Image pickup apparatus

[0001] 1. Field of the Invention

[0002] The present invention relates to an image pickup apparatus and an image pickup system using the same and, more particularly, to an image pickup apparatus in which a plurality of photoelectric conversion portions are arranged in a common circuit and an image pickup system using this apparatus.

[0003] 2. Related Background Art

[0004] Digital broadcasting has started in the U.S.A in 1998. In 2006, NTSC broadcasting (525V) will be obsolete and TV broadcasting will completely shift to HD digital. In addition, digital cameras with 1,300,000 pixels are sweeping over the market. This means that there is a demand for outputting high- and low-resolution signals from a high pixel count sensor as needed.

[0005] Under these circumstances, the pixel size in CCDs is shrinking (reducing). However, a CCD with a side of about 5 μm is incapable of high-speed read. CCDs currently commercially available have only 600,000 pixels and a read rate of about 60 frame/sec.

[0006] CMOS sensors manufactured by the same process as the CMOS manufacturing process allow random access and have been expected as sensors suitable for higher-speed operation in the future.

[0007] When a small number of pixels are to be read out from a high pixel count sensor, low pixel count information can be obtained by interlaced scanning. In this interlaced scanning,

• [0008] (1) A CCD discards pixel signals of unnecessary horizontal lines to an overflow drain provided in a horizontal shift register. Additionally, of signals read out from the CCD, only necessary signals are sampled.
• [0009] (2) A CMOS sensor outputs only necessary signals by random access.

[0010] However, interlaced scanning (1) of the CCD requires excess power to transfer charges of unnecessary pixels. In addition, since unnecessary signals are discarded by decimation, moiré due to low sampling rate occurs. Interlaced scanning (2) also generates moiré.

[0011] It is an object of the present invention to provide an image pickup apparatus capable of adding signals from a plurality of photoelectric conversion portions.

[0012] In order to achieve the above object, according to an aspect of the present invention, there is provided an image pickup apparatus comprising a plurality of unit cells arranged in an array, each unit cell including a plurality of photoelectric conversion portions and a common circuit for inputting signals from the plurality of photoelectric conversion portions and outputting the signals from the unit cell, first addition means for adding the signals from the plurality of photoelectric conversion portions in the unit cell, and second addition means for adding the signals from the plurality of photoelectric conversion portions outside the unit cell.

[0013] According to another aspect of the present invention, there is provided an image pickup apparatus comprising a plurality of unit cells arranged in an array, each unit cell including a plurality of photoelectric conversion portions and a common circuit for inputting signals from the plurality of photoelectric conversion portions and outputting the signals from the unit cell, and addition means for adding the signals from the plurality of photoelectric conversion portions for outputting signals of the same color outside the unit cell.

[0014] According to still another aspect of the present invention, there is provided an image pickup apparatus comprising a plurality of unit cells arranged in an array, each unit cell including a plurality of photoelectric conversion portions and a common circuit for inputting signals from the plurality of photoelectric conversion portions and outputting the signals from the unit cell, and addition switching means for arbitrarily switching the signals from the photoelectric conversion portions, which are to be added in the cell.

[0015] The other objects, features, and advantages will become apparent from the following specification in conjunction of the drawings.

[0042] Before a description of the embodiments, the difference between the present invention and prior art will be described.

[0043] When the image of a dark object is to be picked up, a current CMOS sensor adds signals of two vertical pixels. For example, in FIG. 4 of Japanese Patent Application Laid-open No. 9-46596, signals of two photoelectric conversion portions in the vertical direction are added in a cell at the same time. However, there is neither disclosure about addition of signals from photoelectric conversion portions in the horizontal direction nor disclosure about addition of signals from photoelectric conversion portions in the vertical or oblique direction by a horizontal transfer means. Also, there is no disclosure about addition and read of signals of the same color in adding and reading out color signals.

[0044] An arrangement in which one amplification means is prepared for the photoelectric conversion portions of a vertical array of two or three or more pixels is disclosed in Japanese Patent Application Laid-open No. 4-461. An arrangement in which one amplification means is prepared for the photoelectric conversion portions of four pixels in the horizontal and vertical directions is disclosed in Japanese Patent Application Laid-open No. 63-100879. Both prior arts have no disclosure about addition processing.

[0045] FIG. 1 is a schematic view showing the arrangement of part of an image pickup apparatus according to the first embodiment of the present invention. FIG. 2 is a view showing the arrangement of a unit cell S of the image pickup apparatus shown in FIG. 1.

[0046] As shown in FIG. 2, the unit cell S is formed by arranging four photoelectric conversion portions (a₁₁, a₁₂, a₂₁, and a₂₂) for one common amplifier. The remaining unit cells have the same arrangement as that of the unit cell. The common amplifier comprises an amplification means MSF, reset means MRES, and select means MSEL. The input portion of the common amplifier corresponds to the gate portion of the amplification means MSF.

[0047] Lines for controlling signal transfer for two upper photoelectric conversion portions (a₁₁ and a₁₂) of the four pixels, that are adjacent to each other in the horizontal direction are connected to an odd vertical shift register V_o (V_o1, V_o2, V_o3 . . . ). Lines for controlling signal transfer for two lower photoelectric conversion portions (a₂₁ and a₂₂) that are adjacent to each other in the horizontal direction are connected to an even-numbered vertical shift register V_e (V_e1, V_e2, V_e3, . . . ). The reset switch MRES and select switch MSEL of the common amplifier are connected to the corresponding vertical shift registers V_o and V_e through an odd selection circuit S_o and an even selection circuit S_e, respectively. The vertical shift registers V_o and V_e and selection circuits S_o and S_e can be independently controlled.

