line B₂, and at the same time, the drive switches 6₂and 6₃are switched to the current sources 2₂and 2₃while the other drive switches are switched to the ground potential position, as in the case shown in FIG. 12.

[0083] Consequently, the charge current flow into the devices E_2,2and E_3,2that should emit light through a plurality of routes from the constant voltage sources connected to the cathode lines B₁and B₃-B_nas well as from the current sources 2₂and 2₃as per the prior art (see FIG. 6). The charge current can ensure instantaneous transition to the steady emission state. The devices E_1,1and E_1,3to E_1,non the anode line A₁keep holding the reverse charges without being charged or discharged. Likewise, the devices E_4,1, E_4,3to E_4,n, . . . , E_m,1,and E_m,3to E_m,non the respective anode lines A₄, . . . , and A_mkeep holding the reverse charges without being charged or discharged.

[0084] With regard to the consumed charges in the above scan switching operation, the amount of discharged charges at the reset operation and the amount of charged charges at the scan switching operation from/to the devices E_4,1to E_4,n, . . . , and E_m,1to E_m,nare significantly reduced, which means that consumption of charges by the capacitive components of the devices that do not contribute to light emission is greatly reduced, as compared with those in the prior art (FIGS. 4 to 6). Since, in the embodiment, the anode lines that should be connected to the ground potential in reset mode is discriminated based only on image data for the present horizontal scan period (the j-th scan), the steps and means needed for the discrimination can be made simpler than the first mode.

[0085] It is also possible to set the reset potential equal to the reverse bias voltage V_CCin the second mode. Although the cathode lines are laid horizontally and the anode lines vertically, their lying directions may be reversed. Although scanning is conducted with the electrodes that are laid horizontally and luminance is controlled with the electrodes that are laid vertically, scanning may be conducted with the vertically-laid electrodes and luminance may be controlled with the horizontally-laid electrodes. In the case of scanning with the anode lines, however, the drive sources of the anode lines and those of the cathode lines should be of the opposite polarities to those mentioned in the foregoing description.

[0086] According to the present invention, as specifically described above, provided is a method for driving a display apparatus with capacitive light-emitting devices which includes a plurality of capacitive light-emitting devices located at a plurality of intersections of drive lines and scan lines and respectively electrically connected between the scan lines and the drive lines, scan switches for connecting the scan lines to one of a first potential and a second potential different from each other when activated, drive switches for connecting the drive lines to either one of the first or second potential or a drive source when activated, and emission control means for controlling the drive switches and the scan switches, whereby the drive switches are activated so as to selectively connect the drive lines to the drive source to allow selected capacitive light-emitting devices to emit light in synchronism with scan timings at which the scan switches connect the scan lines to a lower one of the first and the second potentials. The method includes the steps of; (1) selecting non-connection keeping drive lines among all of the drive lines which are not connected to the drive source in a previous scan period and a present scan period, in the reset period, connecting all of the scan lines to the same reset potential and connecting the selected non-connection keeping drive lines to the ground potential while connecting the other drive lines to the reset potential, or (2) selecting unconnected drive lines among all of the drive lines which are not connected to the drive source in a present scan period, in the reset period, connecting all of the scan lines to the same reset potential and connecting the selected unconnected drive lines to the ground potential while connecting the other drive lines to the reset potential. The present invention can therefore provide a display apparatus with capacitive light-emitting devices, which quickens the rising of light emission without increasing power consumption.

[0087] Although several preferred embodiments of the present invention have been described herein, it should be apparent to those skilled in the art that the present invention may be embodied and modified in many other specific forms without departing from the spirit or scope of the present invention. All of such embodiments and modifications are to be considered as being included within the scope and equivalence of the appended claims.