JP2017055330A - Solid-state imaging device and camera system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state imaging device and camera system that are capable of detecting light with high sensitivity and make it possible to reduce occurrence of output saturation.SOLUTION: A solid-state imaging device according to an embodiment comprises a pixel area and a driving circuit. The pixel area comprises a unit arrangement of pixels. A pixel includes a photoelectric conversion element. The driving circuit supplies a driving signal to the pixel. The driving signal is a signal for reading a signal charge generated at the photoelectric conversion element. The unit arrangement comprises a first pixel and a second pixel. The first pixel, W pixel, is a pixel having the highest light sensitivity of pixels in the unit arrangement. The second pixel is a pixel other than the first pixel. The driving circuit supplies the driving signal to the first pixel and second pixel when a first time, time T1, has passed after start of storing signal charges at the first and second pixels and when a second time, time T2 has passed.SELECTED DRAWING: Figure 5

Description

  The present embodiment relates to a solid-state imaging device and a camera system.

  A pixel array for detecting light with high sensitivity has been proposed for a solid-state imaging device. The solid-state imaging device is desired to reduce the occurrence of output saturation due to the signal charge accumulated in the pixel reaching the saturation charge amount.

JP 2009-268072 A

  An object of one embodiment is to provide a solid-state imaging device and a camera system that can detect light with high sensitivity and can reduce the occurrence of output saturation.

  According to one embodiment, the solid-state imaging device includes a pixel region and a drive circuit. The pixel area includes a unit array of pixels. The pixel includes a photoelectric conversion element. The drive circuit supplies a drive signal to the pixel. The drive signal is a signal for reading the signal charge generated by the photoelectric conversion element. The unit array includes a first pixel and a second pixel. The first pixel is a pixel having the highest light sensitivity among the pixels in the unit array. The second pixel is a pixel other than the first pixel. The drive circuit supplies a drive signal to the first pixel and the second pixel when the first time has elapsed and the second time has elapsed since the start of signal charge accumulation in the first pixel and the second pixel. . The second time is a frame rate period of the camera system including the solid-state imaging device.

FIG. 1 is a block diagram of the solid-state imaging device according to the first embodiment. FIG. 2 is a block diagram of a camera system including the solid-state imaging device shown in FIG. FIG. 3 is a schematic diagram of a unit array provided in the pixel region shown in FIG. FIG. 4 is a diagram showing the relationship between the exposure time in the pixel of the unit array shown in FIG. 3 and the number of electrons accumulated in the pixel. FIG. 5 is a diagram showing the relationship between the exposure time in the pixel of the unit array shown in FIG. 3 and the number of electrons accumulated in the pixel. FIG. 6 is a diagram for explaining frame synthesis in the camera system shown in FIG. FIG. 7 is a diagram showing a first modification of the unit array provided in the pixel region shown in FIG. FIG. 8 is a diagram showing a second modification of the unit array provided in the pixel region shown in FIG. FIG. 9 is a diagram illustrating frame composition in the camera system of the second embodiment.

  Hereinafter, a solid-state imaging device and a camera system according to embodiments will be described in detail with reference to the drawings. Note that the present invention is not limited to these embodiments.

(First embodiment)
FIG. 1 is a block diagram of the solid-state imaging device according to the first embodiment. FIG. 2 is a block diagram of a camera system including the solid-state imaging device shown in FIG. The camera system 1 is an electronic device including the camera module 2 and is, for example, a mobile terminal with a camera. The camera system 1 may be an electronic device such as a digital camera or an in-vehicle camera.

  The camera system 1 includes a camera module 2 and a post-processing unit 3. The camera module 2 includes an imaging optical system 4 and a solid-state imaging device 5. The post-processing unit 3 includes an image signal processor (ISP) 6, a recording unit 7, and a display unit 8.

