JP2016092791A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device suppressing deterioration of image quality, by making the degree of whitening, occurring by light emission of a column circuit, uniform near the center of upper and lower ends and at the left and right ends of the screen.SOLUTION: An imaging device includes a pixel array where unit pixels including a plurality of photoelectric conversion elements are arranged in matrix, and a plurality of column circuits being driven in relation to an operation for reading the imaging signal of the pixel array for each column thereof. The pixel array and a plurality of column circuits are arranged so that the overall breadth of the plurality of column circuits is wider than the breadth of the pixel array.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image sensor having a column circuit, and more particularly to an arrangement of the column circuit of the image sensor.

  A CMOS (Complementary Metal-Oxide Semiconductor) image pickup device is known as an image pickup device used for an image pickup apparatus such as a digital still camera or a digital video camera. This CMOS image sensor is provided with a column circuit for reading an image pickup signal from pixels two-dimensionally arranged in the row direction and the column direction. As an example of the influence on imaging by the column circuit, when the column circuit is driven, the column circuit may emit light even though it is minute. In the photoelectric conversion element of the pixel arranged near the column circuit, the column circuit It can be mentioned that the signal level of the imaging signal changes by reacting to the emitted light, and whitening occurs in the obtained image.

  In response to this phenomenon, Patent Document 1 discloses a technique of alternately reading out image signals from pixels at least one row from the upper and lower ends toward the center in order to suppress whitening of the screen due to light emission of the column circuit. Yes. As a result, it is possible to suppress whitening of the screen edge due to the light emission of the column circuit.

JP 2013-121027 A

  However, in the imaging signal readout method disclosed in Patent Document 1, when a two-dimensional image is generated using imaging signals read from all rows, the rows need to be rearranged, and the burden of the rearrangement processing is generated. To do.

  If image signals are sequentially read out from pixels in order to eliminate the rearrangement process, the degree of whitening caused by light emission from the column circuit differs between the vicinity of the center of the upper and lower ends of the screen and the left and right ends. Near the center of the upper and lower edges of the screen, it is affected by light emission from the surrounding column circuits, but at the left and right edges of the upper and lower edges of the screen, there is no column circuit arranged on either the left or right side. The degree is smaller than near the center. Therefore, white floating occurs at different levels near the center of the upper and lower ends of the screen and on the left and right ends.

  When the degree of whitening is different, two-dimensional shading occurs in the screen, which degrades the image quality. For this reason, it is necessary to correct the two-dimensional shading, and the correction process cannot be easily performed. On the other hand, when the degree of whitening is made uniform, one-dimensional shading occurs in the screen. The process of correcting the one-dimensional shading can be performed more easily than the process of correcting the two-dimensional shading.

  Accordingly, an object of the present invention is to reduce the image quality by making the degree of whitening caused by the light emission of the column circuit uniform in the vicinity of the center of the upper and lower ends of the screen and the left and right ends when reading out the imaging signals sequentially from the pixels. The object is to provide a suppressed image sensor.

  In order to achieve the above object, an imaging device of the present invention includes a pixel array unit in which unit pixels each having a plurality of photoelectric conversion elements are arranged in a matrix, and imaging of the pixel array unit for each column of the pixel array unit. A plurality of column circuits driven in association with an operation of reading signals, and the horizontal width of the entire plurality of column circuits is wider than the horizontal width of the pixel array unit. A circuit is arranged.

  According to the present invention, in an imaging device including a column circuit, the degree of whitening caused by light emission of the column circuit is made uniform near the center of the upper and lower ends of the screen and the left and right ends, thereby suppressing image quality deterioration. Can be provided.

It is a block diagram which shows the structural example of the image pick-up element concerning 1st Embodiment. 1 is a simplified circuit diagram of an image sensor according to an embodiment of the present invention. It is a timing chart which shows an example drive timing in one horizontal period in the case of reading an image pick-up signal from a pixel part concerning an embodiment of the present invention. It is a timing chart which shows an example drive timing in the case of reading an imaging signal in all pixel reset concerning an embodiment of the present invention. It is a block diagram which shows the structural example of the image pick-up element concerning 2nd Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Each embodiment will be described with the column circuit light source as a column amplifier described later.

