JP2018170703A - Imaging device, imaging apparatus, and method for controlling imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device, an imaging apparatus, and a method for controlling the imaging device, which allow for reduction in influence of coupling upon AD conversion of a pixel signal.SOLUTION: The imaging device is provided that comprises: a pixel array in which pixels outputting pixel signals are arranged in a matrix; a plurality of reference signal generating circuits generating a plurality of reference signals including at least a first reference signal and a second reference signal different from each other; and a first comparator and a second comparator each of which compares a pixel signal and a reference signal for each column, the first comparator receiving as input, a first reference signal, the second comparator receiving as input, a second reference signa. At least one of the first reference signal and the second reference signal are changed between lines or between frames.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a noise reduction technique when a pixel signal is read out in an imaging device and an imaging apparatus.

  As an AD conversion (Analog to Digital Convert) method for reading out a pixel signal in an imaging device such as a camera, in recent years, a column parallel AD conversion method that performs AD conversion in parallel for each column of pixels arranged in a matrix is used. Mainstream. For example, in a column parallel AD conversion method called a slope type, a pixel signal output from a pixel is compared with a slope-shaped reference signal. Then, the pixel signal is AD-converted by counting the time from when the output of the reference signal starts until the magnitude relationship between the pixel signal and the reference signal is reversed.

  However, in the normal column parallel AD conversion method, since the same reference signal is supplied to each column, when the difference in brightness of the optical image is small and the level of the pixel signal output from the pixel is approximately equal, Multiple column comparators are inverted at the same timing. As a result, power supply fluctuation when the output of the comparator is inverted increases and couples with the reference signal, and pattern noise such as horizontal stripes, vertical stripes, and horizontal smear appears in the image. Such coupling becomes more prominent as the number of comparators that are simultaneously inverted increases.

  Therefore, in Patent Document 1, for example, by changing the output start timing of the reference signal input to the comparator in the adjacent column, the timing at which the output of the comparator in the adjacent column is inverted is shifted to reduce the influence of coupling. doing.

JP, 2015-104021, A

  However, in Patent Document 1, although the influence of coupling is reduced when the contrast of the optical image is small, the effect of shifting the output start timing of the reference signal is increased when the contrast of the optical image becomes large. It is canceled by the level difference of the pixel signal. As a result, there is still a problem that the comparators of a plurality of columns are inverted at the same timing, and pattern noise appears in the image.

  According to an aspect of the present invention, a plurality of reference signals including at least a first reference signal and a second reference signal that are different from each other, and a pixel array in which pixels that output pixel signals are arranged in a matrix. A reference signal generating circuit, a comparator for comparing the pixel signal and the reference signal for each column, a first comparator for inputting the first reference signal, and a second for inputting the second reference signal. The imaging device is characterized in that at least one of the first reference signal and the second reference signal is changed between rows or frames.

  According to another aspect of the present invention, the image sensor according to any one of claims 1 to 11 and an AE sensor that detects a light / dark difference of an optical image, the light / dark difference detected by the AE sensor. Accordingly, an imaging apparatus is provided that determines an offset of the first reference signal and an offset of the second reference signal.

  According to still another aspect of the present invention, a pixel array in which pixels that output pixel signals are arranged in a matrix and a plurality of reference signals including at least a first reference signal and a second reference signal that are different from each other are provided. A plurality of reference signal generation circuits to be generated, a comparator that compares a pixel signal and a reference signal for each column, a first comparator that inputs a first reference signal, and a second reference signal And a second comparator, comprising: a step of changing at least one of the first reference signal and the second reference signal between rows or frames. There is provided a method for controlling an imaging device.

  ADVANTAGE OF THE INVENTION According to this invention, the imaging device which can reduce the influence of the coupling at the time of AD-converting a pixel signal, an imaging device, and the control method of an imaging device are provided.

It is a block diagram showing typically the composition of the image sensor concerning a 1st embodiment. FIG. 3 is an equivalent circuit diagram schematically illustrating a configuration of a pixel unit included in a pixel of the image sensor according to the first embodiment. 6 is a timing chart illustrating a first pattern in a column direction of a reference signal in the image sensor according to the first embodiment. 6 is a timing chart showing a second pattern in the column direction of reference signals in the image sensor according to the first embodiment. It is a timing chart which shows the 3rd pattern of the column direction of the reference signal in the image sensor which concerns on 1st Embodiment. It is a figure which shows notionally the control method of the image pick-up element which concerns on 1st Embodiment. It is a figure which shows the example of the control method which changes the pattern of the reference signal in the image sensor which concerns on 1st Embodiment to a row direction. It is a figure which shows the example of the control method which changes the pattern of the reference signal in the image pick-up element which concerns on 2nd Embodiment to a row direction. It is a block diagram which shows roughly the structure of the imaging device which concerns on 3rd Embodiment. It is a flowchart which shows the control method of the image pick-up element which concerns on 3rd Embodiment. It is a figure which shows the example of the control method which changes the pattern of the reference signal in the image pick-up element which concerns on 4th Embodiment between frames.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment, In the range which does not deviate from the summary, it can change suitably. In addition, components having the same or corresponding functions in each drawing are denoted by the same reference numerals, and the description thereof may be omitted or simplified.

