JP2007135073A - Solid state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make exposure times about all pixels to be constant, and set to a desired frame rate even when not using a mechanical shutter in an X-Y address type imaging element having only a rolling electronic shutter function as an electronic shutter. <P>SOLUTION: Exposure times about all pixels are to be controlled so as to be the same by setting an image signal period and a blank image signal period (VBLK) in which the image signal is not to be outputted from a solid state imaging element to have integral multiplication of a horizontal scanning period. The desired frame rate can be obtained by adjusting length of all horizontal scanning periods. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device having a photoelectric conversion element, and more particularly to a solid-state imaging device using a CMOS image sensor and having a feature in a driving method.

  When driving solid-state image sensors such as CCD (Charge Coupled Device) image sensors and XY address-type image sensors represented by CMOS (Complementary Metal-Oxide-Semiconductor) image sensors, various drives such as vertical transfer pulses and horizontal transfer pulses A signal is used. These drive signals are generated in a timing generator for driving the solid-state imaging device. Such a timing generator generally drives an image pickup apparatus so as to satisfy a broadcast format signal format such as NTSC (National Television System Committee) or PAL (Phase Alternating by Line).

  For example, as shown in FIG. 6, an effective pixel region 601 in which information of each pixel is derived as a video signal, and an optical black (optical black) region 602 arranged in a state of being shielded from the upper, lower, left, and right sides of the effective pixel region. 7 is driven from a timing generator and is sequentially applied to the solid-state imaging device. For example, the horizontal transfer pulses φH1 and φH2 are generated at a driving frequency of about 12.27 MHz, and the horizontal synchronization pulse HD and the vertical synchronization pulse VD are set at a predetermined clock count (eg 780) and row count (eg 525). Exit. Accordingly, the timing generator can obtain a video signal of 30 frames / second (hereinafter referred to as “FPS”) from the solid-state imaging device.

  As described above, in order to realize the frame rate of the video signal to a value satisfying a broadcast format signal format such as 30 FPS or 60 FPS, a method of changing the drive frequency is conceivable. However, the driving frequency is determined as a frequency that can be realized, and there is a risk that a large amount of electromagnetic waves is generated at a high frequency.

  It is also possible to configure a field memory with a storage device such as DRAM (Dynamic Random Access Memory) and perform frame thinning on the video signal obtained by the solid-state imaging device. In this case, the storage device such as DRAM Since it is necessary to additionally mount the device, the device configuration becomes complicated, and processing for controlling the storage device is required, leading to an increase in product cost.

Therefore, in Japanese Patent Laid-Open No. 2001-008113, a predetermined unit of video signal obtained from a solid-state image sensor includes a scanning period and a blanking period from the start of output to the end of output. In a driving method of a solid-state imaging device that provides a driving signal, an empty video signal engine that does not output a video signal from the solid-state imaging device for at least one of the horizontal direction and the vertical direction of the solid-state imaging device for each predetermined unit of video signal By adding, it is possible to set the frame rate to a desired value.
Japanese Patent Laid-Open No. 2001-008113

  However, in the XY address type image pickup device using the rolling electronic shutter, when the exposure time control in the mode not using the mechanical shutter is performed by the above method, for example, as shown in FIG. A horizontal scanning period X having a different length from the scanning period is added. Since the exposure time is controlled by the interval of the horizontal scanning period, there is a problem that the exposure time varies between the lines before the nth line including the horizontal scanning period X in the exposure period and the lines after the n + 1st line not including the horizontal scanning period X. Will occur.

  Therefore, in the present invention, in the XY address type solid-state imaging device, the solid-state imaging device is driven so that a predetermined unit of video signal obtained from the solid-state imaging device includes a scanning period and a blanking period from the output start to the output end. In a solid-state imaging device that gives a signal and performs exposure time control so that the exposure start time and the readout start time are different in the row direction or the column direction of the video signal, the video signal period and the video signal from the solid-state image sensor are not output A desired frame rate is realized by setting the sky video signal period to be an integral multiple of the horizontal scanning period or by adjusting the length of all horizontal scanning periods. Furthermore, after setting the video signal period and the empty video signal period in which the video signal from the solid-state imaging device is not output to be an integral multiple of the horizontal scanning period, the lengths of all the horizontal scanning periods are adjusted in order. .