  The imaging optical system 4 captures light from the subject. The imaging optical system 4 includes an imaging lens (not shown) that forms a subject image. The solid-state imaging device 5 captures a subject image. The solid-state imaging device 5 is a CMOS (Complementary Metal Oxide Semiconductor) image sensor. The solid-state imaging device 5 may be a CCD (Charge Coupled Device).

  The ISP 6 performs signal processing on the image signal from the solid-state imaging device 5. The ISP 6 performs various signal processing such as demosaic processing, white balance adjustment, color matrix processing, and gamma correction. The recording unit 7 records an image that has undergone signal processing in the ISP 6 on a storage medium or the like. The recording unit 7 outputs an image signal to the display unit 8 according to a user operation or the like.

  The display unit 8 displays an image according to the image signal from the ISP 6 or the image signal read from the recording unit 7. The display unit 8 is, for example, a liquid crystal display. The camera system 1 performs feedback control of the camera module 2 based on data that has undergone signal processing in the ISP 6.

  The solid-state imaging device 5 includes a pixel region 11, a control circuit 12, a row scanning circuit 13, a column scanning circuit 14, a column processing circuit 15, and an imaging processing circuit 16. The pixel area 11 is an area where pixel unit arrays are arranged in a matrix. The pixel includes a photodiode that is a photoelectric conversion element. The photoelectric conversion element generates a signal charge corresponding to the amount of incident light. The pixel accumulates signal charges generated according to the amount of incident light.

  The control circuit 12, the row scanning circuit 13, the column scanning circuit 14, the column processing circuit 15 and the imaging processing circuit 16 constitute a peripheral circuit unit integrated on a chip on which the pixel region 11 is mounted. Various data and clock signals for driving the solid-state imaging device 5 are supplied from the ISP 6 outside the chip to the control circuit 12 via the imaging processing circuit 16.

  The control circuit 12 generates various pulse signals for controlling the driving of the peripheral circuit unit according to the clock signal. The control circuit 12 supplies a pulse signal instructing drive timing to each of the row scanning circuit 13, the column scanning circuit 14, the column processing circuit 15, and the imaging processing circuit 16.

  The row scanning circuit 13 serving as a drive circuit supplies a drive signal for reading out signal charges generated by the photoelectric conversion elements to the pixels in the pixel region 11. The row scanning circuit 13 includes a shift register and an address decoder.

  The control circuit 12 supplies a pulse signal corresponding to the vertical synchronization signal to the row scanning circuit 13. The row scanning circuit 13 sequentially selects pixel rows from which pixel signals are read according to the pulse signal from the control circuit 12. The row scanning circuit 13 performs readout scanning by sequentially supplying a readout signal for each pixel in the selected pixel row. The read signal is a drive signal for reading a pixel signal generated according to the amount of incident light from the pixel.

  The row scanning circuit 13 performs sweep-out scanning by supplying a reset signal to each pixel prior to supplying a readout signal to each pixel. The reset signal is a drive signal for discharging the charge remaining in the photoelectric conversion element. Each pixel accumulates signal charges generated according to the amount of incident light from when the reset signal is supplied to when the readout signal is supplied.

  The drive signal is transmitted from the row scanning circuit 13 to each pixel through the pixel drive line 18. The pixel drive line 18 is provided for each pixel row in the pixel region 11. A pixel row consists of pixels arranged in the row direction (horizontal direction).

  The pixel signal is transmitted from each pixel to the column processing circuit 15 through the vertical signal line 19. The vertical signal line 19 is provided for each pixel column in the pixel region 11. The pixel column is composed of pixels arranged in the column direction (vertical direction). The column processing circuit 15 processes the pixel signal transmitted through the vertical signal line 19 by a unit circuit (not shown) provided for each pixel column.

  The column processing circuit 15 performs correlated double sampling processing (CDS) for reducing fixed pattern noise on the pixel signal. The column processing circuit 15 performs AD conversion, which is conversion to a digital signal, on the pixel signal, which is an analog signal. The column processing circuit 15 may perform processing other than CDS and AD conversion. The column processing circuit 15 holds the pixel signal that has undergone CDS and AD conversion for each unit circuit.