[0048] FIGS. 3A and 3B are timing charts of the vertical shift register in interlaced scanning. FIG. 3A is a timing chart of odd fields. FIG. 3B is a timing chart of even fields.

[0049] Referring to FIG. 3A, horizontal scanning is performed in units of two lines connected to a common amplifier. More specifically, vertical shift registers V_on of odd rows and vertical shift registers V_en of even rows are simultaneously controlled. The high-level period of signals φ_o and φ_e corresponds to the horizontal blanking period in which the sensor read and reset operations are performed.

[0050] Referring to FIG. 3B, pixels of two lines connected to common amplifiers, which are adjacent to each other between the common amplifiers are selected and horizontally scanned. More specifically, the cell numbers are shifted by one with respect to FIG. 3A, and a combination of a vertical shift register V_on+1 and vertical shift register V_en and a combination of a vertical shift register V_on+2 and vertical shift register V_en+1 are driven.

[0051] In the above interlaced scanning, when pixel signals are to be added, and signals from a plurality of photoelectric conversion portions in one unit cell are to be added, the input portion of one common amplifier can add the signals. However, when signals from a plurality of photoelectric conversion portions in different unit cells are to be added, the signals cannot be added by the input portion of one common amplifier. This will be described with reference to FIG. 4 showing the unit cells of the image pickup apparatus. For addition in the same unit cell, for example, signals from horizontal arrays of photoelectric conversion portions (a₁₁+a₁₂, a₂₁+a₂₂, a₃₁+a₃₂, . . . ), signals vertical arrays of from photoelectric conversion portions (a₁₁+a₂₁, a₃₁+a₄₁, . . . ), or signals from oblique arrays of photoelectric conversion portions (a₁₁+a₂₂, a₃₁+a₄₂, . . . or a₁₂+a₂₁, a₃₂+a₄₁, . . . ) can be added by the same common amplifier A and read out from the unit cell. However, for addition between different unit cells, for example, signals from vertical arrays of photoelectric conversion portions (a₂₁+a₃₁, a₄₁+a₅₁ . . . ), or signals from oblique arrays of photoelectric conversion portions (a₂₁+a₃₂, a₄₁+a₅₂, . . . or a₂₂+a₃₁, a₄₂+a₅₁, . . . ) cannot be added by the same common amplifier A and read out from the unit cell.

[0052] In this embodiment, when an image pickup apparatus which has an array of a plurality of unit cells each having a plurality of photoelectric conversion portions and a common amplifier for receiving signals from the photoelectric conversion portions includes a mode for adding signals from a plurality of photoelectric conversion portions in different unit cells, signals from a vertical or oblique array of photoelectric conversion portions are added using a horizontal transfer means.

[0053] An embodiment of the present invention will be described below in detail.

[0054] Color separation using a color sensor will be described first. FIG. 5 shows unit cells having a color filter in which G pixels are laid out in a checkerboard pattern.

[0055] As shown in FIG. 5, in each of repeated unit cells 30 each comprised of four pixels, G (green) pixels that most influence the resolution are located at the upper left and lower right. Each G pixel has a light-shielding portion 35 at a position line-symmetric with respect to the area of a common amplifier portion 32 at the center of the unit cell 30. Hence, the center of gravity of a photoelectric conversion portion 31 of the G pixel is present at the center of the G pixel. Photoelectric conversion portions a₁₁ and a₂₂ of the G pixels line up at an equal interval a in the vertical and horizontal directions. An R (red) pixel is located at the upper right of each unit cell 30, and a B (blue) pixel is at the lower left of the unit cell 30. These pixels have no particularly designed light-shielding portion, unlike the G pixels, and line up at an equal interval corresponding to an interval 2a of the unit cells 30 because each unit cell 30 has one R pixel and one B pixel.

[0056] FIG. 6 is a timing chart showing color signal read using a color filter in which G pixels are laid out in a checkerboard pattern and R and B pixels are line-sequentially laid out. FIG. 7 is a circuit diagram for reading color signals. FIG. 7 also shows an addition means for adding signals of the same color in a low pixel count signal read (to be described later).

[0057] Referring to FIG. 6, in a period T₁, the vertical signal line is reset by a pulse φ_RV to remove residual charges on the signal line. Simultaneously, the residual charges on temporary storage capacitances C_TN1, C_TN2, C_TN3, C_TN4, C_TS1, C_TS2, C_TS3, and C_TS4 are removed by pulses φ_TN1, φ_TN2, φ_TN3, φ_TN4, φ_TS1, φ_TS2, φ_TS3, and φ_TS4, respectively.

[0058] In a period T₂, as preprocessing for transfer of photoelectric conversion signals of G₁ pixels (G pixel at the upper left in FIG. 5) in the photoelectric conversion portions (a₁₁, a₁₂, . . . , a_1n) of the first row, the gate portion (input portion) of the amplification means MSF of each common amplifier is reset by a pulse φ_oR to remove residual charges. After removal, reset noise remains in the gate portion.

[0059] In a period T₃, the reset noise and the offset voltage of the common amplifier in the period T₂ are transferred to the capacitance C_TN1. The output portion of each common amplifier is connected to the vertical signal line in accordance with a pulse φ_oS, a load MOS transistor is turned on in accordance with a pulse φ_L to operate the common amplifier, and the vertical signal line and capacitance C_TN1 are connected in accordance with the pulse φ_TN1. Noise (N₁) is stored in the capacitance C_TN1.

[0060] In a period T₄, photoelectric conversion signals from the photoelectric conversion portions of the G₁ pixels (a₁₁, a₁₂, . . . , a_1n) are transferred to the capacitance C_TS1. Portions from the common amplifier to the capacitance C_TS1 are turned on by the pulses φ_L, φ_TS1, and φ_oS.