(First embodiment)
A display device according to the first embodiment will be described with reference to FIGS. FIG. 1 is a block diagram schematically showing the configuration of the image sensor according to the first embodiment. The display device of this embodiment includes a pixel array 100, a vertical scanning circuit 104, a column circuit 106, a reference signal generation circuit 110, a timing generator 117, a horizontal scanning circuit 118, and a signal processing circuit 120.

  The pixel array 100 includes pixels 101 arranged in a matrix. In FIG. 1, a total of four pixels 101 of the i-th row, the i + 1-th row, the j-th column, and the j + 1-th column are depicted, but the actual pixel array 100 has more pixels 101. . Here, the pixel 101 may be composed of a plurality of pixel units 200 (see FIG. 2). For example, in the Bayer array or the like, the adjacent pixel 101 in the j-th column and pixel 101 in the (j + 1) -th column in the same row are each configured by a plurality of pixel units 200 having color filters of different colors (spectral transmittance). Also good. The configuration of the pixel unit 200 will be described later with reference to FIG.

  The vertical scanning circuit 104 controls the pixels 101 by scanning the horizontal signal lines 103 provided for each row of the pixel array 100 for each row. At this time, the selection switch 206 (see FIG. 2) of the pixel 101 is controlled by the vertical scanning circuit 104 and connects the pixel 101 to the column circuit 106 provided for each column via the vertical signal line 105.

  The timing generator 117 controls the vertical scanning circuit 104, the column circuit 106, the reference signal generation circuit 110, and the horizontal scanning circuit 118. Specifically, the timing generator 117 controls the vertical scanning circuit 104 to output a control signal for controlling a transistor or the like in the pixel 101, or controls the reference signal generation circuit 110 to control the reference signal R1. , R2 is output.

  The reference signal generation circuit 110 generates reference signals R1 and R2 whose signal levels change monotonously with time. As the reference signal generation circuit 110, for example, a DAC (Digital to Analog Converter) can be used. For example, a slope signal or a ramp signal is used as the reference signals R1 and R2. As shown in FIG. 1, the imaging device of this embodiment includes two types of reference signal generation circuits 110 that generate different reference signals R1 and R2. The reference signals R1 and R2 are different from each other in output start timing, reference level, time change gradient, or a combination thereof.

  The column circuit 106 includes a comparator 107, a counter 108, and a latch 109. The pixel signal S1 output to the j-th column vertical signal line 105 and the reference signal R1 are input to the column circuit 106 in the j-th column. Further, the pixel signal S2 output to the j + 1-th column vertical signal line 105 and the reference signal R2 are input to the column circuit 106 in the j + 1-th column. In other columns, similar patterns of the reference signals R1 and R2 are input to the column circuit 106 every two columns.

  The comparator 107 in the j-th column compares the pixel signal S1 output to the vertical signal line 105 in the j-th column with the reference signal R1 output from the reference signal generation circuit 110, and outputs the comparison result. The counter 108 in the j-th column counts the time from when the reference signal generation circuit 110 starts outputting the reference signal R1 to when the output of the comparator 107 is inverted in units of clocks. The latch 109 in the j-th column holds the count value of the counter 108 as a digital signal. The same applies to the column circuit 106 in the (j + 1) -th column except that the pixel signal S2 and the reference signal R2 are input instead of the pixel signal S1 and the reference signal R1. In the other columns, the same processing as in the j-th column and the j + 1-th column is repeated every two columns.

  As described above, in the present embodiment, the reference signals R1 and R2 are made different in the column direction (horizontal direction) to form a predetermined pattern. The pattern in the column direction of the reference signals R1 and R2 is determined so that the number of comparators 107 that are inverted at the same timing when the AD conversion of the pixel signals S1 and S2 is reduced. For example, in FIG. 1, the reference signals R1 and R2 are different at least between adjacent columns. As a result, the number of comparators 107 that are inverted at the same timing is halved.

  The horizontal scanning circuit 118 scans the column circuit 106 in the column direction via the horizontal signal line 119, and sequentially outputs the digital signals held in the latch 109 of the column circuit 106 to the signal processing circuit 120. The output digital signal is subjected to predetermined processing in the signal processing circuit 120.

  FIG. 2 is an equivalent circuit diagram schematically showing the configuration of the pixel unit 200 included in the pixel 101 of the image sensor according to the first embodiment. A pixel unit 200 includes a photoelectric conversion unit 201, a transfer switch 202, a floating diffusion region 203, a reset switch 204, a pixel amplifier 205, and a selection switch 206.

  The photoelectric conversion unit 201 includes a photodiode or the like that photoelectrically converts incident light, and accumulates signal charges generated by the photoelectric conversion. The transfer switch 202 is controlled by the transfer pulse PTX and transfers the signal charge accumulated in the photoelectric conversion unit 201 to the floating diffusion region 203. The reset switch 204 is controlled by the reset pulse PRES and discharges the signal charge held in the floating diffusion region 203. The pixel amplifier 205 is a source follower circuit including a MOS transistor and a constant current source. The selection switch 206 is controlled by the selection pulse PSEL, and outputs the output of the pixel amplifier 205 to the column circuit 106 via the vertical signal line 105. Here, the transfer pulse PTX, the reset pulse PRES, and the selection pulse PSEL are output from the vertical scanning circuit 104 shown in FIG.