  The column scanning circuit 14 includes a shift register and an address decoder. The control circuit 12 supplies a pulse signal corresponding to the horizontal synchronization signal to the column scanning circuit 14. The column scanning circuit 14 sequentially selects pixel columns from which pixel signals are read according to the pulse signal from the control circuit 12. The column processing circuit 15 sequentially outputs signals held in each unit circuit in accordance with the selective scanning by the column scanning circuit 14.

  The imaging processing circuit 16 is a processing circuit that processes an image signal including the signal from the column processing circuit 15 as a component. The imaging processing circuit 16 performs various signal processing such as scratch correction, noise reduction, shading correction, white balance adjustment, and high dynamic range (HDR) synthesis.

  The solid-state imaging device 5 outputs an image signal that has been processed by the imaging processing circuit 16 to the outside of the chip. The camera system 1 may perform signal processing performed in the solid-state imaging device 5 in the present embodiment in a circuit other than the peripheral circuit unit on the same chip as the pixel region 11. The signal processing may be performed by the ISP 6 of the post-processing unit 3 instead of the peripheral circuit unit. The camera system 1 may perform signal processing performed in the peripheral circuit unit in both the peripheral circuit unit and the ISP 6. The peripheral circuit unit and the ISP 6 may perform signal processing other than the signal processing described in the present embodiment.

  FIG. 3 is a schematic diagram of a unit array provided in the pixel region shown in FIG. The unit array includes four pixels. The four pixels form a matrix of two in the row direction and two in the column direction. The four pixels in the unit array are a W pixel, an R pixel, a B pixel, and a G pixel.

  The W pixel is a pixel that detects white light. White light includes light having a wavelength in the entire visible region. The W pixel includes a transparent filter (not shown) that transmits white light. The R pixel is a pixel that detects red light. The R pixel includes a color filter (not shown) that selectively transmits red light.

  The G pixel is a pixel that detects green light. The G pixel includes a color filter (not shown) that selectively transmits green light. The B pixel is a pixel that detects blue light. The B pixel includes a color filter (not shown) that selectively transmits blue light.

  The W pixel detects light in a wider wavelength range than the R pixel, G pixel, and B pixel. The W pixel is the first pixel having the highest light sensitivity among the pixels in the unit array. The R pixel, the G pixel, and the B pixel are second pixels other than the first pixel.

  The R pixel and the B pixel are arranged diagonally opposite to each other in the unit array. The W pixel and the G pixel are arranged diagonally opposite to each other in the unit array. In the unit array, one G pixel in the Bayer array is replaced with a W pixel.

  4 and 5 are diagrams showing the relationship between the exposure time in the pixel of the unit array shown in FIG. 3 and the number of electrons accumulated in the pixel. 4 and 5, the horizontal axis represents the time from when the reset signal is supplied to the pixel. The origin of the horizontal axis represents the start timing of exposure time when signal charge accumulation is started in the pixel. The vertical axis represents the number of electrons accumulated in the pixel. Each solid line of W, G, R, and B is a graph representing the relationship between the exposure time and the number of electrons in the W pixel, G pixel, R pixel, and B pixel, respectively.

  After the exposure time is started, the number of electrons increases according to the photosensitivity of each pixel. The W pixel having the highest photosensitivity has the highest number of electrons accumulated in the pixel. When the signal charge accumulated in the pixel reaches a saturation charge amount, the output pixel signal is in a saturated state where the level of the output pixel signal is constant. Time T1 is the time from the start of exposure until the signal charge of the W pixel reaches the saturation charge amount.

  FIG. 4 shows the relationship between the exposure time and the number of electrons when the control circuit 12 performs the first control. The row scanning circuit 13 supplies a read signal to the W pixel, the G pixel, the R pixel, and the B pixel by the first control when the time T2 has elapsed since the reset signal was supplied. Time T2 is a frame rate period of the camera system 1.