[0061] In accordance with a pulse φ_o11, the photoelectric conversion signals are transferred from the photoelectric conversion portions to the gate portion of the common amplifier. At this time point, the photoelectric conversion signals are added to the reset noise in the period T₂ at the gate. This gate voltage is superposed on the offset voltage of the common amplifier and stored in the capacitance C_TS1 as a signal (S₁+N₁).

[0062] After this, the vertical signal line is reset by the pulse φ_RV to remove residual charges on the signal line. In a period T₂′, the gate portions are reset. In a period T₃′, noise (N₂) of the common amplifiers is transferred. In a period T₄′, signals (S₂+N₂) from R₁ pixels are transferred. In a similar manner, in periods T₃″, and T₃′″, noise of the common amplifiers is transferred. In periods T₄″ and T₄′″, signals (S₃+N₃) from B₂ pixels and signals (S₄+N₄) from G₂ pixels (G pixel at the lower right in FIG. 5), to which noise is added, are transferred. A differential amplifier removes noise from the color signals, so signals S₁(G), S₂(R), S₃(B), and S₄(G) are output.

[0063] The interlaced scanning operation in odd fields have been described above. As described with reference to FIGS. 3A and 3B, the operation in even fields can be realized by changing the combinations of the vertical shift registers V_o and V_e.

[0064] A low pixel count read will be described next. Addition of G signals will be described.

[0065] When G signals from the photoelectric conversion portions a₁₁ and a₂₂ in a unit cell are to be added in an odd field, the signals can be add by the input portion of the common amplifier. However, when G signals from the photoelectric conversion portions a₂₂ and a₃₁ are to be added in an even field, the signals cannot be added by the input portion of the common amplifier. The G signals are read out from the unit cells and then added. In this case, signals added by the common amplifier and those output from the common amplifiers and then added must be switched by an interlace pulse. However, it is difficult to accurately match the gains.

[0066] In the present invention, both G signals from the photoelectric conversion portions a₁₁ and a₂₂ and G signals from the photoelectric conversion portions a₂₂ and a₃₁ are added by a horizontal transfer means. The color signal reading method is the same as that described with reference to FIG. 6.

[0067] Signals of the same color are added by the signal read circuit shown in FIG. 7. In the circuit shown in FIG. 7, addition processing is performed through the same signal system, and no gain difference is generated. Referring to FIG. 7, signals are simultaneously output from the capacitances C_TN1, C_TS1, C_TN2, C_TS2, C_TN3, C_TS3, C_TN4, and C_TS4 to the horizontal output line by a horizontal shift register (H·SR) serving as the horizontal transfer means and switching transistors connected to the horizontal shift register. After differential amplifiers A₁ to A₄ subtract noise from the signals (containing a noise component), the signals are added by an adder. As another method, signals from the capacitances C_TS1 and C_TS4 may be added, and signals from the capacitances C_TN1 and C_TN4 may be added by the horizontal output line. Alternatively, the temporary storage capacitances may be connected for addition.

[0068] FIG. 8 is a timing chart of an arrangement in which color separation is not performed using a single sensor. In this case, since signals have the same color, pixel signals can be added in the horizontal direction by the input portion of a common amplifier. In an odd field to be described below, signals a₁₁+a₁₂, a₂₁+a₂₂ . . . can be obtained.

[0069] In the period T₁, the vertical signal line is reset by the pulse φ_RV to remove residual charges on the signal line. Simultaneously, the residual charges on the temporary storage capacitances C_TN1, C_TN2, C_TS1, and C_TS2 are removed by pulses φ_TN1, φ_TN2, φ_TS1, and φ_TS2.

[0070] In the period T₂, the gate of the common amplifier is reset by the pulse φ_OR. In the period T₃, noise (N₁) of the common amplifier is transferred to a capacitance C_N1. In the period T₄, signals from a horizontal array of two photoelectric conversion portions are turned on by transfer pulses φ_on1 and φ_on2 and added by the gate portion. A signal (S₁+N₁; S₁ is the sum signal component of the horizontal array of two photoelectric conversion portions (a₁₁+a₁₂), and N₁ is the noise component) corresponding to the sum signal is transferred to a capacitance C_S1.

[0071] The vertical signal line is reset by the pulse φ_RV to remove residual charges on the signal line. In the period T₂′, the gate of the common amplifier is reset by the pulse φ_OR. In the period T₃′, the noise (N₂) of the common amplifier is transferred to a capacitance C_N2. In the period T₄′, signals from a horizontal array of two photoelectric conversion portions are turned on by transfer pulses φ_en1 and φ_en2 and added by the gate portion. A signal (S₂+N₂; S₂ is the sum signal component of the horizontal array of two photoelectric conversion portions (a₂₁+a₂₂), and N₂ is the noise component) corresponding to the sum signal is transferred to a capacitance C_S2.

[0072] As shown in FIGS. 3A and 3B, the operation in even fields can be realized by changing the combinations of the vertical shift registers V_o and V_e. In even fields, signals a₂₁+a₂₂, a₃₁+a₃₂, . . . can be obtained.

[0073] FIG. 9 is a circuit diagram of a read circuit for adding pixel signals in the vertical direction. The timing of reading out signals from the photoelectric conversion portions to the read circuit shown in FIG. 9 is the same as that described with reference to the timing chart shown in FIG. 6. Referring to FIG. 9, transistors for connecting the vertical output line to the capacitances C_TN1, C_TS1, C_TN2, C_TS2, C_TN3, C_TS3, C_TN4, and C_TS4 and the control signals φ_TN1, φ_TS1, φ_TN2, φ_TS2, φ_TN3, φ_TS3, φ_TN4, and φ_TS4 are not illustrated.