  As described above with reference to FIGS. 1 and 2, in the imaging device of this embodiment, the reference signals R <b> 1 and R <b> 2 are made different in the column direction. As a result, the number of comparators 107 that are inverted at the same timing is reduced, so that the influence of coupling can be reduced. However, as described above, the effect of coupling is reduced when the contrast of the optical image is small, but the effect of shifting the output start timing of the reference signal is increased when the contrast of the optical image becomes large. It is canceled by the level difference between the pixel signals S1 and S2.

  More specifically, the output of the comparator 107 in the j-th column shown in FIG. 1 is inverted when the reference signal R1 and the pixel signal S1 become equal. The output of the comparator 107 in the j + 1-th column is inverted when the reference signal R2 and the pixel signal S2 become equal. When the contrast of the optical image is small, the level of the pixel signal S1 and the level of the pixel signal S2 are substantially equal. Therefore, by making the reference signal R1 and the reference signal R2 different, the comparator 107 in the jth column and the j + 1th column. The timing at which the comparator 107 is inverted can be shifted.

  However, when the light / dark difference of the optical image becomes large and the level difference between the pixel signal S1 and the pixel signal S2 becomes approximately the same as the level difference between the reference signal R1 and the reference signal R2, the level difference between the reference signal R1 and the reference signal R2 Is canceled by the level difference between the pixel signal S1 and the pixel signal S2. As a result, the comparator 107 in the j-th column and the comparator 107 in the j + 1-th column are inverted at the same timing.

  Therefore, in this embodiment, the reference signals R1 and R2 are made different in the column direction to form a predetermined pattern, and the pattern in the column direction is also changed in the row direction (vertical direction). Thus, since the output start timing of the reference signal is different in the row direction, for example, even when the comparators 107 of a plurality of columns are inverted at the same timing in the i-th row, they are inverted at the same timing in the i + 1-th row. The number of comparators 107 can be reduced. As a result, it is possible to avoid the occurrence of coupling in a plurality of rows in the same manner.

  3 to 5 are diagrams illustrating examples of the pattern in the column direction of the reference signals R1 and R2 that can be used in combination when the pattern in the column direction of the reference signals R1 and R2 is changed in the row direction. 3 to 5 show the pixel signals S1 and S2 and the reference signals R1 and R2 input to the comparator 107, the output of the comparator 107, and the counter value of the counter 108. 3 to 5 show timing charts when performing CDS (correlated double sampling).

  FIG. 3 is a timing chart showing a first pattern in the column direction of the reference signals R1 and R2 in the image sensor according to the first embodiment. In FIG. 3, the reset pulse PRES is set to Hi in advance to initialize the pixel 101 so that signal charges generated in the pixel 101 can be accumulated. While signal charges are accumulated in the pixel 101, the reset pulse PRES is Hi and the transfer pulse PTX is Lo.

  By time t300, the reset pulse PRES is set to Lo and the reset of the pixel 101 is released. Further, the selection pulse PSEL in the i-th row is set to Hi, and the pixels 101 in the i-th row are connected to the vertical signal line 105. As a result, the pixel signal S1 (N conversion) based on the signal charge amount held in the floating diffusion region 203 of the pixel 101 in the i-th row and j-th column after the reset is released becomes a comparator in the j-th column at time t300. 107 is input. Similarly, in the adjacent j + 1th column, the pixel signal S2 (N conversion) based on the signal charge amount held in the floating diffusion region 203 of the pixel 101 in the i-th row and j + 1-th column after reset is released is the j + 1th column. Is input to the comparator 107.

  At time t301, the reference signal generation circuit 110 in the j-th column starts outputting the reference signal R1 whose magnitude changes monotonically with time. At the same time, the counter 108 in the j-th column starts counting. Similarly, at time t302, the reference signal generation circuit 110 in the (j + 1) th column starts outputting the reference signal R2, and the counter 108 in the (j + 1) th column starts counting at the same time in the adjacent j + 1th column.

  At time t303, the magnitude relationship between the pixel signal S1 and the reference signal R1 is reversed, and the output of the comparator 107 in the j-th column is inverted. As a result, the counter value of the counter 108 in the j-th column is held in the latch 109 in the j-th column. Thereafter, when the reference signal R1 reaches a predetermined maximum value (or minimum value) at time t305, the digital value held in the latch 109 in the j-th column is output under the control of the horizontal scanning circuit 118. Similarly, at time t304, the magnitude relationship between the pixel signal S2 and the reference signal R2 is reversed, and the counter value of the counter 108 in the j + 1th column is held in the latch 109 in the j + 1th column. Thereafter, when the reference signal R2 reaches a predetermined maximum value (or minimum value) at time t306, the digital value held in the latch 109 in the j + 1-th column is output under the control of the horizontal scanning circuit 118. In this way, the pixel signals S1 and S2 (N conversion) from the pixel 101 are read out.