  As described above, by using the method according to claim 1, in the XY address type image pickup device using the rolling electronic shutter, even if the exposure time control is performed without using the mechanical shutter, exposure of all rows is performed. Time can be kept constant. Also, by using the method according to claim 2 and the method according to claim 3, it is possible to set the desired frame rate with high accuracy. In addition, by using the method according to claims 4, 5, and 6, in a situation where image distortion is conspicuous, by using a frame rate setting method in which image distortion is less likely to occur, imaging with less image distortion is possible. The driving of the device can be realized. When the mechanical shutter is used, the method of claim 7 is used, and when the mechanical shutter is not used, the method of claim 1 or 2 is used to keep the exposure time of all rows constant. In addition, a solid-state imaging device with less image distortion can be realized.

  An embodiment of the present invention will be described with reference to FIGS.

FIG. 2 shows the configuration of an image sensor that employs an XY address type scanning method.
In FIG. 2, 201 is a unit pixel, 202 is a photodiode (PD), 203 is a transfer switch, 204 is a floating diffusion (FD), 205 is an amplification MOS amplifier that functions as a source follower, 206 is a selection switch, and 207 is reset. A switch, 208 is a signal line, 209 is a constant current source serving as a load of the amplification MOS amplifier 205, 210 is a selection switch, 211 is an output amplifier, 212 is a vertical scanning circuit, 213 is a readout circuit, and 214 is a horizontal scanning circuit. In FIG. 2, for simplification of the drawing, only the pixel unit 201 is shown as 4 rows × 4 columns, but actually, a very large number of pixel units 201 are two-dimensionally arranged.

  The unit pixel 201 includes a PD 202, a transfer switch 203, an FD 204, an amplification MOS amplifier 205, a selection switch 206, and a reset switch 207. Light is converted into electric charge in the PD 202, and the electric charge generated in the PD 202 is transferred with the transfer pulse φTX by the transfer switch 203 and temporarily stored in the FD 204. The FD 204, the amplification MOS amplifier 205, and the constant current source 209 constitute a floating diffusion amplifier. The signal charge of the pixel selected by the selection switch 206 is converted into a voltage by the selection pulse φSEL, and the readout circuit 213 passes through the signal output line 208. Is output. Further, a signal to be output is selected by the selection switch 210 driven by the horizontal scanning circuit 214, and is output to the outside of the image sensor through the output amplifier 211. The charge accumulated in the FD 204 is removed by the set switch 207 by a reset pulse φRES. In the vertical scanning circuit 212, the transfer switch 203, the selection switch 206, and the reset switch 207 are selected.

  For each of the pulse signals φTX, φRES, and φSEL, pulse signals that are selected by the vertical scanning circuit 212 and applied to, for example, the nth scanning row are described as φTXn, φRESn, and φSELn.

  FIG. 3 shows a part of the color filter array used in the solid-state imaging device of FIG. A case is shown in which the first color filter is red (R), the second color filter is green (G), the third color filter is green (G), and the fourth color filter is blue (B). . This array of color filter arrays is called a Bayer array, among the primary color filter arrays, and is a color filter array having high resolution and excellent color reproducibility.

  FIG. 4 shows a system outline of an image pickup apparatus using the image pickup element of FIG. In FIG. 4, 401 is a lens unit (denoted as a lens), 402 is a lens driving unit, 403 is a mechanical shutter (denoted as mechanical shutter), 404 is a mechanical shutter driving unit (denoted as shutter driving unit), and 405 is shown in FIG. 406 is an imaging signal processing circuit, 407 is a timing generation unit, 408 is a memory unit, 409 is an overall control calculation unit, 410 is a recording medium control interface unit (recorded as a recording medium control I / F unit), Reference numeral 411 denotes a recording medium, 412 denotes an external interface unit (noted as an external I / F unit), 413 denotes a photometric unit, and 414 denotes a distance measuring unit.

  The subject image that has passed through the lens unit 401 is formed on the image sensor 405. The subject image coupled to the image sensor 405 is captured as an image signal, and the image signal processing circuit 406 performs image signal amplification, A / D conversion for converting an analog signal to a digital signal, and an image after A / D conversion. Various corrections and compression of image data are performed on the data.