[0074] In the circuit shown in FIG. 9, signals are simultaneously output from the capacitances C_TN1, C_TS1, C_TN2, C_TS2, C_TN3, C_TS3, C_TN4, and C_TS4 to the horizontal output line by the horizontal shift register (H·SR) serving as a horizontal transfer means and switching transistors connected to the horizontal shift register. After the differential amplifiers A₁ to A₄ perform subtraction processing, signals S1 and S3 in the vertical direction are added by an adder. In odd fields, signals a₁₁+a₂₁, a₁₂+a₂₂, . . . are obtained. In the even fields, signals a₂₁+a₃₁, a₂₂+a₃₂ . . . are obtained. The signals may be added on the horizontal output line or temporary storage capacitances, as described above.

[0075] Addition of pixel signals in the horizontal direction or addition of pixel signals in the vertical or oblique direction is equivalent to the low pixel count signal read. For this reason, with driving according to the number of pixels in the recording or display system, a high-quality image with little moiré can be obtained at low power consumption.

[0076] In the above-described embodiment, signals from a plurality of photoelectric conversion portions are output to the vertical output line through common amplifiers. However, a circuit having functions except amplification may be used in place of the common amplifier to output the signals to the vertical output line.

[0077] That is to say, the image pickup apparatus of this embodiment includes a common circuit processing signals from a plurality of photoelectric conversion portions in common.

[0078] The second embodiment of the present invention will be described next.

[0079] In this embodiment, an addition switching means for arbitrarily switching addition of signals from a plurality of photoelectric conversion portions at the input portion of a common amplifier is used to allow switching between various addition reading and full pixel reading as shown in Table 1.

[0080] FIG. 11 a schematic view showing a sensor so as to explain a sensor signal read mode.

[0081] This sensor has 1,300,000 effective pixels (∝1024V×1280H), and four photoelectric conversion portions (e.g., a₁₁, a₁₂, a₂₁, and a₂₂) for one common amplifier. This sensor can switch the read mode between A. full pixel independent read mode, B. vertical/horizontal four-pixel addition read mode, C. horizontal two-pixel addition read mode, and D. vertical two-pixel addition read mode shown in Table 1. This embodiment is not limited to a sensor having four photoelectric conversion portions per common amplifier and can also be applied to a sensor having three or five or more photoelectric conversion portions per common amplifier.

[0082]

	TABLE 1
		Non-
	Read mode	Interlaced	Interlaced	Sensitivity
	A. Full Pixel	∘	Possible	×1
	Independent
	B. Vertical/	Possible	NTSC	×4
	Horizontal
	Four-Pixel
	Addition
	C. Horizontal	∘	Possible	×2
	Two-Pixel
	Addition
	D. Vertical	∘	Possible	×2
	Two-Pixel
	Addition

[0083] The full pixel read mode A in Table 1 is a read mode with priority on the resolution and used for, e.g., progressive (non-interlaced) 1,024 lines drive of a digital still camera. Signals are read sequentially in the order of line V₁ (a₁₁, a₁₂, . . . ), line V₂ (a₂₁, a₂₂, . . . ), . . . , line V₁₀₂₄ upon every horizontal scanning.

[0084] The sensitivity at this time is represented by 1 (the sensitivity is represented by only the ratio of the number of pixels to be added because the sensitivity changes depending on the frame frequency and the storage time in the interlaced mode or non-interlaced mode).

[0085] The vertical/horizontal four-pixel addition read mode B in Table 1 is preferably used for interlaced drive of NTSC. In odd fields, signals are read out in the order of lines V₁ and V₂, lines V₅ and V₆ . . . . In even fields, signals are read out in the order of lines V₃ and V₄, lines V₇ and V₈. Since four pixel signals are added, signals a₁₁+a₁₂+a₂₁+a₂₂, a₁₃+a₁₄+a₂₃+a₂₄, . . . are obtained from the lines V₁ and V₂.

[0086] The number of pixels after addition is 512V×640H. When 480V×640V signals are used, an NTSC signal is obtained. The sensitivity is four times (×8 in consideration of the interlaced mode) that of the full pixel read mode A.

[0087] In the horizontal two-pixel addition read mode C in Table 1, signals of two pixels adjacent in the horizontal direction are added. As a result, signals are read out in the order of line V₁ (a₁₁+a₁₂, a₁₃+a₁₄, . . . ), . . . , line V₁₀₂₄.

[0088] In the vertical two-pixel addition read mode D in Table 1, signals of two pixels adjacent in the vertical direction are added. As a result, signals are read out in the order of lines V₁ and V₂ (a₁₁+a₂₁, a₁₂+a₂₂, . . . , lines V₁₀₂₃ and V₁₀₂₄.

[0089] The read modes B, C, and D in Table 1 are used when the sensitivity need be increased in a low-illuminance environment, the number of pixels of the photographing monitor is small, or the capacity of the recording system need be reduced, or in a low power mode.

[0090] FIG. 10 is a schematic view showing the arrangement of an image pickup apparatus. The arrangement of a unit cell S of the image pickup apparatus shown in FIG. 10 is the same as that shown in FIG. 2.

[0091] As shown in FIG. 2, the unit cell S is formed by arranging four photoelectric conversion portions (a₁₁, a₁₂, a₂₁, and a₂₂) for one common amplifier. The remaining unit cells have the same arrangement as that of the unit cell. The common amplifier comprises an amplification means MSF, reset means MRES, and select means MSEL. The input portion of the common amplifier corresponds to the gate portion of the amplification means MSF.