  At time t307, the comparator 107 is reset and the transfer pulse PTX is set to Hi, and the signal charge is transferred from the photoelectric conversion unit 201 of the pixel 101 to the floating diffusion region 203. As a result, the pixel signal S1 (S conversion) based on the signal charge amount transferred to the floating diffusion region 203 of the pixel 101 in the i-th row and j-th column is input to the comparator 107 in the j-th column. Similarly, the pixel signal S2 (S conversion) based on the signal charge amount transferred to the floating diffusion region 203 of the pixel 101 in the i-th row and the (j + 1) -th column is also converted to the comparator 107 in the (j + 1) -th column. Is input.

  At time t308, the reference signal generation circuit 110 in the j-th column starts outputting the reference signal R1 whose magnitude changes monotonically with time. At the same time, the counter 108 in the j-th column starts counting. Similarly, at time t309, the reference signal generation circuit 110 in the (j + 1) th column starts outputting the reference signal R2 and the counter 108 in the (j + 1) th column starts counting at the adjacent j + 1th column.

  At time t310, the magnitude relationship between the pixel signal S1 and the reference signal R1 is reversed, and the output of the comparator 107 in the j-th column is inverted. As a result, the counter value of the counter 108 in the j-th column is held in the latch 109 in the j-th column. Thereafter, when the reference signal R1 reaches a predetermined maximum value (or minimum value) at time t312, the digital value held in the latch 109 in the j-th column is output under the control of the horizontal scanning circuit 118. Similarly, at time t311, the magnitude relationship between the pixel signal S2 and the reference signal R2 is reversed, and the counter value of the counter 108 in the j + 1th column is held in the latch 109 in the j + 1th column. Thereafter, when the reference signal R2 reaches a predetermined maximum value (or minimum value) at time t313, the digital value held in the latch 109 of the j + 1-th column is output under the control of the horizontal scanning circuit 118. In this way, the pixel signals S1 and S2 (S conversion) from the pixel 101 are read out.

  Thereafter, the signal processing circuit 120 performs predetermined image processing such as subtracting the pixel signals S1 and S2 (N conversion) from the pixel signals S1 and S2 (S conversion).

  In FIG. 3, the reference signal R <b> 2 input to the comparator 107 in the j + 1-th column is coupled due to the inversion of the comparator 107 in the j-th column. Similarly, the reference signal R1 input to the comparator 107 in the j-th column is coupled due to the inversion of the comparator 107 in the j + 1-th column. As a result, the levels of the reference signals R1 and R2 fluctuate at time t303 (time t310) and time t304 (time t311).

  However, in this embodiment, the output start time t302 (time t309) of the reference signal R2 is shifted by a time difference t302-t301 with respect to the output start time t301 (time t308) of the reference signal R1. Further, the time difference t309-t308 is shifted by the same time difference t302-t301. Thereby, as shown in FIG. 3, it is possible to avoid the power supply fluctuation at time t303 (time t310) from being superimposed on the power supply fluctuation at time t304 (time t311), thereby reducing the influence of coupling. .

  In FIG. 3, the output start timing is different between the reference signal R1 and the reference signal R2, but the present invention is not limited to this. For example, the reference signals R1 and R2 may be ramp signals, and the standard level of the ramp waveform, the slope of time change, or a combination thereof may be varied. The slope of the ramp waveform over time can be adjusted by changing the DAC constant current or resistance value of the reference signal generation circuit 110. In this case, it is desirable to correct the difference in DAC output bit accuracy (resolution) and AD conversion gain by subsequent processing. It is also possible to make the slope of the temporal change of one ramp waveform of the reference signals R1 and R2 negative.

  Further, in the present embodiment, not only the reference signals R1 and R2 are made different in the column direction to form a predetermined pattern, but also the pattern in the column direction is changed in the row direction (vertical direction). Hereinafter, the second and third patterns that can be used in combination with the first pattern shown in FIG. 3 in order to change the pattern of the reference signals R1 and R2 in the row direction will be described.

  FIG. 4 is a timing chart showing a second pattern in the column direction of the reference signals R1 and R2 in the image sensor according to the first embodiment. In the second pattern of the reference signals R1 and R2 shown in FIG. 4, the time difference t402-t401 from the output start time t401 of the reference signal R1 to the output start time t402 of the reference signal R2 is changed to the time difference t302-t301 shown in FIG. It is bigger. The same applies to the time difference t409-t408. Others are the same as the first patterns of the reference signals R1 and R2 shown in FIG.

  The first pattern shown in FIG. 3 and the second pattern shown in FIG. 4 are combined to change the column direction pattern of the reference signals R1 and R2 in the row direction. For example, in the i-th row, the reference signals R1, R2 are changed in the column direction in the first pattern shown in FIG. 3, and in the i + 1-th row, the reference signals R1, R2 are arranged in the column in the second pattern shown in FIG. Change direction.

  In this way, by changing the pattern in the column direction of the reference signals R1 and R2 in the row direction, for example, even when the comparators 107 of a plurality of columns are inverted at the same timing in the i-th row, the same in the i + 1-th row. The number of comparators 107 that are inverted at the timing can be reduced. As a result, it is possible to avoid the occurrence of coupling in a plurality of rows in the same manner.