<First Embodiment>
FIG. 1 is a block diagram showing an example of an image sensor according to an embodiment of the present invention. An image sensor 100 according to the present invention includes a pixel array unit 102 composed of a plurality of pixel units 101, a vertical output line 103, a load current source 105 and a readout circuit 106 as a column circuit 104, column selection switches 107 and 108, vertical scanning. A circuit 109, a horizontal scanning circuit 110, horizontal output lines 111 and 112, an output amplifier 113, and reset switches 114 and 115 are included.

  FIG. 1 shows a configuration including a noise removal circuit. As will be described in detail later, an imaging signal is output to the horizontal output line 112, and a noise signal is output to the horizontal output line 111. The output amplifier 113 subtracts the noise signal input from the horizontal output line 111 from the image pickup signal input from the horizontal output line 112 and outputs the result to the outside of the image sensor 100. Here, the imaging signal is a signal including an optical signal and a noise signal. In the pixel array unit 102, a plurality of pixel units 101 including photoelectric conversion elements are two-dimensionally arranged in the row direction and the column direction. The vertical output line 103 is a signal line that outputs an imaging signal from the pixel 101 for each column.

  The load current source 105 is driven via the vertical output line 103 in order to read out the imaging signal from the pixel 101. The readout circuit 106 is commonly connected to the plurality of pixels 101 in the corresponding column via the vertical output line 103, and amplifies and records the imaging signal from the pixel 101. The column selection switches 107 and 108 control connection between the output terminal of the column circuit 104 and the horizontal output lines 111 and 112. The vertical scanning circuit 109 supplies signals φTXn, φRESn and signal φSELn to the pixels 101 in each row, and controls reading of signal charges. The horizontal scanning circuit 110 sequentially outputs signals from the readout circuit 106 to the horizontal output lines 111 and 112.

  The output amplifier 113 outputs the signals of the horizontal output lines 111 and 112 to the outside of the image sensor 100. The reset switches 114 and 115 are ON / OFF controlled by the signal φCHR, and the horizontal output lines 111 and 112 are reset by the reset power source VCHR for each horizontal scanning signal (one signal φH).

  FIG. 2 is a simplified circuit diagram of the image sensor 100. The pixel unit 101 includes a photodiode 200, a transfer switch 201, a reset switch 202, a storage capacitor 203, a source follower 204, and a row selection switch 205. The photodiode 200 as a photoelectric conversion element generates and accumulates signal charges corresponding to the irradiated light.

  The transfer switch 201 is controlled to be turned ON / OFF by a signal φTXn, and transfers the signal charge generated and stored in the photodiode 200 to the storage capacitor 203. The storage capacitor 203 stores the signal charge transferred by the transfer switch 201. The reset switch 202 is controlled to be turned on / off by a signal φRESn, and resets unnecessary signal charges accumulated in the photodiode 200 and the storage capacitor 203.

  The source follower 204 amplifies the signal charge stored in the storage capacitor 203 and converts it into a voltage. The reset switch 202, the storage capacitor 203, and the source follower 204 constitute a floating diffusion amplifier. The row selection switch 205 is ON / OFF controlled by a signal φSELn, and controls the connection between the output of the source follower 204 and the vertical output line 103. The read circuit 106 includes a clamp capacitor 206, a feedback capacitor 207, a clamp switch 208, a column amplifier 209, transfer switches 210 and 211, and transfer capacitors 212 and 213. The clamp capacitor 206 clamps a signal from the vertical output line 103.

  The inverting input terminal of the column amplifier 209 is connected to the output terminal of the column amplifier 209 via the feedback capacitor 207. The column amplifier 209 amplifies the output of the clamp capacitor 206. The amplification factor of the column amplifier 209 is determined by the ratio between the clamp capacitor 206 and the feedback capacitor 207. The power supply Vref is input to the non-inverting input terminal of the column amplifier 209. The clamp switch 208 is ON / OFF controlled by a signal φCLAMP and is disposed between the inverting input terminal and the output terminal of the column amplifier 209.

