JP2009027253A - Image pickup device and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image pickup device capable of reducing the number of defective pixels for improving image quality in thin-out processing so that a defect correction mark does not become conspicuous, and to provide an imaging apparatus. <P>SOLUTION: In the image pickup device, pixels, which have a PD 202 for converting a signal corresponding to the quantity of incident light to charge, are arranged in a matrix. The image pickup device has a thin-out mode for selecting and thinning out pixel signals from a specified group for output. In the thin-out mode, there is a selection switch 206 used as a selection means for selecting a signal, where the signal of the PD 202 is minimized in the group. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging device and an imaging device equipped with the imaging device.

  2. Description of the Related Art Conventionally, imaging apparatuses such as digital cameras and digital video cameras that use a CCD or CMOSAPS as an imaging element and record a captured image have become widespread. In order to increase the resolution of a still image, there are many image sensors used in these applications that have a number of pixels of several million pixels or more. Recently, there are an increasing number of image sensors with more than 10 million pixels.

  However, in recent years, not only digital video cameras but also digital cameras have been used for moving images. In an image pickup apparatus having such a moving image shooting function, the number of necessary pixels differs between moving image shooting and still image shooting, and therefore, resolution conversion is necessary.

  Usually, since the moving image resolution is lower than the still image resolution, an image sensor having a large number of pixels equal to or higher than the moving image resolution needs to have a low pixel count for moving image use.

  For example, since the moving image resolution in the HD format generally called FullHD is 1920 × 1080 and about 2 million pixels, it is necessary to reduce the number of pixels in the case of an image sensor having a resolution higher than that.

  As a method for reducing the number of pixels, there are a thinning process in which pixels are skipped in a specific period, an addition process in which pixel signals are added in a specific period, and a crop in which only a specific pixel area is read out. As these processing methods, various methods such as a method of reading all pixels from the image sensor and performing the image processing unit (image signal processing circuit), a method of performing the image sensor, and the like have been proposed.

  When reading with a reduced number of pixels in the image sensor, the amount of data transferred from the image sensor to the image processing unit is reduced compared to the method of reducing the number of pixels read by the image processing unit. From the viewpoint of

  By the way, since there exists a pixel defect in an image pick-up element and there exists a problem which image quality deteriorates by a pixel defect, the method of improving an image quality by correcting a pixel defect is used.

  However, when pixel defect correction is performed, a signal different from the conventional pixel signal is generated. Therefore, there is a scene in which a trace of pixel defect correction is conspicuous in a specific scene. Therefore, although pixel defects always exist, an image with high image quality can be obtained with as few as possible.

Therefore, it is desirable from the viewpoint of image quality to select a pixel with as few defects as possible for a pixel that outputs a signal in an image sensor that reads out by thinning-out processing. There is a technique disclosed in Patent Document 1 for reading an image with few pixel defects at the time of thinning. This technique reads out a field with few defective pixels when thinning out.
JP 2006-245999 A

  However, the number of defective pixels is relatively small in the image sensor, and whether or not the number of defective pixels is small enough not to affect the image quality is due to chance. That is, it cannot necessarily be said that there are few pixel defects. Further, since correction is performed by a signal processing circuit outside the image sensor, a memory for storing address information of defective pixels is also required.

  An object of the present invention is to provide an imaging device and an imaging apparatus capable of reducing defective pixels and improving image quality when thinning processing is performed so that traces of defect correction are not conspicuous.

  In order to achieve the above-described object, the image sensor according to claim 1 is an image sensor in which pixels having photoelectric conversion elements that convert a signal corresponding to an incident light amount into charges are arranged in a matrix, and the signal of the pixel. A thinning mode for selecting and thinning out a specific group for output, and in the thinning mode, a selection means for selecting a signal that minimizes the signal of the photoelectric conversion element in the group. To do.

  An image pickup apparatus according to a fifth aspect includes the image pickup element according to the first aspect.

  According to the present invention, when thinning processing is performed so that the trace of defect correction is not conspicuous, it is possible to reduce defective pixels and improve image quality.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram schematically showing a configuration of an image sensor according to an embodiment of the present invention.

  In FIG. 1, the imaging device includes a pixel portion 101, a column readout circuit 102, a row driver 103, and a column driver 104.

  The pixel unit 101 has pixels arranged in the vertical direction and the horizontal direction. Specifically, pixels having photoelectric conversion elements that convert a signal corresponding to the amount of incident light into electric charges are arranged in a matrix. The column readout circuit 102 that reads out the signal of the pixel unit 101 reads out the output of the pixel in the row selected by the row driver 103. The signal recorded in the column readout circuit 102 is selected and output by the column driver 104.

  FIG. 2 is a diagram illustrating a first configuration example of one pixel in the image sensor of FIG.