  The lens unit 401 is driven and controlled by a lens driving unit 402 such as zoom, focus, and diaphragm. The shutter 403 is a shutter mechanism having only a curtain corresponding to the rear curtain of a focal plane type shutter used in a single-lens reflex camera, and is driven and controlled by a shutter drive unit 404. The timing generation unit 407 outputs various timing signals to the image sensor 405 and the image signal processing circuit 406. The overall control calculation unit 409 controls the entire imaging apparatus and performs various calculations. The memory 408 temporarily stores the image data, and the recording medium control interface unit 410 records or reads the image data on the recording medium. The recording medium 411 is a detachable storage medium such as a semiconductor memory, and records or reads image data. The external interface unit 412 is an interface for communicating with an external computer or the like. The photometry unit 413 detects the brightness information of the subject, and the distance measurement unit 414 detects the distance information to the subject.

  Next, an exposure time control sequence in the individual image sensor of the present invention will be described with reference to FIGS.

  FIG. 5 shows a drive pulse and an operation sequence in the rolling electronic shutter operation. In FIG. 5, for simplicity of description, the drive control for four rows from n rows to n + 3 rows selected by the vertical scanning circuit 212 will be described.

  In the n-th row, first, φRESn and φTXn are applied during a period from time t51 to t52, the transfer switch 203 and the reset switch 207 are turned on, and a reset operation for removing unnecessary charges accumulated in the PD 202 and the FD 204 in the n-th row. I do. At time t52, the transfer switch 203 is turned off, and an accumulation operation for accumulating the photocharge generated in the PD 202 is started. Next, at time t <b> 54, φTXn is applied to turn on the transfer switch 203, and a transfer operation for transferring the photocharge accumulated in the PD 202 to the FD 204 is performed. The reset switch 207 needs to be turned off prior to the transfer operation. In the drive control shown in FIG. 7, the reset switch 207 is turned off simultaneously with the transfer switch 203 at time t52. Here, the accumulation time is from time t52 when the reset operation ends to time t55 when the transfer starts.

  After the transfer operation of the n-th row is completed, φSELn is applied to turn on the selection switch 206, whereby the charge held in the FD 204 is converted into a voltage and output to the reading circuit 213. The signals temporarily held in the reading circuit 213 are sequentially output from the time t56 by the horizontal scanning circuit 212. The time from the start of transfer at time t54 to the end of reading at time t57 is T3read, and the time from time t51 to time t53 is T3wait.

  Similarly, in other rows, the time from the start of transfer to the end of reading is T3read, and the time from the start of resetting of one row to the start of resetting of the next row is T3wait.

  FIG. 1 shows a relationship between an exposure period of each row constituting an imaging region on an image sensor and a horizontal scanning period and a vertical scanning period synchronized by a horizontal synchronizing pulse and a vertical synchronizing pulse in a driving method of an imaging apparatus according to the present invention. Show. The reset operation period, the read operation period, and the transfer operation period are omitted. As shown in FIG. 1, all horizontal scanning periods are the same period.

  When the number of horizontal scanning periods included in one vertical scanning period is X and the number of reference clocks included in one horizontal scanning period is Y, X and Y are set as follows.

X = (number of vertical scanning pixels) + (number of horizontal scanning periods in the vertical blanking period) + α (Expression 1)
Y = (the number of horizontal reading pixels) + (the number of reference clocks in the horizontal blanking period) + (the number of reference clocks required for skipping rows) + β (Expression 2)
However, α is an integer multiple of the horizontal scanning period.

  Here, the frame rate of the driving mode is obtained by the following equation when the frequency (Hz) of the reference clock is Z.

(Frame rate) = Z / (X · Y) (Formula 3)
For this reason, the frame rate can be set to the designer's desired value regardless of the method of “setting only the α value”, “setting only the β value”, or “setting both the α and β values”. Can be set to In the XY address type image pickup device using a rolling electronic shutter as in the present invention, as described with reference to FIG. 5, the exposure period is between a reset operation and a read operation for removing unnecessary charges accumulated in the PD 202. However, since all the horizontal scanning periods are the same, the exposure times of some rows constituting the imaging region are different as shown in FIG. The exposure time of all the imaging areas can be made uniform.

  On the other hand, when the frame rate is set by the above method, the period that can be adjusted by α is longer than the period that can be adjusted by β. Therefore, in order to set the desired exposure time with high accuracy, α It is better to set β after setting.