  The signal amplified by the column amplifier 209 is stored in the transfer capacitors 212 and 213 via the transfer switches 210 and 211. The signals stored in the transfer capacitors 212 and 213 are output to the horizontal output lines 111 and 112 by turning on the column selection switches 107 and 108 that are controlled to be turned on / off according to the signal φH from the horizontal scanning circuit 110. Is done. The output amplifier 113 outputs a difference signal (hereinafter referred to as an image signal) between an imaging signal input from one of the horizontal output lines 111 and 112 and a noise signal input from the other of the horizontal output lines 112 and 111. Output to the outside of the image sensor 100.

  By the way, when reading the imaging signal, there is a possibility that the column amplifier 209 drives the column amplifier 209 to emit light while being minute. Thereby, at least the pixel portion 101 arranged near the readout circuit 106 may change the signal level of the imaging signal in response to the light emitted from the column circuit 104.

  The degree of the influence of the light emission of the column amplifier 209 differs between the vicinity of the center at the upper and lower ends of the screen and the left and right ends. Near the center of the upper and lower ends of the screen, it is affected by light emission by the surrounding column amplifiers 209. However, at the left and right ends of the upper and lower ends of the screen, the column circuit 104 is not arranged on either the left or right side. The effect is smaller than near the center. Therefore, white floating occurs at different levels near the center of the upper and lower ends of the screen and on the left and right ends.

  Therefore, in this embodiment, as shown in FIG. 1, the column circuit 104 is arranged so that the entire horizontal width of the column circuit 104 is larger than the horizontal width of the pixel array unit 102. Here, the column circuit 104 is arranged so that the distance from the pixel unit 101 of each column arranged at the upper and lower ends of the pixel array unit 102 to the column amplifier 209 which is a light emission source arranged at the upper and lower ends is constant. To do. Therefore, by arranging the column circuit 104 at the position described above, it is possible to make the degree of whitening caused by the light emission of the column circuit 104 uniform between the center of the upper and lower ends of the screen and the left and right ends.

  FIG. 3 is a timing chart showing an example of driving timing for one horizontal period when an imaging signal is read from the pixel unit 101. Each signal in the figure is assumed to be in a high (hereinafter referred to as “H”) or low (hereinafter referred to as “L”) state.

  Hereinafter, a reading operation for the pixel unit 101 arranged in the n-th row in the plurality of imaging elements 100 arranged two-dimensionally will be described. For convenience of explanation, the “signal φSEL in the nth row” is referred to as “signal φSELn”. The same applies to the signals φRES and φTX. In addition, “the pixel portion 101 in the n-th row” is appropriately referred to as “pixel portion 101”. At time t <b> 1, the signal φSELn becomes “H”, the row selection switch 205 is turned on, and the circuit of the pixel portion 101 is connected to the vertical output line 103. At the same time, the signal φRESn becomes “H”, the reset switch 202 is turned ON, and unnecessary charges stored in the storage capacitor 203 are reset.

  At time t2, the signal φRESn becomes “L”, the reset switch 202 is turned OFF, and the resetting of unnecessary charges is completed. At the same time, the signal φCLAMP is set to “H” and the clamp switch 208 is turned ON. As a result, the noise signal generated in the pixel 101 is clamped by the clamp capacitor 206 connected via the vertical output line 103. At time t3, the signal φCLAMP becomes “L” and the clamp switch 208 is turned OFF. Thereby, the clamping of the noise signal generated in the pixel unit 101 to the clamp capacitor 206 connected by the vertical output line 103 is completed. At the same time, the signal φTN becomes “H”, the transfer switch 210 is turned on, and the noise signal is transferred to the transfer capacitor 212.

  At time t4, the signal φTN becomes “L”, the transfer switch 210 is turned off, and the transfer of the noise signal in the transfer capacitor 212 is completed. At time t5, the signal φTXn becomes “H” and the transfer switch 201 is turned on. As a result, the signal charge stored in the photodiode 200 is transferred to the storage capacitor 203. The signal charge transferred to the storage capacitor 203 is amplified by the source follower 204, and the signal charge is converted into a voltage and output to the vertical output line 103.

