JP2011103530A - Image sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image sensor suppressing blooming from an exposure area to a light shielded area. <P>SOLUTION: The image sensor of a rolling shutter system has a pixel array section 11 and a control section 14. The pixel array section 11 is equipped with an exposure area and a light shielded area, and pixels are arranged in two-dimensional array to the vertical direction and the horizontal direction in the pixel array section 11. Each of boundary pixel arrays is a pixel array in parallel to the boundary between the exposure area and the light shielded area in the pixel array section 11, and the boundary pixel arrays are a plurality of pixel arrays including the boundary. The control section 14 establishes an address for each of boundary pixel arrays, and controls a boundary pixel array with the established address to perform shuttering by a predetermined time interval. The image senseor is applicable to a CMOS image sensor, for example. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image sensor, and more particularly to an image sensor that suppresses blooming from an exposure area to a light shielding area.

  In the pixel array part of CMOS (Complementary Metal Oxide Semiconductor) image sensors and CCD (Charge Coupled Device) image sensors, the exposure area (effective pixel area, effective pixel area that can output image signals among all pixels) In addition to a region (also referred to as a region), there is a light-shielding region (also referred to as an optical black pixel, optical black, or the like) that defines a black level reference.

  According to the light shielding region, by taking the difference between the signal component in the exposure region and the signal component in the light shielding region, it is possible to remove noise caused by dark current generated by heat regardless of incident light.

  By the way, in the image sensor, when the incident light is very strong or the pixel is not read out for a long time, the excessively accumulated charge overflows from the pixel (photodiode) and leaks to the adjacent pixel or signal line. So-called blooming may occur.

  In view of this, there is a technique in which blooming is avoided by performing a shutter for resetting accumulated charges for pixels that are not read out for a predetermined time (see Patent Document 1).

JP 2008-288904 A

  However, an effective countermeasure against blooming from the exposure area to the light shielding area that occurs in the pixel array portion having the exposure area and the light shielding area has not been proposed.

  When blooming from the exposure area to the light-shielding area occurs, the correct black level reference cannot be obtained.

  The present invention has been made in view of such a situation, and in particular, is intended to suppress blooming from an exposure area to a light shielding area.

  An image sensor according to one aspect of the present invention is a rolling shutter type image sensor in which pixels are two-dimensionally arranged in a vertical direction and a horizontal direction, and includes a pixel array unit including an exposure region and a light-shielding region. In the section, the address of a boundary pixel column, which is a pixel column aligned in parallel with the boundary between the exposure region and the light shielding region, and is a plurality of the pixel columns including the boundary, and the boundary where the address is set Control means for causing the pixel column to perform shutters at predetermined time intervals is provided.

  The control unit may cause the boundary pixel column to which an address is set to perform a shutter for each scanning period of a pixel column aligned in parallel with the boundary.

  The boundary pixel column may be a predetermined number of pixel columns arranged on the light shielding region side from the boundary.

  The boundary may be formed in a vertical direction or a horizontal direction in the pixel array unit.

  In one aspect of the present invention, in the pixel array unit, addresses of boundary pixel columns that are pixel columns aligned in parallel with the boundary between the exposure region and the light-shielding region and are a plurality of pixel columns including the boundary are set, and the address The shutter is performed at a predetermined time interval on the boundary pixel row where is set.

  According to one aspect of the present invention, it is possible to suppress blooming from an exposure region to a light shielding region.

It is a block diagram which shows the structural example of one Embodiment of the image sensor to which this invention is applied. It is a figure explaining the boundary of the light-shielding area | region and exposure area | region of a pixel array part. It is a figure explaining the operation | movement control of the lead | read | reed with respect to a pixel array part, and a shutter. It is a block diagram which shows the structural example of other embodiment of the image sensor to which this invention is applied. It is a figure explaining the boundary of the light-shielding area | region and exposure area | region of a pixel array part. It is a figure explaining the operation | movement control of the lead | read | reed with respect to a pixel array part, and a shutter.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The description will be given in the following order.
1. First embodiment (image sensor for reading and shuttering in units of rows)
2. Second embodiment (image sensor for reading and shuttering in units of columns)

<1. First Embodiment>
[Block diagram of image sensor]
FIG. 1 is a block diagram showing a configuration example of an embodiment of an image sensor to which the present invention is applied.