  From the W pixel, the G pixel, the R pixel, and the B pixel, the signal charges accumulated until the time T2 elapses from the start of exposure are read according to the read signal. The W pixel, G pixel, R pixel, and B pixel output pixel signals corresponding to the signal charges. The solid-state imaging device 5 generates one frame with the time T2 as the exposure time. In such a frame, pixel signals corresponding to the amount of incident light are obtained at the G pixel, R pixel, and B pixel, while output saturation occurs at the W pixel. The camera system 1 records an image acquired every time T2.

  FIG. 5 shows the relationship between the exposure time and the number of electrons when the control circuit 12 performs the second control. The row scanning circuit 13 supplies a first readout signal to each of the W pixel, the G pixel, the R pixel, and the B pixel by the second control when the time T1 has elapsed from the start of exposure. When the time has elapsed, a second read signal is supplied.

  From the W pixel, the G pixel, the R pixel, and the B pixel, the signal charges accumulated until the time T1 elapses from the start of exposure are read according to the first readout signal. The W pixel, the G pixel, the R pixel, and the B pixel output a first pixel signal corresponding to the signal charge.

  The row scanning circuit 13 supplies a reset signal to the W pixel, the G pixel, the R pixel, and the B pixel immediately after the supply of the first readout signal. The W pixel, the G pixel, the R pixel, and the B pixel accumulate signal charges again after the reset signal is supplied.

  From the W pixel, the G pixel, the R pixel, and the B pixel, the signal charges accumulated until the time T2-T1 elapses are read according to the second read signal. The W pixel, the G pixel, the R pixel, and the B pixel output a second pixel signal corresponding to the signal charge.

  The solid-state imaging device 5 generates a first frame having an exposure time of time T1 and a second frame having an exposure time of time T2-T1. The first frame is a first image based on the first pixel signal. The second frame is a second image based on the second pixel signal. In both the first frame and the second frame, a pixel signal corresponding to the amount of incident light is obtained from the W pixel, G pixel, R pixel, and B pixel. The camera system 1 combines the first frame and the second frame, and records an image acquired at every time T2.

  The solid-state imaging device 5 reads pixel signals simultaneously from two pixels arranged in the row direction in the unit arrangement. The solid-state imaging device 5 does not require a configuration for supplying read signals to the pixels in the unit array at different timings. In the solid-state imaging device 5, one pixel drive line 18 is arranged for each pixel row. The solid-state imaging device 5 can have a simple configuration as compared with the case where a plurality of pixel drive lines 18 are required for each pixel row.

  FIG. 6 is a diagram for explaining frame synthesis in the camera system shown in FIG. FIG. 6 shows elements of the imaging processing circuit 16 and the ISP 6 that perform processing for frame synthesis.

  The imaging processing circuit 16 includes a movement amount detection unit 21. The movement amount detection unit 21 detects the movement amount of the camera system 1 in a two-dimensional direction perpendicular to the optical axis of the imaging optical system 4. Such a two-dimensional direction is parallel to the row direction and the column direction of the pixel region 11. The movement amount detection unit 21 detects the movement amount and movement direction of the camera system 1 based on a signal from a sensor (not shown). The sensor is, for example, an angular velocity sensor including a vibration gyro mechanism. The sensor may include a Hall element. The Hall element converts a magnetic field into an electric signal using the Hall effect.

  The movement amount detection unit 21 is not limited to one that detects the movement amount based on a signal from the sensor. The movement amount detection unit 21 may detect the movement amount between the first frame and the second frame by image detection processing.

  The imaging processing circuit 16 sends the RAW image signal (RAW1) of the first frame, the RAW image signal (RAW2) of the second frame, and the movement amount data detected by the movement amount detection unit 21 to the ISP 6. The ISP 6 includes a position adjustment unit 22 and an image composition unit 23.