  Such a combination of the first pattern and the second pattern of the reference signals R1 and R2 is particularly effective when the color filters are different between adjacent columns in the same row as in the Bayer array. For example, it is assumed that a green (G) color filter is formed on the pixel 101 in the j-th column and a red (R) color filter is formed on the pixel 101 in the j + 1-th column. In this case, when white light is incident, generally, the pixel signal S2 output from the pixel 101 in the (j + 1) th column is smaller than the pixel signal S1 output from the pixel 101 in the jth column. 3 and 4, such a pixel signal S2 is indicated by a broken line (note that the magnitude of the pixel signal S2 is negative in FIGS. 3 and 4).

  Accordingly, when the spectral transmittance of the color filter of the pixel 101 is different between columns, the pattern in the column direction of the reference signals R1 and R2 is determined according to the spectral transmittance of the color filter, so that the same in a plurality of rows. Thus, the occurrence of coupling can be avoided.

  FIG. 5 is a timing chart showing a third pattern in the column direction of the reference signals R1 and R2 in the image sensor according to the first embodiment. In the third pattern of the reference signals R1 and R2 shown in FIG. 5, the order of the output start times of the reference signals R1 and R2 is reversed from the order of the reference signals R1 and R2 output start times shown in FIG. Others are the same as the first patterns of the reference signals R1 and R2 shown in FIG.

  The patterns of the reference signals R1 and R2 shown in FIG. 5 can be combined with the patterns of the reference signals R1 and R2 shown in FIGS. 3 and 4 to change the pattern in the column direction of the reference signals R1 and R2 in the row direction. Is possible. For example, in the i-th row, the reference signals R1 and R2 are changed in the column direction in the first pattern shown in FIG. 3, and in the i + 1-th row, the reference signals R1 and R2 are arranged in the column in the third pattern shown in FIG. Change direction. Thereby, the same effect as the case where the 1st pattern shown in above-mentioned FIG. 3 and the 2nd pattern shown in FIG. 4 are combined can be acquired.

  FIG. 6 is a diagram conceptually illustrating the control method of the image sensor according to the first embodiment. FIG. 6 shows the pixel array 100 shown in FIG. As described with reference to FIG. 1, the pixels 101 are arranged in a matrix in the pixel array 100, and the pixel signal output from each pixel is scanned in the row direction (vertical direction) shown in FIG. 6 by scanning of the horizontal scanning circuit 118. Read out.

  FIG. 6 shows an example in which the i-th row is read using the first pattern shown in FIG. 3 and the next i + 1-th row is read using the second pattern shown in FIG. Similarly, in the other rows, the first and second patterns are alternately repeated. In this way, the reference signals R1 and R2 are made different from each other in the column direction to form a predetermined pattern, and the pattern in the column direction is also changed in the row direction, so that a plurality of rows can be used regardless of the contrast of the optical image. Similarly, the occurrence of coupling can be avoided.

  In FIG. 6, the first pattern shown in FIG. 3 and the second pattern shown in FIG. 4 are combined. However, the patterns in the row direction of the reference signals R1 and R2 are optimal according to the shooting conditions. Should be selected. For example, as described above, the pattern in the column direction of the reference signals R1 and R2 may be determined according to the spectral transmittance of the color filter of the pixel 101, or an optical image as described in the fourth embodiment later. The pattern in the column direction of the reference signals R1 and R2 may be determined according to the brightness difference. Hereinafter, some examples of control methods for changing the patterns of the reference signals R1 and R2 in the row direction will be described.

  FIG. 7 is a diagram illustrating an example of control methods M1 to M4 for changing the pattern of the reference signals R1 and R2 in the row direction in the image sensor according to the first embodiment. In FIG. 7, the first to third patterns of the reference signals R1 and R2 shown in FIGS. 3 to 5 are expressed as patterns P1 to P3, respectively.

  In the following description, it is assumed that the reference signals R1 and R2 are ramp signals and the offsets of the output start times of the reference signals R1 and R2 are different from each other. However, the present embodiment is not limited to this. For example, instead of the offset of the output start time of the reference signals R1 and R2, the reference level of the reference signals R1 and R2 or the offset of the slope of the time change is made different from each other. Also good. The unit of the offset shown in FIG. 7 is an arbitrary unit. For example, when the output start times of the reference signals R1 and R2 are different, the unit is seconds and the reference levels of the reference signals R1 and R2 are different. Is a unit of voltage or the like. In FIG. 7, it is assumed that the offsets of the reference signals R1 and R2 take discrete four-level values. However, the present invention is not limited to this. For example, the offsets of the output start times of the reference signals R1 and R2 are arbitrary real values. A numerical value may be taken.

  The control method M1 schematically represents the control method of the image sensor shown in FIG. 6, and the pattern P1 in FIG. 3 and the pattern P2 in FIG. 4 are alternately repeated. Specifically, in the i-th row, the offset of the reference signals R1 and R2 is set to the pattern P1 = (1,2). In the next i + 1th row, the offset of the reference signals R1 and R2 is set to pattern P2 = (1, 4). Similarly, the pattern P1 and the pattern P2 are alternately repeated in the other rows. That is, in the control method M1, one of the offsets of the reference signals R1 and R2 is changed between the previous and next rows, and the pattern of the reference signals R1 and R2 is changed in the row direction.