  In the imaging device, a pixel array that provides a two-dimensional image is configured by arranging a plurality of pixels in a two-dimensional array (matrix).

  The image pickup device of the present invention has a thinning mode in which pixel signals are selected from a specific group and thinned and output. In the thinning mode, a signal that minimizes the signal of a photodiode as a photoelectric conversion element in the group is obtained. select.

  Each pixel 201 includes a photodiode (hereinafter also referred to as PD) 202, a transfer switch 203, a floating diffusion portion (hereinafter also referred to as FD) 204, an amplification MOS amplifier (amplifier) 205, a selection switch (selection means) 206, and a reset switch. 207.

  The PD 202 functions as a photoelectric conversion element that photoelectrically converts light incident through the optical system. The anode of the PD 202 is connected to the ground line (ground side), and the cathode is connected to the source (source follower side) of the transfer switch 203.

  The transfer switch 203 is driven by a transfer pulse φTX input to its gate terminal, and transfers charges generated in the PD 202 to the FD 204. The FD 204 functions as a charge-voltage conversion unit that temporarily accumulates charges and converts the accumulated charges into a voltage signal.

  An amplification MOS amplifier 205 as an amplifier is provided for each pixel, operates with the signal of the PD 202 as an input, and outputs are connected to the same wiring. The amplification MOS amplifier 205 functions as a source follower, and a signal that has been subjected to charge-voltage conversion by the FD 204 is input to its gate. The amplification MOS amplifier 205 has its drain connected to the first power supply line VDD1 that provides the first potential, and its source connected to the selection switch 206.

  The selection switch 206 is driven by a vertical selection pulse φSEL input to its gate, its drain is connected to the amplification MOS amplifier 205, and its source is connected to the vertical signal line 208. When the vertical selection pulse φSEL becomes an active level (high level), the selection switches 206 of the pixels belonging to the corresponding row of the pixel array are turned on, and the source of the amplification MOS amplifier 205 is connected to the vertical signal line 208.

  The reset switch 207 has a drain connected to a second power supply line VDD2 that provides a second potential (reset potential), a source connected to the FD 204, and is driven by a reset pulse φRES input to the gate. . Then, charges accumulated in the FD 204 are removed.

  In addition to the FD 204 and the amplification MOS amplifier 205, a floating diffusion amplifier is configured by a constant current source (not shown) that supplies a constant current to the vertical signal line 208. In each pixel constituting the row selected by the selection switch 206, the charge transferred to the FD 204 is converted into a voltage signal by the FD 204 and output to the corresponding column readout circuit 102 through the floating diffusion amplifier.

  FIG. 3A shows a 9 × 9 pixel arrangement and a readout circuit, and FIG. 3B shows a relationship between the readout row and time. Alphabets a to i indicate row numbers, and numerals 1 to 9 indicate column numbers. A method of grouping by 3 rows or 3 rows by 3 columns and selecting the minimum value among them will be described with reference to FIG.

  T1, t3, and t5 shown in FIG. 3B are row selection periods. In the row selection period, first, the reset of the reset switch 207 is released, and then the charge of the PD 202 is transferred to the FD 204. When the selection switch 206 is turned on, an output corresponding to the potential of the FD 204 is transmitted to the vertical signal line 208.

  In the row selection period t1, since the selection switches 206 for the pixels in the a row, the b row, and the c row are simultaneously turned on, the output of the amplification MOS amplifier 205 competes on the signal output line.

  Here, a case where the outputs of the amplification MOS amplifier 205 compete is considered. First, considering the potential of the FD 204, the FD 204 is at the potential VDD2 reset via the reset switch 207 at the start of row selection.

  When the charge of the PD 202 is transferred to the FD 204, the potential decreases from the potential VDD2 by the amount of charge generated in the PD 202. For example, when the charges generated in the PD 202 are 10 and 1000, the potential is higher for 10 and the potential is lower for 1000.

  Next, considering the output of the amplification MOS amplifier 205, since the amplification MOS amplifier 205 has the FD 204 connected to the gate, the output of the amplification MOS amplifier 205 is higher when the gate potential is higher.

  That is, the output of the corresponding amplification MOS amplifier 205 is higher when the charge generated in the PD 202 is smaller. When amplification MOS amplifiers 205 having different outputs are simultaneously connected to the signal output line, the potential of the signal output line becomes a signal of the amplification MOS amplifier 205 having a high output.

  Therefore, when the amplification MOS amplifier 205 that reads the PDs 202 having different generated charges is connected to the signal output line, the value of the amplification MOS amplifier 205 that transmits the signal of the PD 202 with a small amount of generated charges to the signal output line becomes the signal value.

  That is, in the row selection period t1, the value of the pixel with the least amount of generated charge among the a row, b row, and c row is output to the signal output line. A defective pixel generally has a large amount of generated charges because of excessive charges.