  The image sensor of FIG. 1 is configured as a CMOS image sensor, for example.

  The image sensor shown in FIG. 1 includes a pixel array unit 11, a pixel drive address decoder 12, a horizontal selection circuit 13, and a control unit 14.

  In the pixel array unit 11, photoelectric conversion elements (not shown) as pixels are two-dimensionally arranged in N rows in the vertical direction and M columns (N rows × M columns) in the horizontal direction. Each pixel of the pixel array unit 11 photoelectrically converts light incident thereon and outputs an imaging signal obtained as a result. The pixel array unit 11 includes an exposure region that is a region of a pixel that can output an imaging signal among all the pixels, and a light shielding region that defines a black level reference. As shown in FIG. 1, the light-shielding region in the pixel array unit 11 is provided so as to surround four directions in the top, bottom, left, and right of the exposure region.

  Based on the control of the control unit 14, the pixel drive address decoder 12 performs a charge reading operation (hereinafter also referred to as “read”) and a sweeping operation (hereinafter also referred to as “shutter”) of the pixels of the pixel array unit 11 in units of rows. The row in which the pixel array unit 11 is read and shuttered is sequentially shifted with time. That is, the image sensor of FIG. 1 is a rolling shutter type image sensor. The imaging signal output from each pixel in the row selected by the pixel drive address decoder 12 is supplied to the horizontal selection circuit 13.

  The horizontal selection circuit 13 includes therein an A / D (Analog to Digital) conversion circuit as many as the number M of pixels in the horizontal direction of the pixel array unit 11, and each A / D conversion circuit includes a pixel. CDS (Correlated Double Sampling) processing and A / D conversion processing are performed on the imaging signals supplied from the pixels of the array unit 11. The horizontal selection circuit 13 sequentially selects and reads out the imaging signals of the A / D conversion circuits and supplies them to an output amplifier circuit (not shown). An output amplifier circuit (not shown) amplifies the supplied imaging signal and outputs it.

  Note that the A / D conversion circuit of the horizontal selection circuit 13 may perform only CDS processing, and an AD converter that converts an analog signal into a digital signal may be provided before the output amplifier circuit (not shown).

  The control unit 14 controls the operation timing of the pixel drive address decoder 12 and the horizontal selection circuit 13. For example, the control unit 14 sets the row address of the row to be read and shuttered in the pixel array unit 11 performed by the pixel drive address decoder 12, and the pixel at the predetermined timing with respect to the pixel of the row address The drive address decoder 12 performs reading and shuttering.

[Boundary between shading area and exposure area]
Next, the boundary between the light shielding area and the exposure area of the pixel array unit 11 will be described with reference to FIG.

  FIG. 2 is an enlarged view of the upper left part of the pixel array unit 11 shown in FIG. As shown by a broken line in FIG. 2, in the pixel array unit 11, a pixel column arranged in parallel with a horizontal (row direction) boundary between the exposure region and the light shielding region, and a plurality of pixel columns including the boundary ( A region composed of a boundary pixel column) is defined as a boundary region.

  In FIG. 2, each pixel in the pixel array unit 11 is not shown, but if the input (arrow) from the pixel drive address decoder 12 corresponds to one pixel column in the horizontal direction, the boundary pixel column forming the boundary region is One pixel column in the light shielding region and one pixel column in the exposure region are adjacent to the boundary. However, one pixel column in the exposure region includes both ends thereof in the light shielding region.

  Note that the boundary pixel column forming the boundary region is not limited to the above-described example, and may be formed of a plurality of pixel columns including the boundary between the exposure region and the light shielding region. A three-pixel row and a three-pixel row in the exposure area may be used. Moreover, it is good also as a several pixel row | line | column arranged in a light-shielding area side from a boundary.

  Although not shown in FIG. 2, a boundary region exists at the boundary between the exposure region and the light shielding region on the lower side of the pixel array unit 11 in FIG. 1 as in FIG.

[Operation control of lead and shutter for pixel array section]
Next, with reference to FIG. 3, the read and shutter operation control for the pixel array unit 11 will be described.