  Next, in the control method M2, the pattern P1 in FIG. 3 and the pattern P3 in FIG. 5 are alternately repeated. Specifically, in the i-th row, the offset of the reference signals R1 and R2 is set to the pattern P1 = (1,2). In the next i + 1th row, the offset of the reference signals R1, R2 is set to pattern P3 = (2, 1). Similarly, the pattern P1 and the pattern P3 are alternately repeated in the other rows. That is, in the control method M2, the pattern of the reference signals R1 and R2 is changed in the row direction by reversing the order of the offsets of the reference signals R1 and R2 between the previous and next rows.

  Next, in the control method M3, the patterns P1 to P3 in FIGS. 1 to 3 and the pattern P4 (not shown) are repeated every four rows. Specifically, in the i-th row, the offset of the reference signals R1 and R2 is set to the pattern P1 = (1,2). In the next i + 1th row, the offset of the reference signals R1 and R2 is set to pattern P2 = (1, 4). In the next i + 2th row, the offset of the reference signals R1 and R2 is set to pattern P4 = (4, 1). In the next i + 3th row, the offset of the reference signals R1, R2 is set to pattern P3 = (2, 1). Similarly, the patterns P1 to P4 are repeated every four rows in the other rows. That is, in the control method M3, the pattern of the reference signals R1 and R2 is changed by changing one of the offsets of the reference signals R1 and R2 between the preceding and succeeding rows or by reversing the order of the offsets of the reference signals R1 and R2. The direction is changed.

  Next, in the control method M4, the patterns P1 to P3 in FIGS. 1 to 3 and the patterns P4 to P6 (not shown) are repeated every six rows. Specifically, in the i-th row, the offset of the reference signals R1 and R2 is set to the pattern P1 = (1,2). In the next i + 1th row, the offset of the reference signals R1 and R2 is set to pattern P4 = (4, 1). In the next i + 2th row, the offset of the reference signals R1 and R2 is set to pattern P2 = (1, 4). In the next i + 3th row, the offset of the reference signals R1, R2 is set to pattern P3 = (2, 1). In the next i + 4th row, the offset of the reference signals R1 and R2 is set to pattern P5 = (1, 3). In the next i + 5th row, the offset of the reference signals R1, R2 is set to pattern P6 = (3, 1). Similarly, the patterns P1 to P6 are repeated every six rows in the other rows. That is, in the control method M4, one of the offsets of the reference signals R1 and R2 is changed between the preceding and succeeding rows, and the order of the offsets of the reference signals R1 and R2 is reversed to change the pattern of the reference signals R1 and R2 in the row direction. It is changing.

  As described above, in this embodiment, a plurality of reference signal generation circuits that generate a plurality of reference signals including at least the first reference signal (R1) and the second reference signal (R2) that are different from each other, the pixel signal, And a comparator for comparing the reference signal for each column. At least one of the first reference signal (R1) and the second reference signal (R2) is changed between rows. With such a configuration, an imaging device capable of reducing the influence of coupling when the pixel signal is AD converted, and a control method thereof are provided.

  Note that the change in changing the pattern of the reference signals R1 and R2 in the row direction is not necessarily periodic. For example, it may be changed randomly using a random number or the like. Further, the change in changing the pattern of the reference signals R1 and R2 in the row direction is not necessarily in units of rows, and may be changed in units of a plurality of rows, for example, and will be described later in the fourth embodiment. It is also possible to change between frames. Further, the same pattern in the column direction of the reference signals R1 and R2 may be shifted in the row direction by shifting by a predetermined phase difference.

(Second Embodiment)
An image sensor and a control method thereof according to the second embodiment will be described with reference to FIG. FIG. 8 is a diagram illustrating an example of control methods M5 to M6 for changing the pattern of the reference signals R1 and R2 in the row direction in the image sensor according to the second embodiment. The image sensor of this embodiment includes four types of reference signal generation circuits 110 that generate different reference signals R1 to R4. Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  In the control method M5, the pattern P7 and the pattern P8 are alternately repeated in the row direction. Here, the patterns P7 and P8 are the predetermined patterns shown in FIG. 8 including the reference signals R1 to R4. Specifically, in the i-th row, the offset of the reference signals R1 to R4 is set to pattern P7 = (1, 2, 3, 4). In the next i + 1th row, the offset of the reference signals R1 to R4 is set to pattern P8 = (4, 3, 2, 1). Similarly, the pattern P7 and the pattern P8 are alternately repeated in the other rows. That is, in the control method M5, the pattern of the reference signals R1 to R4 is changed in the row direction by reversing the order of the offsets of the reference signals R1 to R4 between the previous and next rows.