[0092] Lines for controlling signal transfer for two upper photoelectric conversion portions (a₁₁ and a₁₂) of the four pixels, that are adjacent to each other in the horizontal direction are connected to an odd vertical shift register V_o (V_o1, V_o2, V_o3, . . . ). Lines for controlling signal transfer for two lower photoelectric conversion portions (a₂₁ and a₂₂) that are adjacent to each other in the horizontal direction are connected to an even-numbered vertical shift register V_e (V_e1, V_e2, V_e3, . . . ). The reset switch MRES and select switch MSEL of the common amplifier are connected to the corresponding vertical shift registers V_o and V_e through an odd selection circuit S_o and an even selection circuit S_e, respectively. The vertical shift registers V_o and V_e and selection circuits S_o and S_e can be independently controlled. The vertical shift registers V_o and V_e and selection circuits S_o and S_e construct an addition switching means.

[0093] FIGS. 12A and 12B show driving examples of the vertical shift registers corresponding to the read modes shown in Table 1. FIG. 12A shows non-interlaced (progressive) driving. Control signals φ_o (φ_o11, φ_o12, φ_o21, φ_o22, . . . ) are output from the vertical shift registers V_o while control signals φ_e (φ_e11, φ_e12, φ_e21, φ_e22, . . . ) are output from the vertical shift registers V_e. Scanning is sequentially performed every 1H interval, and the pixel signals of the horizontal lines are sequentially controlled. This driving allows the full pixel independent read or horizontal two-pixel addition read.

[0094] FIG. 12B shows two-line simultaneous driving in units of four pixels of a common amplifier or two vertically adjoining pixels. The control signals φ_o from the vertical shift registers V_o and the control signals φ_e from the vertical shift registers V_e are driven in phase. This driving allows the vertical two-pixel addition read or vertical/horizontal four-pixel addition read.

[0095] The read modes shown in Table 1 will be described in more detail with reference to timing charts.

[0096] FIG. 13 is a timing chart of the read mode A (full pixel read).

[0097] In a horizontal blanking period (HBLK), signals photoelectrically converted in the pixels are transferred, and the photoelectric conversion portions are reset to the initial state. Signal transfer and reset of the photoelectric conversion portions of the first row are controlled by the odd vertical shift register V_o and odd selection circuit S_o.

[0098] In a period T₁, the vertical signal line is reset by a pulse φ_RV to remove residual charges on the signal line. In addition, the residual charges on temporary storage capacitances C_TN1, C_TN2, C_TS1, and C_TS2 by pulses φ_TN1, φ_TN2, φ_TS1, and φ_TS2, respectively.

[0099] In a period T₂, as preprocessing for transfer of odd-numbered photoelectric conversion signals in the photoelectric conversion portions (a₁₁, a₁₂, . . . , a_1n) of the first row, the gate portion of the amplification means MSF of each common amplifier is reset by a pulse φ_oR to remove residual charges. After removal, reset noise remains in the gate portion.

[0100] In a period T₃, the reset noise and the offset voltage of the common amplifier in the period T₂ are transferred to the capacitance C_TN1. The output portion of each common amplifier is connected to the vertical signal line in accordance with a pulse φ_oS, a load MOS transistor is turned on in accordance with a pulse φ_L to operate the common amplifier, and the vertical signal line and capacitance C_TN1 are connected in accordance with the pulse φ_TN1. Noise (N) is stored in the capacitance C_TN1.

[0101] In a period T₄, odd-numbered (a₁₁, a₁₃, . . . , a_1n) photoelectric conversion signals are transferred to the capacitance C_TS1. Portions from the common amplifier to the capacitance C_TS1 are turned on by the pulses φ_L, φ_TS1, and φ_oS.

[0102] In accordance with a pulse φ_o11, the photoelectric conversion signals are transferred from the photoelectric conversion portions to the gate portion of the common amplifier. At this time point, the photoelectric conversion portions are added to the reset noise in the period T₂ at the gate. This gate voltage is superposed on the offset voltage of the common amplifier and stored in the capacitance C_TS1 as a signal (S+N).

[0103] In periods T₅ to T₈, even-numbered photoelectric conversion signals (a₁₂, a₁₄, . . . , a_1n−1) are transferred to the capacitance C_TS2. The basic operation is the same as in the periods T₁ to T₄ except that pulse control changes as φ_o11→φ_o12, φ_TN1→φ_TN2, and φ_TS1→φ_TS2.

[0104] In a period T₉, residual charges between the vertical signal line, common amplifier, and transfer MOS transistor are removed, thereby ending the basic operation of transferring the reset noise and photoelectric conversion signals.

[0105] With the above-described driving, the noise components N1 and N2 and signals S1+N1 and S2+N2 are stored in the capacitances. These noise and signal components are transferred to the horizontal output line in accordance with pulses φH1 and φH2 from the horizontal shift register during a period T₁₀. An output amplifier A1 calculates subtraction (S1+N1)−N1 to output the signal S1. An output amplifier A2 calculates subtraction (S2+N2)−N2 to output the signal S2.

[0106] With this operation, only the photoelectric conversion signals of the row (a₁₁, . . . , a_1n) to undergo photoelectric conversion are obtained. To store pixel signals of the row, when the photoelectric conversion signals are transferred to the gate portion in the periods T₄ and T₈, photoelectric conversion is started.

[0107] In the next horizontal blanking period, signals from the photoelectric conversion portions of the second row are read as in the first row. Signal transfer and reset of the photoelectric conversion portions of the second row are controlled by the even vertical shift register V_e and even selection circuit S_e.