  At time t6, the signal φTXn becomes “L”, the transfer switch 201 is turned off, and the transfer of the signal charge to the storage capacitor 203 is completed. At the same time, the signal φTS becomes “H” and the transfer switch 211 is turned ON. The imaging signal output to the vertical output line 103 is transferred to the transfer capacitor 213 via the clamp capacitor 206 and the column amplifier 209.

  At time t7, the signal φTS becomes “L”, the transfer switch 211 is turned OFF, and the transfer of the imaging signal in the transfer capacitor 213 is finished. At time t8, the signal φSELn becomes “L”, the row selection switch 205 is turned OFF, and the readout of the imaging signal from the pixel unit 101 is completed. At time t <b> 9, the signal φHST becomes “L”, and a horizontal scanning period starts for the signal of the pixel portion 101. Input of the signal φH to the horizontal scanning circuit 110 is started. The horizontal scanning circuit 110 sequentially turns on the column selection switches 107 and 108 in response to the signal φH.

  When the column selection switches 107 and 108 are turned ON, the signals stored in the transfer capacitors 212 and 213 are output to the horizontal output lines 111 and 112, respectively. Then, the output amplifier 113 subtracts the noise signal input to the horizontal output line 111 from the image pickup signal input via the horizontal output line 112 and outputs it as an image signal for one row.

  When reading an imaging signal, it is necessary to drive the column circuit at least during a period from time t2 to t9. At this time, driving the column amplifier 209 may cause the column amplifier 209 to emit light while being minute. Therefore, at least the photodiode 200 of the pixel portion 101 disposed near the column amplifier 209 may change the signal level of the imaging signal in response to light emitted from the column circuit.

  As described above, the degree of influence by light emission of the column amplifier 209 differs between the vicinity of the center at the upper and lower ends of the screen and the left and right ends. For this reason, the degree of whitening that occurs near the center at the upper and lower ends of the screen differs from that at the left and right ends. Therefore, in this embodiment, the pixel array unit 102 and the column circuit 104 are arranged so that the entire horizontal width of the column circuit 104 is larger than the horizontal width of the pixel array unit 102 as shown in FIG. The degree of whitening caused by the light emission of the circuit 104 can be made uniform near the center of the upper and lower ends of the screen and at the left and right ends.

<Second Embodiment>
Hereinafter, a second embodiment of the present invention will be described. When the imaging device of the present invention is used in an imaging device such as a digital camera, in order to adjust the exposure time of all the pixels, after resetting the signal charges of all the pixels at the same time before storing the signal charges, A driving method is conceivable in which the exposure time is made uniform with a mechanical shutter and the imaging signal is read out sequentially for each row. Such drive timing will be described with reference to FIG.

  FIG. 4 is a timing chart showing an example of driving timing when an image pickup signal is read in all pixel reset. At time t <b> 10, the signal φRES becomes “H”, the reset switch 202 is turned ON, and resetting of unnecessary charges accumulated in the storage capacitor 203 is started. At time t11, the signal φRES becomes “L”, the reset switch 202 is turned OFF, and the resetting of unnecessary charges is completed. At the same time, accumulation of signal charges is started in the photodiode 200.

  At time t12, the accumulation of signal charges in the photodiode 200 ends. The mechanical shutter is opened and closed to control the exposure time of the photodiode 200 between time t11 and time t12 when signal accumulation of the photodiode 200 is accumulated. Further, the column circuit 104 is driven at time t12. From time t13 to time t14, readout of the imaging signal of the lowermost row at the screen edge is performed. The drive timing when reading the imaging signal is the same as the one-horizontal period driving timing chart (FIG. 3) when reading the imaging signal from the pixel unit 101 described above, and a description thereof will be omitted. At time t15, the readout of the imaging signals in the uppermost row at the screen edge is finished.