  Incidentally, the rolling electronic shutter operation shown in FIG. 5 has a problem that the accumulation time differs between the upper part and the lower part of the screen by the time required for scanning the screen. This is because the time T3wait from the reset and transfer scan of a certain row to the reset and transfer scan of the next row needs to be longer than the time T3read from the start of transfer to the end of reading. In particular, when the number of pixels is large, the difference in accumulation time between the upper and lower portions of the screen becomes large. The difference in accumulation time between the upper and lower parts of the screen is when the relative speed between the subject and the imaging device is high, or when the exposure time is short, the time required for reading and transferring with an image sensor using a high-pixel image sensor. Depending on the shooting environment, such as when the subject is long, the subject appears distorted.

  The accumulation time shift for each row must be equal to or greater than T3read. Since T3read corresponds to one horizontal scanning period, the horizontal scanning period may be shortened to reduce the accumulation time shift. That is, Y may be reduced. Among the elements constituting Y, the number of horizontal reading pixels, the number of reference clocks in the horizontal blanking period, and the number of reference clocks required for skipping rows are predetermined by the system components, so β is set as small as possible. Just do it.

  For example, the number of vertical reading pixels is 524, the number of horizontal scanning periods in the vertical blanking period is 200, the number of horizontal reading pixels is 437, the number of reference clocks in the horizontal blanking period is 400, and the reference clock required for skipping rows In an imaging apparatus in which the number of is 16 and the reference clock frequency of the driving mode is 40 MHz, when 60 FPS is realized, α is set as a value that sets α as large as possible and β as small as possible. Is 25 and β is 37, thereby realizing 60.005FPS.

  Alternatively, α is set to 58 and β is set to 0 as a setting for making the distortion of the subject smaller than in the above example. This is 59.966 FPS, which is slightly insufficient for the desired 60 FPS, but compared to the case where α is 25 and β is 37, the difference in exposure time between the first read line and the last read line in one frame is 0.48. msec can be relaxed. Then, the overall control calculation unit 409 measures the position of the subject between frames, and determines that there is no moving subject if the difference between frames is zero or less than a predetermined value. If the difference is greater than or equal to a predetermined value, there is a moving subject. Therefore, the amount of movement is simply calculated from the peak-to-peak absolute value of the difference. From this amount of movement, the relative speed between the subject and the imaging device is calculated. For example, when it is recognized that the subject is moving 100 pixels or more continuously while moving one frame on the screen, α is set to 58, The mode is driven at the drive timing at which β is set to 0, and when the subject does not satisfy the above moving speed, the mode is driven at the drive timing at which α is set to 25 and β is set to 37. Alternatively, for example, when the exposure time is 1/2000 sec or less, the mode is driven at a driving timing in which α is set to 58 and β is set to 0, and when the exposure time is 1/2000 sec or more, α is set to 25 and β is set to The mode is driven at the drive timing set to 37. Alternatively, the mode is driven at a driving timing in which α is set to 58 and β is set to 0 for a mode that does not perform thinning in the horizontal direction, and α is set to 25 and β for a mode in which thinning is performed in the horizontal direction. The mode is driven at the drive timing set to 37.

  As described above, when the relative speed between the subject and the imaging device is larger than a predetermined value, or when the exposure time is shorter than the predetermined value, the time required for reading and transferring with the imaging device using a high-pixel imaging device. When subject distortion is conspicuous, such as when the subject is long, β is set to 0, that is, by adjusting the frame rate only with α, the drive timing is set so that the exposure time shift for each row on the image is reduced, and the subject distortion is noticeable. Can be eliminated.

  Further, an increase in the number of reference pulses in the horizontal scanning period causes problems such as an increase in the release time and an increase in the continuous shooting speed in addition to the subject distortion. For this reason, setting the number of reference pulses in the horizontal scanning period to be smaller as described above leads to shortening of the release time and the continuous shooting speed.

  Further, when the image pickup apparatus shown in the first embodiment is driven in the driving mode using the mechanical shutter, the frame rate is set by a method that is not restricted by the formulas 1 to 3, and the driving mode not using the mechanical shutter is shown in the first embodiment. When the imaging apparatus is driven, the frame rate is set in accordance with the conditions of the above expressions 1 to 3, and when the mechanical shutter is used, an increase in the release time and the continuous shooting speed can be suppressed.