  FIG. 3 shows a signal supplied from the control unit 14 to the pixel drive address decoder 12 for the pixel drive address decoder 12 to read and shutter the pixel array unit 11 and an address of the pixel column in the row direction (row address). ).

  The first from the top of FIG. 3 shows the vertical synchronization signal V used for synchronization of the vertical scanning period, and the second from the top of FIG. 3 shows the horizontal synchronization signal H used for synchronization of the horizontal scanning period. It is shown. FIG. 3 shows a horizontal synchronization signal H for two horizontal scanning periods, and scanning of two pixel columns in the horizontal direction (row direction) is performed during this period. Further, all pixel columns in the row direction are scanned in one vertical scanning period.

The third row from the top in FIG. 3 shows a read row address, which is a row address at which the pixel drive address decoder 12 performs a read operation (reading operation of pixel charges). The read row address is one for each horizontal scanning period of the horizontal synchronizing signal H from the row address indicating the top pixel column in the row direction of the pixel array unit 11 to the row address indicating the bottom pixel column. It is incremented (in FIG. 3 is incremented by 1 from the row address n _R).

The fourth from the top in FIG. 3 shows a normal shutter row address which is a row address at which the pixel drive address decoder 12 performs a shutter (a pixel charge sweeping operation). The normal shutter row address is 1 for each horizontal scanning period of the horizontal synchronizing signal H from the row address indicating the top pixel column in the row direction of the pixel array unit 11 to the row address indicating the bottom pixel column. It is incremented by (in FIG. 3 is incremented by 1 from the row address n _S). Normal shutter performed on pixel rows in a given row address n _S, from the time that the read is performed, is performed in the accumulation time (exposure time) minutes only before time charges (light). That is, in the example of FIG. 3, in the pixel array unit 11, towards the row address n _S is the pixel column indicated by the row address n _R than the pixel columns shown is that the underlying.

  In the fifth to eighth positions from the top in FIG. 3, the boundary area shutter row, which is a row address at which the pixel drive address decoder 12 performs a shutter (a charge discharging operation of the pixel) and is a row address of a boundary pixel column in the boundary area. The address is shown. The boundary area shutter row address is fixed regardless of the horizontal scanning period of the horizontal synchronization signal H. As described above, the boundary pixel column forming the boundary area described in FIG. 2 is set by the boundary area shutter row address. The boundary area shutter row address can be arbitrarily set by the user.

In FIG. 3, the row address N _B, the boundary indicates the row address of the first pixel th column of the light-blocking region side from the row address N _E is one pixel row of the row address of the exposure region side from the boundary Show. That is, the boundary pixel column set by the boundary region shutter row address in FIG. 3 includes two pixel columns of the light shielding region and two pixel columns of the exposure region adjacent to the boundary. As described above, the number of pixel columns constituting the boundary pixel column is not limited to the example of FIG.

  Here, when it is not necessary to distinguish between the normal shutter row address and the boundary area shutter row address, these are collectively referred to as a shutter row address hereinafter.

  The ninth pixel from the top (second from the bottom) in FIG. 3 shows a pixel read signal for instructing the pixel drive address decoder 12 to perform reading (reading operation of the charge of the pixel). The pixel read signal becomes a high level once every horizontal scanning period of the horizontal synchronization signal H.

  In other words, the pixel drive address decoder 12 reads the pixel at the read row address set at that time once per horizontal scanning period. Since the read row address is incremented by 1 for each horizontal scanning period of the horizontal synchronization signal H, the pixel drive address decoder 12 reads one row for each horizontal scanning period of the horizontal synchronization signal H.

  The pixel shutter signal for instructing the pixel drive address decoder 12 to perform the shutter (the operation of sweeping out the charge of the pixel) is shown in the tenth from the top (first from the bottom) in FIG. The pixel shutter signal becomes High level once every horizontal scanning period of the horizontal synchronization signal H.

  In other words, the pixel drive address decoder 12 performs shutter on the pixel of the shutter row address set at that time once in each horizontal scanning period. Since the normal shutter row address is incremented by 1 for each horizontal scanning period of the horizontal synchronization signal H, the pixel drive address decoder 12 performs shutter one row for each horizontal scanning period of the horizontal synchronization signal H.