  The position adjustment unit 22 adjusts the cutout range of the first frame and the second frame according to the movement amount data. The position adjustment unit 22 aligns the subject images of the first frame and the second frame. The image synthesis unit 23 synthesizes the first frame and the second frame that have undergone the adjustment by the position adjustment unit 22. The camera system 1 can obtain an image with reduced blur by synthesizing the first frame and the second frame that are aligned with each other.

  The solid-state imaging device 5 performs switching from the first control to the second control when, for example, output saturation at the W pixel is detected. The solid-state imaging device 5 may perform the second control when it is determined that the shooting is performed in a high illumination environment. The solid-state imaging device 5 determines whether it is a high illuminance environment according to the analog gain or the illuminance detection result. The solid-state imaging device 5 may switch between the first control and the second control according to the designation of the shooting mode by the user.

  The time T1 is not limited to the time required from the start of exposure until the signal charge of the W pixel reaches the saturation charge amount. The time T1 may be shorter than the time required for the signal charge of the W pixel to reach the saturation charge amount. In order to secure the time T2-T1 such that the frame rate of the second frame does not exceed the fastest frame rate that the solid-state imaging device 5 can drive, the solid-state imaging device 5 may adjust the length of the time T1. good.

  In order to obtain an appropriate frame rate, the solid-state imaging device 5 may take measures such that the W pixel and other pixels, for example, the G pixel have an appropriate sensitivity difference. For example, the sensitivity difference between the W pixel and the G pixel is such that the time until the signal charge of the W pixel reaches the saturation charge amount is about half of the time until the signal charge of the G pixel reaches the saturation charge amount. Adjusted. The sensitivity difference may be adjusted by any method. For example, the sensitivity difference may be adjusted by selecting a material for the color filter pigment.

  The time T1 may be a time set in advance by predicting the time until the signal charge of the W pixel reaches the saturation charge amount. The time T1 may be a fixed time that is half the time T2. When the frame rate of the camera system 1 is 30 fps (frames per second), T1 is set to 1/60 second. The frame rate period T2 of the camera system 1 is set to 1/30 second.

  The solid-state imaging device 5 reads out the pixel signal of the W pixel when the time T1 has elapsed and when the time T2 has elapsed, thereby reducing the occurrence of output saturation of the W pixel. The solid-state imaging device 5 reads out the pixel signals of the R pixel, the G pixel, and the B pixel at the elapse of the time T1 and at the elapse of the time T2, thereby reducing the sensitivity of the R pixel, the G pixel, and the B pixel with respect to the W pixel. I can make up for it. The solid-state imaging device 5 can detect R light, G light, and B light with high sensitivity. The camera system 1 can reduce the generation of color noise by highly sensitive detection of R light, G light, and B light.

  FIG. 7 is a diagram showing a first modification of the unit array provided in the pixel region shown in FIG. The four pixels in the unit array are two W pixels that are first pixels, and R and B pixels that are second pixels. In the first modification, the G pixel in the unit array shown in FIG. 3 is replaced with a W pixel. Also in the case of the first modification, the solid-state imaging device 5 can reduce the occurrence of output saturation of the W pixel and can detect R light and B light with high sensitivity.

  FIG. 8 is a diagram showing a second modification of the unit array provided in the pixel region shown in FIG. The unit array of the second modification is a Bayer array. The four pixels are two G pixels, an R pixel, and a B pixel.

  The G pixel detects light in a wider wavelength range than the R pixel and the B pixel. The G pixel is the first pixel having the highest light sensitivity among the pixels in the unit array. The R pixel and the B pixel are second pixels. The time T1 is, for example, the time from the start of exposure until the signal charge of the G pixel reaches the saturation charge amount. In the case of the second modification, the solid-state imaging device 5 can reduce the occurrence of output saturation of the G pixel and can detect R light and B light with high sensitivity.