The figure which showed the concept of exposure time control in the solid-state imaging device of this invention. The figure which showed the outline | summary of the solid-state image sensor in the solid-state imaging device of this invention. The figure which showed the color filter used for the solid-state image sensor in the solid-state imaging device of this invention. The figure which showed the outline | summary of the system in the solid-state imaging device of this invention. The figure which showed the drive pulse and operation | movement sequence at the time of the rolling electronic shutter operation | movement in the solid-state imaging device of this invention. The figure which shows an example of the pixel structure in a solid-state image sensor. The figure which showed an example of the drive signal of the solid-state image sensor in the conventional solid-state imaging device. The figure which showed the problem of the exposure time control in the solid-state image sensor using a rolling electronic shutter.

Explanation of symbols

201 unit pixel 202 photodiode 203 transfer switch 204 floating diffusion 205 amplification MOS amplifier 206 selection switch 207 reset switch 208 signal line 209 constant current source 210 selection switch 211 output amplifier 212 vertical scanning circuit 213 readout circuit 214 horizontal scanning circuit 401 lens unit 402 Lens Driving Unit 403 Mechanical Shutter 404 Mechanical Shutter Driving Unit 405 Imaging Element 406 Imaging Signal Processing Circuit 407 Timing Generation Unit 408 Memory Unit 409 Overall Control Operation Unit 410 Recording Medium Control Interface Unit 411 Recording Medium 412 External Interface Unit 413 Photometric Unit 414 Measuring Distance portion 601 Effective pixel area 602 Optical black area

Claims (7)

  In an XY address type solid-state image sensor, a drive signal is given to the solid-state image sensor so that a predetermined unit of video signal obtained from the solid-state image sensor includes a scanning period and a blanking period from the start of output to the end of output, and exposure starts. In a solid-state imaging device that controls exposure time so that the time and the readout start time are different in the row direction or the column direction of the video signal, the video signal period and the empty video signal period in which the video signal from the solid-state imaging device is not output are horizontally A solid-state imaging device characterized in that a desired frame rate is realized by setting an integral multiple of a scanning period or adjusting the length of all horizontal scanning periods.   2. The solid-state imaging device according to claim 1, wherein after setting a video signal period and an empty video signal period in which no video signal is output from the solid-state imaging device to be an integral multiple of a horizontal scanning period, the length of all horizontal scanning periods is set. A solid-state imaging device that achieves a desired frame rate by adjusting the height.   3. The solid-state imaging device according to claim 2, wherein when adjusting the frame rate, an extended period by adding a video signal period and an empty video signal period that does not output a video signal from the solid-state imaging element is included in all horizontal scanning periods. A solid-state imaging device characterized in that it is longer than the sum of extension periods.   The solid-state imaging device according to claim 1, wherein the relative velocity calculated by the relative-speed velocity measuring device is a predetermined value in the solid-state imaging device including a relative velocity measuring device that measures the relative velocity between the subject and the solid-state imaging device. If it exceeds the value, the video signal period and the empty video signal period in which no video signal is output from the solid-state imaging device are set to be an integral multiple of the horizontal scanning period, and the length is set for all horizontal scanning periods. A solid-state imaging device that realizes a desired frame rate by not extending the length.   2. The solid-state imaging device according to claim 1, wherein when the exposure time is shorter than a predetermined value, the video signal period and the empty video signal period in which the video signal from the solid-state imaging element is not output are an integral multiple of the horizontal scanning period. A solid-state imaging device that realizes a desired frame rate by setting so that the length is not extended for all horizontal scanning periods.   2. The solid-state imaging device according to claim 1, wherein when a time required for reading and transfer is longer than a predetermined value, a video signal period and an empty video signal period in which no video signal is output from the solid-state imaging element are set as a horizontal scanning period. A solid-state imaging device characterized in that a desired frame rate is realized by setting an integral multiple of the horizontal scanning period and not extending the length for all horizontal scanning periods.   A drive signal is given to the solid-state image sensor so that a predetermined unit of the video signal obtained from the solid-state image sensor includes a scanning period and a blanking period from the output start to the output end, and the exposure start time and readout start time are the video signal. In the solid-state imaging device that performs exposure time control differently in the row direction or the column direction, when the mechanical shutter is used for the exposure time control, the frame rate adjustment method according to claim 1 is not used. apparatus.

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