  Further, since the boundary area shutter row address is fixed regardless of the horizontal scanning period of the horizontal synchronization signal H, the pixel drive address decoder 12 has a boundary that forms a boundary area for each horizontal scanning period of the horizontal synchronization signal H. Shutter is performed on all the pixels in the pixel column.

  According to the above configuration, the charges of the pixels included in the boundary region between the light shielding region and the exposure region are swept out at a certain interval (for example, one horizontal scanning period). Thus, even when charges overflow in the pixels in the exposure region, leakage of charges into the pixels in the light shielding region, that is, blooming can be suppressed. This makes it possible to stably obtain the correct black level reference.

  In the above description, the control unit 14 causes the shutter to be performed on all the pixels in the boundary region every horizontal scanning period of the horizontal synchronization signal H. However, the shutter is applied to the pixels in the boundary region. The time interval to be performed is not limited to this. More specifically, in FIG. 3, the pixel shutter signal is set to the High level once every horizontal scanning period of the horizontal synchronization signal H. However, the present invention is not limited to this, and every horizontal scanning period. The high level may be set a plurality of times, or the high level may be set once every a plurality of horizontal scanning periods. Further, the pixel shutter signal may be divided into a signal for performing a shutter for a pixel at a normal shutter row address and a signal for performing a shutter for a pixel at a boundary region shutter row address.

  In the above description, the read row address is incremented by 1 from the row address indicating the top pixel column in the row direction of the pixel array unit 11 to the row address indicating the bottom pixel column. All pixels in the pixel array unit 11 are read out. However, in the boundary region, for example, since a shutter is performed every horizontal scanning period, sufficient charges are not accumulated in the pixels included in the exposure region of the boundary region. Therefore, the boundary pixel column forming the boundary region may not be read.

  In the above description, the configuration in which reading and shuttering of the pixel array unit is performed in units of rows has been described. In the following, the configuration in which reading and shuttering of the pixel array unit is performed in units of columns will be described. In the following description, the description of the same functions and configurations as those described above will be omitted as appropriate.

<2. Second Embodiment>
[Block diagram of image sensor]
FIG. 4 is a block diagram showing a configuration example of another embodiment of an image sensor to which the present invention is applied.

  The image sensor of FIG. 4 is configured as a CMOS image sensor, for example.

  The image sensor shown in FIG. 4 includes a pixel array unit 111, a pixel drive address decoder 112, a vertical selection circuit 113, and a control unit 114.

  The pixel array unit 111 has a configuration similar to that of the pixel array unit 11 described in FIG.

  The pixel drive address decoder 112 performs a read operation (read) and a discharge operation (shutter) of the charges of the pixels of the pixel array unit 111 in units of columns based on the control of the control unit 114. The column in which reading and shuttering of the pixel array unit 111 is performed is sequentially shifted with time. That is, the image sensor in FIG. 4 is a rolling shutter type image sensor. The imaging signal output from each pixel in the column selected by the pixel drive address decoder 112 is supplied to the vertical selection circuit 113.

  The vertical selection circuit 113 includes therein an A / D conversion circuit as many as the number N of pixels in the vertical direction of the pixel array unit 111, and each A / D conversion circuit includes a pixel of the pixel array unit 111. CDS processing and A / D conversion processing are performed on the image pickup signal supplied from. The vertical selection circuit 113 sequentially selects and reads out the imaging signals of the A / D conversion circuits and supplies them to an output amplifier circuit (not shown). An output amplifier circuit (not shown) amplifies the supplied imaging signal and outputs it.

  Note that the A / D conversion circuit of the vertical selection circuit 113 may perform only CDS processing, and an AD converter that converts an analog signal into a digital signal may be provided before the output amplifier circuit (not shown).

  The control unit 114 controls the operation timing of the pixel drive address decoder 112, the vertical selection circuit 113, and the like. For example, the control unit 114 sets a column address of a column to be read and shuttered in the pixel array unit 111 performed by the pixel drive address decoder 112, and the pixel of the column address is set at a predetermined timing. The drive address decoder 112 performs reading and shuttering.

[Boundary between shading area and exposure area]
Next, the boundary between the light shielding region and the exposure region of the pixel array unit 111 will be described with reference to FIG.