[0108] FIG. 14 is a timing chart schematically showing the vertical timing. In a vertical period, the above-described operation in the horizontal period is sequentially performed a number of times equal to the number of pixels in the vertical direction. The vertical shift registers output driving pulses φ_on1, φ_on2 (φ_en1, φ_en2), φ_oRn, φ_oSn, (φ_eRn, φ_eSn) in units of rows every 1H interval.

[0109] FIG. 15 is a timing chart of the read mode B (vertical/horizontal four-pixel addition). Signal transfer and reset of vertical/horizontal four-pixel sum signals are controlled by odd and even vertical shift registers V_o and V_e and odd selection circuits S_o (or even selection circuits S_e).

[0110] In the period T₁, the vertical signal line is reset by the pulse φ_RV to remove residual charges on the signal line. In addition, the residual charges on the temporary storage capacitances C_TN1 and C_TS1 are removed by the pulses φ_TN1 and φ_TS1.

[0111] In the period T₂, the gate of the common amplifier is reset by the pulse φ_OR. In the period T₃, noise (V_n) of the common amplifier is transferred to the capacitance C_TN1. In the period T₄, transfer switches MTX1 to MTX4 of four pixels are turned on by the transfer pulses φ_o11, φ_o12, φ_e11, and φ_e12, and signals from the photoelectric conversion portions are added by the gate portion of the amplification means MSF of the common amplifier. A signal (V_s+V_n; V_s is the sum signal component of four photoelectric conversion portions (a₁₁+a₁₂+a₂₁+a₂₂), and V_n is the noise component) corresponding to the sum signal is transferred to the capacitance C_TS1. The differential amplifier A1 removes the noise (V_n) from the signal and noise components. The output signal S1 contains only the photoelectric conversion signal (V_s) without amplifier noise. In the interlaced driving mode, driving is performed every other line.

[0112] In the next horizontal blanking period, the operation of the photoelectric conversion portions of the third and fourth rows is performed as in the first and second rows.

[0113] FIG. 16 is a timing chart of the read mode C (horizontal two-pixel addition). Signal transfer and reset of the photoelectric conversion portions of the first row are controlled by the odd vertical shift register V_o and odd selection circuit S_o.

[0114] In the period T₁, the vertical signal line is reset by the pulse φ_RV to remove residual charges on the signal line. In addition, the residual charges on the temporary storage capacitances C_TN1 and C_TS1 are removed by the pulses φ_TN1 and φ_TS1.

[0115] In the period T₂, the gate of the amplification means MSF of the common amplifier is reset by the pulse φ_OR. In the period T₃, the noise (V_n) of the common amplifier is transferred to a capacitance C_N1. In the period T₄, signals from a horizontal array of two photoelectric conversion portions are turned on by the transfer pulses φ_on1 and φ_on2 and added by the gate portion. A signal (V_s+V_n; V_s is the sum signal component of the horizontal array of two photoelectric conversion portions (a₁₁+a₁₂), and V_n is the noise component) corresponding to the sum signal is transferred to a capacitance C_S1. The differential amplifier A1 removes the noise (V_n) from the signal and noise components. The output signal S1 contains only the photoelectric conversion signal (V_s) without amplifier noise.

[0116] In the next horizontal blanking period, the operation of the photoelectric conversion portions of the second row is performed as in the first row.

Signal transfer and reset of the photoelectric conversion portions of the second row are controlled by the even vertical shift register V_e and even selection circuit S_e.

[0117] FIG. 17 is a timing chart of the read mode D (vertical two-pixel addition). Signal transfer and reset of vertical two-pixel sum signals are controlled by odd and even vertical shift registers V_o and V_e and odd selection circuits S_o (or even selection circuits S_e).

[0118] In the period T₁, the vertical signal line is reset by the pulse φ_RV to remove residual charges on the signal line. In addition, the residual charges on the temporary storage capacitances C_TN1, C_TN2, C_TS1, and C_TS2 are removed by the pulses φ_TN1, φ_TN2, φ_TS1, and φ_TS2, respectively.

[0119] In the period T₂, the gate of the amplification means MSF of the common amplifier is reset by a pulse φ_OR1. In the period T₃, noise (V_n1) of the common amplifier is transferred to the capacitance C_N1. In the period T₄, signals from a vertical array of two photoelectric conversion portions of the first column are turned on by transfer pulses φ_on1 and φ_en1 and added by the gate portion. A signal (V_s1+V_n1; V_s1 is the sum signal component of the vertical array of two photoelectric conversion portions (a₁₁+a₂₁), and V_n1 is the noise component) corresponding to the sum signal is transferred to the capacitance C_S1.

[0120] In the period T₅, the gate of the amplification means MSF of the common amplifier is reset by the pulse φ_OR1. In the period T₆, noise (V_n2) of the common amplifier is transferred to the capacitance C_N2. In the period T₇, signals from a vertical array of two photoelectric conversion portions of the second column are turned on by transfer pulses φ_on2 and φ_en2 and added by the gate portion. A signal (V_s2+V_n2; V_s2 is the sum signal component of the vertical array of two photoelectric conversion portions (a₁₂+a₂₂), and V_n2 is the noise component) corresponding to the sum signal is transferred to the capacitance C_S2. After this, noise of a capacitance C_n1 is removed from the signal of the capacitance C_S1, and noise of a capacitance C_n2 is removed from the signal of the capacitance C_S2.

[0121] In the next horizontal blanking period, the operation of the photoelectric conversion portions of the third and fourth rows is performed as in the first and second rows.

[0122] In the above arrangement, signals from a plurality of photoelectric conversion portions are output to the vertical output line through common amplifiers. However, a circuit having functions except amplification may be used in place of the common amplifier to output the signals to the vertical output line.