  The period during which the pixel portion 101 at the lower end of the screen is affected by the light emission of the column amplifier 209 is from time t12 to time t14. On the other hand, the period in which the pixel portion 101 at the upper end of the screen is affected by the light emission of the column amplifier 209 is from time t12 to time t15. Therefore, the pixel portion 101 at the upper end is longer than the lower end at the screen end by being affected by the light emission of the column amplifier 209. For this reason, the degree of whitening that occurs at the upper end of the screen edge is greater than that at the lower end.

  FIG. 5 is a block diagram illustrating an example of an image sensor according to the second embodiment. Unlike the first embodiment described with reference to FIG. 1, in the second embodiment, the entire horizontal width of the column circuit 104 arranged at the upper and lower portions of the screen end is made different between the upper portion and the lower portion. When all pixels are read sequentially after resetting all pixels, the image signal is read from the pixel unit 101 from the lower end toward the upper end, so that the pixel unit 101 arranged at the upper end read end position is arranged at the lower end. It takes more time to read out the image pickup signal than the pixel unit 101 that is present.

  Therefore, the horizontal width of the entire column circuit 104a at the upper read end position is made wider than the horizontal width of the entire lower column circuit 104b. Further, in the present embodiment, as in the first embodiment, the distance from the pixel unit 101 arranged at the upper and lower ends of the pixel array unit 102 to the column amplifier 209 that is a light emitting source arranged at the upper and lower ends is constant. The column circuit 104 is arranged so that Therefore, the degree of whitening caused by light emission from the column circuit can be made uniform near the center of the upper and lower ends of the screen and at the left and right ends.

  As described above, in each of the above embodiments, it is possible to make the degree of whitening near the center and the left and right ends of the upper and lower ends of the screen uniform by making the influence of the light emission of the column amplifier 209 uniform. . By making the degree of whitening uniform, one-dimensional shading occurs in the screen. However, as described above, the process for correcting one-dimensional shading can be performed more easily than the processing time for correcting two-dimensional shading. By this correction processing, an image sensor that suppresses deterioration in image quality can be provided.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  In this embodiment, the light source is described as the column amplifier 209, but another circuit in the column circuit 104 may be the light source.

  In this embodiment, each embodiment has been described using the readout circuit 106 configured by an analog circuit. However, the readout circuit may have a configuration including a column parallel A / D circuit that performs analog-digital conversion for each column. In the first embodiment, the configuration in which the column circuits 104 are arranged at the upper and lower portions of the screen edge has been described. However, the column circuits 104 may be arranged only at one of the screen edges. Even in this case, an effect equivalent to that of the first embodiment described above can be obtained at one of the screen edges.

100 image sensor, 101 pixel unit, 102 pixel array unit, 103 vertical output line,
104 column circuit, 105 load current source, 106 readout circuit,
107 column selection switch, 108 column selection switch, 109 vertical scanning circuit,
110 horizontal scanning circuit, 111 horizontal output line, 112 horizontal output line,
113 output amplifier, 114 reset switch, 115 reset switch

Claims (4)

A pixel array unit in which unit pixels each including a plurality of photoelectric conversion elements are arranged in a matrix;
A plurality of column circuits driven in association with the operation of reading out the imaging signal of the pixel array unit for each column of the pixel array unit;
The imaging device, wherein the pixel array section and the plurality of column circuits are arranged so that a horizontal width of the entire plurality of column circuits is wider than a horizontal width of the pixel array section. The pixel array section and the plurality of column circuits are arranged so that a distance between the unit pixel and the column circuit for reading an imaging signal of the unit pixel is constant in each column. The imaging device according to 1.   The imaging device according to claim 2, wherein the plurality of column circuits are arranged on both sides of one side of the pixel array unit and one side facing the side.   The image pickup device has a vertical scanning circuit that drives to sequentially read out the image pickup signal of the pixel array unit for each row, and the horizontal width of the plurality of column circuits arranged on the side to finish the read operation is The imaging device according to claim 3, wherein the imaging element is larger than a width of the whole of the plurality of column circuits arranged on a side on which a signal reading operation is started.