  Next, in the control method M6, the patterns P9 to P14 are repeated every six rows. Here, the patterns P9 to P14 are the predetermined patterns shown in FIG. 8 including the reference signals R1 to R4. Specifically, in the i-th row, the offset of the reference signals R1 to R4 is a pattern P9 = (1, 2, 3, 4). In the next i + 1th row, the offset of the reference signals R1 to R4 is set to pattern P10 = (3, 4, 1, 2). In the next i + 2th row, the offset of the reference signals R1 to R4 is set to pattern P11 = (2, 1, 4, 3). In the next i + 3th row, the offset of the reference signals R1 to R4 is set to pattern P12 = (4, 3, 2, 1). In the next i + 4th row, the offset of the reference signals R1 to R4 is set to pattern P13 = (1, 3, 2, 4). In the next i + 5th row, the offset of the reference signals R1 to R4 is set to pattern P14 = (4, 2, 3, 1). Similarly, the patterns P9 to P14 are repeated every six rows in the other rows. That is, in the control method M6, the offset of the reference signal of at least half of the reference signals R1 to R4 in the patterns P9 to P14 is changed by more than a half of the maximum change amount of the offset (= 4) between the previous and next rows. .

  As described above, the present embodiment includes a plurality of reference signal generation circuits that generate different reference signals R1 to R4. The offset pattern in the column direction of the different reference signals R1 to R4 is changed between the rows. As a result, the period of the pattern in the column direction of the offset of the reference signals R1 to R4 becomes longer, and the number of comparators that are inverted at the same timing is reduced, so that the influence of coupling can be further reduced. In FIG. 8, four types of different reference signals R1 to R4 are used, but the present invention is not limited to this. Different kinds of reference signals may be natural numbers of 2 or more.

  Further, as in the control method M6 in FIG. 8, the period when the pattern of the reference signals R1 to R4 is changed in the row direction is made longer, so that the number of rows in which the comparator 107 is inverted at the same timing is reduced. The influence of the ring can be further reduced.

(Third embodiment)
An imaging apparatus including an imaging device according to the third embodiment and a control method thereof will be described with reference to FIGS. 9 and 10. FIG. 9 is a block diagram schematically showing the configuration of the imaging apparatus 1009 according to the third embodiment. An imaging apparatus 1009 of this embodiment includes an imaging device 1000, a photographing lens 1001, a lens driving circuit 1002, an overall control / arithmetic circuit 1003, an AE sensor 1004, a memory 1005, a recording circuit 1006, an operation circuit 1007, and a display circuit 1008. Configured.

  The taking lens 1001 forms an optical image of a subject on the image sensor 1000. A lens driving circuit 1002 drives the photographing lens 1001 for focus control and the like. The image sensor 1000 is the image sensor according to the first or second embodiment shown in FIG. 1, and captures and outputs an optical image. The memory 1005 temporarily stores image data output from the image sensor 1000. The recording circuit 1006 is a detachable semiconductor memory or the like, and records image data. The operation circuit 1007 receives an operation by the photographer using an operation member. The display circuit 1008 displays various information and captured images. The overall control / arithmetic circuit 1003 performs various arithmetic processes and controls the entire imaging apparatus.

  The AE sensor 1004 is a multi-division sensor that can identify the lightness and darkness and color of the subject. In the present embodiment, the AE sensor 1004 detects the lightness and darkness difference of the optical image. Then, an offset of the reference signal is determined in accordance with the detected contrast of the optical image in the column direction of the subject. At this time, the light-dark difference in the column direction of the optical image may be obtained as a difference between the maximum value and the minimum value of the luminance of the optical image of the subject, or may be obtained as a variance value of the luminance of the optical image.

  FIG. 10 is a flowchart illustrating a method for controlling the image sensor according to the third embodiment. In step S101, the AE sensor 1004 detects the contrast of the optical image of the subject. In step S102, when the detected contrast is equal to or greater than the predetermined threshold (Yes), the process proceeds to step S103, and when it is less than the predetermined threshold (No), the process proceeds to step S104.

  In step S103, the overall control / arithmetic circuit 1003 determines to change the offset of the reference signals R1 to R4 in the row direction. In step S105, a control method for changing the offsets of the reference signals R1 to R4 in the row direction according to the contrast of the subject is determined. Then, the process proceeds to step S106. On the other hand, in step S104, the overall control / arithmetic circuit 1003 determines not to change the offsets of the reference signals R1 to R4 in the row direction. Then, the process proceeds to step S106.

  In step S106, the image sensor 1000 reads out a pixel signal. In step S107, predetermined image processing is performed on the read pixel signal, and the obtained image is displayed on the display circuit 1008 or output to the recording circuit 1006, and the photographing is finished.

  As described above, the present embodiment includes the above-described imaging device and the AE sensor that detects the light / dark difference of the optical image. Then, the offset of the reference signal is determined according to the light / dark difference detected by the AE sensor. With such a configuration, an imaging device, an imaging device, and an imaging device control method capable of reducing the influence of coupling when the pixel signal is AD-converted are provided.

(Fourth embodiment)
An imaging device and a control method thereof according to the fourth embodiment will be described with reference to FIG. In the first embodiment, the offsets of the reference signals R1 and R2 are changed between rows. On the other hand, in this embodiment, the offsets of the reference signals R1 and R2 are changed between frames. Since others are generally the same as those in the first embodiment, description thereof is omitted.

  FIG. 11 is a diagram illustrating an example of control methods M7 to M10 for changing the offsets of the reference signals R1 and R2 in the imaging device according to the fourth embodiment between frames. In the control methods M7 to M10 shown in FIG. 11, the offsets of the reference signals R1 and R2 of the control methods M1 to M4 shown in FIG. 7 of the first embodiment are changed not between the rows but between the preceding and following frames. Yes. Accordingly, FIG. 11 shows the frame number k instead of the row number i shown in FIG.