  FIG. 5 is an enlarged view of the upper left part of the pixel array unit 111 shown in FIG. As indicated by a broken line in FIG. 5, in the pixel array unit 111, a pixel column that is arranged in parallel with a vertical direction (column direction) boundary between the exposure region and the light shielding region, and a plurality of pixel columns including the boundary ( A region composed of a boundary pixel column) is defined as a boundary region.

  In FIG. 5, each pixel in the pixel array unit 111 is not shown, but if the input (arrow) from the pixel drive address decoder 112 corresponds to one vertical pixel column, the boundary pixel column forming the boundary region is One pixel column in the light shielding region and one pixel column in the exposure region are adjacent to the boundary. However, one pixel column in the exposure region includes both ends thereof in the light shielding region.

  Note that the boundary pixel column forming the boundary region is not limited to the above-described example, and may be composed of a plurality of pixel columns including the boundary between the exposure region and the light shielding region.

  In addition, although not shown in FIG. 5, a boundary region exists at the boundary between the exposure region and the light shielding region on the right side of the pixel array unit 111 in FIG. 4 as in FIG.

[Operation control of lead and shutter for pixel array section]
Next, with reference to FIG. 6, the read and shutter operation control for the pixel array unit 111 will be described.

  FIG. 6 illustrates a signal supplied from the control unit 114 to the pixel drive address decoder 112 for the pixel drive address decoder 112 to read and shutter the pixel array unit 111 and an address of the pixel column in the column direction (column address). ).

  6 shows the horizontal synchronization signal H used for synchronization in the horizontal scanning period, and the second from the top in FIG. 6 shows the vertical synchronization signal V used for synchronization in the vertical scanning period. It is shown. FIG. 6 shows a vertical synchronization signal V for two vertical scanning periods, and scanning of two pixel columns in the vertical direction (column direction) is performed during this period. Further, all the pixel columns in the column direction are operated in one horizontal scanning period.

The third row from the top in FIG. 6 shows a read column address that is a column address on which the pixel drive address decoder 112 performs reading (reading operation of pixel charges). The read column address is one for each vertical scanning period of the vertical synchronization signal V from the column address indicating the leftmost pixel column in the column direction of the pixel array unit 111 to the column address indicating the rightmost pixel column. It is incremented (in FIG. 6 is incremented by 1 from the column address m _R).

The fourth from the top in FIG. 6 shows a normal shutter column address which is a column address at which the pixel drive address decoder 112 performs a shutter (a pixel charge sweeping operation). The normal shutter column address is 1 for each vertical scanning period of the vertical synchronization signal V from the column address indicating the leftmost pixel column in the column direction of the pixel array unit 111 to the column address indicating the rightmost pixel column. (In FIG. 6, it is incremented by 1 from the column address m _S ). A normal shutter performed on a pixel column of a predetermined column address m _S is performed at a time before the charge (light) accumulation time (exposure time) from the time when reading is performed. That is, in the example of FIG. 6, in the pixel array section 111, towards the pixel array indicated by the column address m _R than the pixel row indicated by the row address m _S is that on the right.

  The fifth to eighth from the top in FIG. 6 are column addresses at which the pixel drive address decoder 112 performs a shutter (a pixel charge sweeping operation), and a boundary region shutter column that is a column address of the boundary pixel column in the boundary region. The address is shown. The boundary area shutter column address is fixed regardless of the vertical scanning period of the vertical synchronization signal V. As described above, the boundary pixel column forming the boundary region described in FIG. 5 is set by the boundary region shutter column address. Further, the boundary area shutter row address can be arbitrarily set by the user.

In FIG. 6, the column address M _B, the boundary indicates the column address of the first pixel th column of the light-blocking region side from the column address N _E is the column address of the first pixel row th exposure region side from the boundary Show. That is, the boundary pixel column set by the boundary region shutter column address in FIG. 6 includes two pixel columns of the light shielding region and two pixel columns of the exposure region adjacent to the boundary. Note that the number of pixel columns constituting the boundary pixel column is not limited to the example of FIG.

  Here, when it is not necessary to distinguish the normal shutter column address from the boundary area shutter column address, these are collectively referred to as a shutter column address hereinafter.