[0123] That is to say, the image pickup apparatus of this embodiment includes a common circuit processing signals from a plurality of photoelectric conversion portions in common.

[0124] The third embodiment of the present invention will be described next.

[0125] In first embodiment signals from a plurality of photoelectric conversion portions in a unit cell and outside the unit cell can be added. In second embodiment, the mode can be switched between a mode for independently reading out signals from all photoelectric conversion portions of the unit cell, a mode for reading out a sum signal from four photoelectric conversion portions of the unit cell in the vertical and horizontal directions, a mode for reading out a sum signal from two, horizontally adjacent photoelectric conversion portions of the unit cell, and a mode for reading out a sum signal from two, vertically adjacent photoelectric conversion portions of the unit cell.

[0126] In this embodiment, the above four modes can be switched by combining the arrangements of the first and second embodiments. In addition, not only a sum signal from a plurality of photoelectric conversion portions in the unit cell but also a sum signal from a plurality of photoelectric conversion portions in different unit cells can be obtained.

[0127] FIG. 18 is a block diagram showing the schematic arrangement of an image pickup system according to the fourth embodiment of the present invention, in which the image pickup apparatus described in the first to third embodiments is used. As shown in FIG. 18, the image of light incident through an optical system 71 and stop 80 is formed on an image pickup apparatus 72. The optical information is converted into an electrical signal by a pixel array formed on the image pickup apparatus 72. A signal processing circuit 73 processes the electrical signal by a predetermined method and outputs the signal. The processed signal is recorded or transferred by a recording system/communication system 74. The recorded or transferred signal is reproduced by a reproduction system 77. The iris 80, image pickup apparatus 72, and signal processing circuit 73 are controlled by a timing control circuit 75. The optical system 71, timing control circuit 75, recording system/communication system 74, and reproduction system 77 are controlled by a system control circuit 76. The image pickup apparatus 72 and the remaining signal processing circuits may be formed on different semiconductor substrates or on a single semiconductor substrate by the CMOS process.

[0128] The above-described high pixel count read (full pixel read) and low pixel count read (addition read) use different horizontal and vertical driving pulses. Hence, the sensor drive timing, resolution processing by the signal processing circuit, and the number of pixels to be recorded by the recording system must be changed in units of read modes. This change is controlled by the system control circuit 76 according to each read mode. In the read mode, the sensitivity is changed by addition. For example, the signal amount in the addition read is twice that in the high pixel count read, and the dynamic range is halved. In this case, an appropriate signal is obtained by controlling the iris 80 to be smaller by ½. This allows photographing at a ½ illuminance.

[0129] In fifth embodiment, the detailed arrangement of the unit cell suitable for the image pickup apparatus described in the first to third embodiments will be described.

[0130] The layout shown in FIG. 26 has the following problem because photoelectric conversion portions 173 are not laid out at an equal interval (a₁≠a₂), and the areas (light-receiving portions) for sensing light in the pixels are not arranged at an equal interval. More specifically, a layout with different pitches partially have different spatial frequencies and resolutions and therefore reduces the resolution or generate errors such as moiré fringes. Moiré fringes pose a very serious problem, and an image pickup apparatus having moiré fringes is practically useless as a product. This also applies when the number of pixels of the unit cell is not 4.

[0131] The present inventors have proposed that even in an image pickup apparatus having an amplification means distributed to a plurality of pixels, when the photoelectric conversion portions are laid out at an equal pitch, the light-receiving portions can be laid out at an equal pitch, any decrease in resolution and moiré fringes can be prevented, the opening ratio can be increased, and satisfactory performance can be obtained.

[0132] FIG. 19 is a view showing an example in which 2×2 pixels share a common amplifier portion 12. Referring to FIG. 19, the common amplifier portion 12 to be shared is arranged at the center of the four pixels, and four photoelectric conversion portions (a₁₁, a₁₂, a₂₁, and a₂₂) surround the common amplifier portion 12. The common amplifier portion 12 includes not only an amplification means MSF, reset means MRES, and select means MSEL shown in FIG. 2 but also transfer means MTX1 to MTX4.

[0133] A light-shielding portion 15 is present at a position line-symmetric with respect to the area of the common amplifier portion 12 in each pixel. Hence, the center of gravity of a photoelectric conversion portion 11 of each pixel is present at the center of the pixel. The four photoelectric conversion portions (a₁₁ to a₂₂) can be laid out at an equal interval a in the vertical and horizontal directions.

[0134] Referring to FIG. 20, a common amplifier portion 22 to be shared is arranged at the central portion of four pixels in the horizontal direction, and four photoelectric conversion portions (a₁₁, a₁₂, a₂₁, and a₂₂) 21 sandwich the common amplifier portion 22.

[0135] A light-shielding portion 25 is present at a position line-symmetric with respect to the area of the common amplifier portion 22 in each pixel. Hence, the center of gravity of the photoelectric conversion portion 21 of each pixel is present at the center of the pixel. The four photoelectric conversion portions (a₁₁ to a₂₂) can be laid out at the equal interval a in the vertical and horizontal directions.

[0136] In the embodiment shown in FIG. 20, the horizontal and vertical directions may be replaced.

[0137] FIG. 21 is a view showing the detailed pattern layout of the first example of the pixel array portion of the image pickup apparatus.

[0138] The image pickup apparatus shown in FIG. 21 is formed on a single-crystal substrate by a layout rule of 0.4 μm. The pixel is an 8-μm side square. The source follower amplifier as an amplification means is shared by 2×2=4 pixels. Hence, each of repeated unit cells 81 is a 16 μm×16 μm side square, and a two-dimensional array is formed.