  Thereby, for example, in multiple exposure photography or HDR (High Dynamic Range) photography in which optical images of the same subject are superimposed, it is possible to suppress the superposition of influences due to coupling. Similarly, even in a configuration including three or more reference signal generation circuits 110 shown in FIG. 8 of the first embodiment, the offset of the reference signal can be changed between frames. Further, the offset of the reference signal may be changed both between rows and between frames.

  As described above, in this embodiment, a plurality of reference signal generation circuits that generate a plurality of reference signals including at least the first reference signal (R1) and the second reference signal (R2) that are different from each other, the pixel signal, And a comparator for comparing the reference signal for each column. At least one of the first reference signal (R1) and the second reference signal (R2) is changed between frames. With such a configuration, it is possible to suppress superposition of influence due to coupling in multiple exposure photography, HDR photography, and the like.

(Other embodiments)
The present invention is not limited to the above embodiment, and various modifications can be made. For example, the configuration of the imaging apparatus described in the above embodiment is an example, and the imaging apparatus to which the present invention is applicable is not limited to such a configuration.

  The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

  For example, delaying the output start times of the reference signals R1 and R2 may increase the readout time and reduce the margin for the dark current of the image sensor. Further, since the noise of the image sensor increases as the ISO sensitivity increases, the coupling noise in the comparator 107 becomes relatively inconspicuous. Therefore, the present invention may be implemented only in the case of low ISO sensitivity or multiple exposure shooting. The above-described embodiments can be applied in combination.

100: pixel array 101: pixel 104: vertical scanning circuit 105: vertical signal line 106: column circuit 107: comparator 108: counter 109: latch 110: reference signal generating circuit 117: timing generator 118: horizontal scanning circuit 119: horizontal signal Line 120: Signal processing circuit 1000: Image sensor 1001: Shooting lens 1004: AE sensor

Claims (16)

A pixel array in which pixels that output pixel signals are arranged in a matrix;
A plurality of reference signal generation circuits for generating a plurality of reference signals including at least a first reference signal and a second reference signal different from each other;
A comparator for comparing the pixel signal and the reference signal for each column, the first comparator for inputting the first reference signal, and the second comparator for inputting the second reference signal. When,
With
An image sensor, wherein at least one of the first reference signal and the second reference signal is changed between rows or frames. The image sensor according to claim 1, wherein the first reference signal and the second reference signal have different output start timings. The imaging device according to claim 1, wherein the first reference signal and the second reference signal have different reference levels. The imaging device according to claim 1, wherein the first reference signal and the second reference signal are ramp signals, and have different slopes of change with time. 5. The image sensor according to claim 1, wherein at least one of the first reference signal and the second reference signal is changed both between rows and between frames. 6. 6. The image sensor according to claim 1, wherein at least one of the first reference signal and the second reference signal is randomly changed between rows or frames. 6. The image sensor according to any one of claims 1 to 6, wherein at least one of the first reference signal and the second reference signal is changed between front and rear rows or front and rear frames. The image sensor according to any one of claims 1 to 7, wherein a plurality of reference signal offset patterns in a column direction are changed between rows or frames. The imaging device according to claim 8, wherein the order of the offset of the reference signal in the pattern is reversed between the front and rear rows or the front and rear frames. The offset of the reference signal of at least half of the plurality of reference signals in the pattern is changed by more than half of the maximum offset change amount between the preceding and following rows or the preceding and following frames. The imaging device according to 9. The pixel has a color filter;
The image sensor according to any one of claims 8 to 10, wherein an offset of the reference signal is determined in accordance with a spectral transmittance of the color filter. The imaging device according to any one of claims 1 to 11,
An AE sensor that detects a difference in brightness of an optical image;
And an offset of the first reference signal and an offset of the second reference signal are determined in accordance with the brightness difference detected by the AE sensor. The at least one of the first reference signal and the second reference signal is changed between rows or frames when the brightness difference detected by the AE sensor is equal to or greater than a predetermined threshold value. Item 13. The imaging device according to Item 12. A pixel array in which pixels that output pixel signals are arranged in a matrix;
A plurality of reference signal generation circuits for generating a plurality of reference signals including at least a first reference signal and a second reference signal different from each other;
A comparator for comparing the pixel signal and the reference signal for each column, the first comparator for inputting the first reference signal, and the second comparator for inputting the second reference signal. When,
A method for controlling an imaging device comprising:
A method of controlling an image sensor, comprising: changing at least one of the first reference signal and the second reference signal between rows or frames. A pixel array in which pixels that output pixel signals are arranged in a matrix;
A plurality of reference signal generation circuits for generating a plurality of reference signals including at least a first reference signal and a second reference signal different from each other;
A comparator for comparing the pixel signal and the reference signal for each column, the first comparator for inputting the first reference signal, and the second comparator for inputting the second reference signal. When,
In an imaging device comprising:
A program for causing at least one of the first reference signal and the second reference signal to function as means for changing between rows or frames.   A computer-readable storage medium storing the program according to claim 15.

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