  The ninth pixel from the top (second from the bottom) in FIG. 6 shows a pixel read signal for instructing the pixel drive address decoder 112 to perform a read (reading operation of a pixel charge). The pixel read signal becomes a high level once every vertical scanning period of the vertical synchronization signal V.

  In other words, the pixel drive address decoder 112 performs reading on the pixel of the read column address that is set at that time once per vertical scanning period. Since the read column address is incremented by 1 for each vertical scanning period of the vertical synchronizing signal V, the pixel drive address decoder 112 reads one column for each vertical scanning period of the vertical synchronizing signal V.

  A pixel shutter signal for instructing the pixel drive address decoder 112 to perform a shutter (a pixel charge sweeping operation) is shown in the tenth from the top (first from the bottom) in FIG. The pixel shutter signal becomes a high level once every vertical scanning period of the vertical synchronization signal V.

  That is, the pixel drive address decoder 112 performs shutter for the pixel of the shutter column address that is set at that time once in each vertical scanning period. Since the normal shutter column address is incremented by 1 for each vertical scanning period of the vertical synchronization signal V, the pixel drive address decoder 112 performs shutter by one column for each vertical scanning period of the vertical synchronization signal V.

  In addition, since the boundary area shutter column address is fixed regardless of the vertical scanning period of the vertical synchronization signal V, the pixel drive address decoder 112 has a boundary that forms a boundary area for each vertical scanning period of the vertical synchronization signal V. Shutter is performed on all the pixels in the pixel column.

  According to the above configuration, the charges of the pixels included in the boundary region between the light shielding region and the exposure region are swept out at a certain interval (for example, one vertical scanning period), so that the charge overflows in the pixels in the exposure region. Even when it is emitted, it is possible to suppress the leakage of charges to the pixels in the light shielding region, that is, blooming. This makes it possible to stably obtain the correct black level reference.

  In the above description, the control unit 114 causes the shutter to be applied to all pixels in the boundary region every vertical scanning period of the vertical synchronization signal V. However, the shutter is applied to the pixels in the boundary region. The time interval to be performed is not limited to this. More specifically, in FIG. 6, the pixel shutter signal is set to the High level once every vertical scanning period of the vertical synchronization signal V, but the present invention is not limited to this, and every pixel is scanned every vertical scanning period. The high level may be set a plurality of times, or the high level may be set once every a plurality of vertical scanning periods. Further, the pixel shutter signal may be divided into a signal for performing shutter for a pixel at a normal shutter column address and a signal for performing shutter for a pixel at a boundary region shutter column address.

  In the above description, the read column address is incremented by 1 from the column address indicating the leftmost pixel column in the column direction of the pixel array unit 111 to the column address indicating the rightmost pixel column. All pixels in the pixel array unit 111 are read out. However, in the boundary region, for example, since a shutter is performed every vertical scanning period, sufficient charge is not accumulated in the pixels included in the exposure region of the boundary region. Therefore, the boundary pixel column forming the boundary region may not be read.

  In the above description, the image sensor has been described as including either a pixel drive address decoder that performs reading and shuttering in units of rows or a pixel driving address decoder that performs reading and shuttering in units of columns. A pixel drive address decoder may be provided.

  The embodiments of the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

  11 pixel array unit, 12 pixel drive address decoder, 13 horizontal selection circuit, 14 control unit, 111 pixel array unit, 112 pixel drive address decoder, 113 vertical selection circuit, 114 control unit

Claims (4)

In a rolling shutter type image sensor, in which pixels are two-dimensionally arranged in a vertical direction and a horizontal direction, and have a pixel array unit including an exposure region and a light shielding region,
In the pixel array unit, an address is set for a pixel column that is arranged in parallel with a boundary between the exposure region and the light shielding region, and is a plurality of the pixel columns including the boundary. An image sensor comprising control means for causing the boundary pixel column to perform a shutter at a predetermined time interval. The image sensor according to claim 1, wherein the control unit causes the boundary pixel column to which an address is set to perform a shutter for each scanning period of a pixel column arranged in parallel with the boundary. The image sensor according to claim 1, wherein the boundary pixel column is a predetermined number of pixel columns arranged on the light shielding region side from the boundary. The image sensor according to claim 1, wherein the boundary is formed in a vertical direction or a horizontal direction in the pixel array unit.

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