  According to the first embodiment, the solid-state imaging device 5 reduces the occurrence of output saturation of the first pixel by reading the pixel signal of the first pixel when the first time elapses and when the second time elapses. Let The solid-state imaging device 5 can sufficiently compensate for the lack of sensitivity of the second pixel with respect to the first pixel by reading the pixel signal of the second pixel when the first time elapses and when the second time elapses. Thereby, the solid-state imaging device 5 can acquire the effect that it can detect light with high sensitivity and can reduce generation | occurrence | production of output saturation.

(Second Embodiment)
FIG. 9 is a diagram illustrating frame composition in the camera system of the second embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals, and repeated description will be omitted as appropriate. FIG. 9 shows elements of the imaging processing circuit 16 and the ISP 6 that perform processing for frame synthesis.

  The imaging processing circuit 16 includes a movement amount detection unit 21, a position adjustment unit 22, and an image composition unit 23. The movement amount detection unit 21 detects the movement amount of the camera system 1. The position adjustment unit 22 adjusts the cutout range of the first frame and the second frame according to the movement amount data. The image synthesis unit 23 synthesizes the first frame and the second frame that have undergone the adjustment by the position adjustment unit 22. The imaging processing circuit 16 sends a RAW image signal of an image obtained by combining the first frame and the second frame to the ISP 6.

  Also in the second embodiment, the camera system 1 can obtain an image with reduced blur by synthesizing the first frame and the second frame that are aligned with each other.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 Camera system, 5 Solid-state imaging device, 6 ISP, 11 pixel area | region, 13 row scanning circuit, 16 Imaging processing circuit, 21 Movement amount detection part, 22 Position adjustment part, 23 Image composition part

Claims (8)

A pixel region comprising a unit array of pixels including a photoelectric conversion element;
A solid-state imaging device comprising: a drive circuit that supplies a drive signal for reading signal charges generated by the photoelectric conversion element to the pixel;
The unit array includes a first pixel having the highest light sensitivity among the pixels in the unit array, and a second pixel other than the first pixel,
The drive circuit includes a second time that is a frame rate period of a camera system including the solid-state imaging device when a first time has elapsed from the start of signal charge accumulation in the first pixel and the second pixel. A solid-state imaging device that supplies the drive signal to the first pixel and the second pixel when the time has elapsed.   2. The solid-state imaging device according to claim 1, wherein the first time is a time until a signal charge accumulated in the first pixel reaches a saturation charge amount.   The solid-state imaging device according to claim 1, wherein the first time is a preset time.   A first image based on a first pixel signal read from the first pixel and the second pixel in response to the drive signal supplied when the first time has elapsed, and when the second time has elapsed An image composition unit for synthesizing the second image based on the second pixel signal read from the first pixel and the second pixel in accordance with the drive signal supplied to the first pixel. The solid-state imaging device according to any one of 3. A movement amount detection unit for detecting the movement amount of the solid-state imaging device;
The solid-state imaging device according to claim 4, wherein the image synthesis unit synthesizes the first image and the second image that are aligned according to the movement amount.   6. The solid-state imaging device according to claim 1, wherein the first pixel detects white light including light having a wavelength in the entire visible region.   The solid-state imaging device according to claim 1, wherein the first pixel detects green light. A pixel region comprising a unit array of pixels including a photoelectric conversion element;
A drive circuit for supplying a drive signal for reading out the signal charge generated by the photoelectric conversion element to the pixel;
A processor system for processing a signal from the pixel region,
The unit array includes a first pixel having the highest light sensitivity among the pixels in the unit array, and a second pixel other than the first pixel,
When the first time has elapsed from the start of signal charge accumulation in the first pixel and the second pixel, and when the second time that is the frame rate period of the camera system has elapsed, Supplying the drive signal to the first pixel and the second pixel;
The processor includes a first image based on a first pixel signal read from the first pixel and the second pixel according to the drive signal supplied when the first time has elapsed, and the second time. An image composition unit configured to synthesize the second image based on the second pixel signal read from the first pixel and the second pixel in accordance with the drive signal supplied when the time elapses. Camera system.

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