[0139] Photodiodes 82a, 82b, 82c, and 82d as photoelectric conversion portions are formed diagonally at the centers of the pixels. The photodiodes have an almost rotationally symmetric and mirror-image symmetric shape in the vertical and horizontal directions. The photodiodes 82a, 82b, 82c, and 82d have the same center g of gravity in the pixels. Light-shielding portions 95 are also formed.

[0140] The image pickup apparatus also has a scanning line 88a for controlling a transfer gate 83a at the upper left, a row selection line 90, and a reset line 92 for controlling a MOS gate 93.

[0141] Signal charges stored in the photodiodes 82a to 82d are sent to an FD 85 through transfer gates 83a to 83d. The MOS size of each of the gates 83a to 83d is L=0.4 μm and W=1.0 μm (L is the channel length, and W is the channel width).

[0142] The FD 85 is connected to an input gate 86 of the source follower through a 0.4 μm-wide A1 interconnection. The signal charges transferred to the FD 85 modulate the voltage of the input gate 86. The MOS size of the input gate 86 is L=0 8 μm and W=1.0 μm. The sum of capacitances of the FD 85 and input gate 86 is about 5 fF. Since Q=CV, the voltage of the input gate 86 changes by 3.2 V by storing 10⁵ electrons.

[0143] A current flowing from a V_DD terminal 91 is modulated by the input gate 86 and flowed to a vertical signal line 87. The current flowed to the vertical signal line 87 is processed by a signal processing circuit (not shown) and finally output as image information.

[0144] After this, to set the potential of the photodiodes 82a to 82d, FD 85, and input gate 86 to a predetermined value V_DD, the MOS gate 93 connected to the reset line 92 is opened (the transfer gates 83a to 83d are also opened), thereby short-circuiting the photodiodes 82a to 82d, FD 85, and input gate 86 to the V_DD terminal.

[0145] After this, the transfer gates 83a to 83d are closed to restart charge storage by the photodiodes 82a to 82d.

[0146] Note that since interconnections 88a to 88d, 90, and 92 extending in the horizontal direction are formed from ITO (Indium Tin Oxide) with a thickness of 1,500 Å as a transparent conductor, light passes through the interconnection portions on the photodiodes 82a to 82d, and the center g of gravity of each photodiode matches the center of gravity of the area (light-receiving portion) for sensing light.

[0147] According to this example, a MOS sensor having an equal pitch and a relatively high area ratio and opening ratio can be provided.

[0148] FIG. 22 is a view showing the detailed pattern layout of the second example of the pixel array portion of the image pickup apparatus.

[0149] Referring to FIG. 22, the image pickup apparatus has photodiodes 102a to 102d, transfer gates 103a to 103d, a FD 105, an input gate 106 of a source follower, a vertical signal line 107, scanning lines 108a to 108d, a row selection line 110, and a reset line 112 for controlling a MOS gate 113.

[0150] In this example, three of the interconnections 108a to 108d, 110 and 112 run across the centers of the pixels in the horizontal direction. For this reason, even when the metal interconnections intercept light incident on the photodiodes 102a to 102d, the center g of gravity of the area for sensing light does not move and matches the center of each pixel.

[0151] According to this example, since an ordinary (opaque) metal with a small electrical resistance can be used, the time constants of interconnections in the horizontal direction improve, so a higher-speed image pickup apparatus can be provided.

[0152] In the above example, since the portion under the light-shielding film is effectively used, a photodiode serving as a photoelectric conversion portion may be formed even under the light-shielding film and functioned as a charge storage portion, as shown in FIG. 23.

[0153] In the second example, since the interconnections run across the center of each pixel with the highest light collection efficiency, the sensitivity of the image pickup apparatus may decrease. FIG. 24 shows a further improved third example.

[0154] In this example, since all of transfer gates 123a to 123d, an FD 125, an input gate 126 of a source follower, and a reset MOS gate 133 are formed under interconnections (scanning lines 128a to 128d, a row selection line 130, and a rest line 132) running in the horizontal direction, photodiodes 122a to 122d and their opening portions can be maximized. In addition, the opening portions are continuously present at the centers of the pixels. Light-shielding portions are formed in the horizontal and vertical interconnection portions.

[0155] In this example, since the source follower serving as the amplification means and the reset MOS transistor are divided in the horizontal direction around the pixels, they can be compactly layed out under the horizontal interconnections.

[0156] Furthermore, since an unused space still exists under the interconnections of the upper right pixel, a new component such as a smart sensor can be added.

[0157] According to this example, since the area and opening ratio of each photodiode can be made large, an image pickup apparatus with a wide dynamic range and high sensitivity can be provided. Even when the pixel size further shrinks, and the size of the opening portion of each photodiode becomes as small as the wavelength of light, light incidence is unlikely to be impeded, and the performance can be exhibited for a long time.

[0158] In the above example, the amplification means is arranged at the central portion of the unit cell, and the center of gravity of the area for sensing light matches the center of the pixel. However, the present invention is not limited to this, and an arrangement in which the opening portions have a translationally symmetric shape may be used, as shown in FIG. 25.

[0159] That is, when the opening portions are translationally symmetric, the areas for sensing light are laid out at an equal pitch.

[0160] As has been described above, according to the first to fifth embodiments, a high opening ratio can be obtained by forming a plurality of photoelectric conversion portions per common amplifier. In addition, a high-quality image can be obtained even by interlaced driving. In low pixel count driving, a high-quality image with little moiré can be obtained at low power consumption as a pixel image to be recorded or displayed. Furthermore, the sensitivity increases to allow low-illuminance photographing.

[0161] Many widely different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.