  Therefore, for example, when the generated charge amount is a row> b row> c row and the a row is a defective pixel, a signal of the pixel in the c row is output. Similarly, pixels with few outputs are selected in the d row, e row, and f row in the row selection period t3, and in the g row, h row, and i row in the row selection period t5.

  t2, t4, and t6 are horizontal transfer periods, and a signal recorded in the column readout circuit 102 is output by the column driver 104.

  The selection of the minimum value in the column direction can be achieved by having a similar amplification MOS amplifier in the column readout circuit 102. In addition, by having a switch that is short-circuited in the horizontal direction between the pixel unit 101 and the column readout circuit 102, it is possible to select the minimum value in units of blocks selected in the horizontal direction and the vertical direction.

  For example, when a row, b row, and c row are selected and the signal output lines of the first, second, and third columns are short-circuited, the minimum value is selected from 3 rows × 3 columns.

  In FIG. 3, the pixel arrangement of 9 rows and 9 columns is shown, but the description is simplified and not limited to 9 rows and 9 columns. Although the case of thinning out to 1/3 in each column direction is described, it is not particularly limited to 1/3, and the number of pixels to be read simultaneously may be determined in accordance with the thinning rate intended by the photographer.

  In FIG. 3, the selection of the minimum value between consecutive pixels has been described. However, this is not limited to the case where a color filter is arranged, and the correspondence can be achieved by simultaneously selecting the signals of pixels of the same color.

  FIG. 4 is a diagram illustrating a second configuration example of one pixel in the image sensor of FIG.

  4 does not have the selection switch 206 of FIG. 2, and the potential of the floating diffusion is lowered to near GND by changing the potential of VDD2, thereby turning off the source follower driver MOS 205 and turning off the pixel selection. Are shown.

  In this pixel, since the pixel is selected by using the reset switch 207, essentially the same operation as that in which the pixel amplifier is connected to the output line by the selection switch 206 in FIG. 2 is possible.

  In the normal reading mode other than the thinning mode in which thinning is performed, the normal reading mode can be executed by not selecting the respective rows in FIG. 3 at the same time. In this case, defective pixels are not reduced. However, if there is a memory for storing address information of defective pixels and correction is performed by a signal processing circuit outside the image sensor, defective pixels can be reduced by correcting defective pixels. Is possible.

  That is, defect correction in the signal processing circuit is not necessary in the thinning mode. The presence or absence of defect correction of the signal processing circuit can be changed according to the thinning mode and the normal reading mode. In the thinning mode, the operation of the signal processing circuit that performs defect correction is not performed, so that a merit such as reduction in power consumption can be obtained.

  FIG. 5 is a diagram schematically showing the configuration of the imaging apparatus according to the embodiment of the present invention.

  In FIG. 5, a lens unit 501 forms an optical image of a subject on an image sensor 505, and zoom control, focus control, aperture control, and the like are performed by a lens driving device 502. The mechanical shutter 503 is controlled by a shutter driving device 504. The image sensor 505 captures the subject imaged by the lens unit 501 as an image signal.

  The imaging signal processing circuit 506 performs amplification of the image signal output from the imaging element 505, A / D conversion (analog / digital conversion), various corrections to the image data after A / D conversion, data compression, and the like. .

  The timing generator 507 outputs various timing signals to the image sensor 505 and the image signal processing circuit 506. The memory unit 508 temporarily stores image data. The overall control / calculation unit 509 performs various calculations and controls the entire imaging apparatus.

  The recording medium control I / F unit 510 is an interface for performing recording or reading on the recording medium 511. A removable recording medium 511 such as a semiconductor memory records or reads image data. The external I / F unit 512 is an interface for communicating with an external computer or the like.

  A photometric device 513 and a distance measuring device 514 are also connected to the overall control / calculation unit 509.

  Next, the operation of the image pickup apparatus at the time of shooting will be described.

  When the main power supply is turned on, the power supply for the control system is turned on, and the power supply for the image pickup system circuit such as the image pickup signal processing circuit 506 is turned on.

  Then, when a release button (not shown) is pressed, a high frequency component is extracted based on the signal output from the distance measuring device 514, and the distance to the subject is calculated by the overall control / calculation unit 509.

  After that, the lens unit 501 is driven by the lens driving device 502 to determine whether or not it is in focus. When it is determined that the lens unit 501 is not in focus, the lens unit 501 is driven again to perform distance measurement. Then, after the in-focus state is confirmed, the photographing operation starts.

  When the photographing operation is completed, the image signal output from the image sensor 505 is subjected to processing such as amplification and A / D conversion by the image signal processing circuit 506, and is written to the memory unit 508 by the overall control / calculation unit 509.

  Thereafter, the data stored in the memory unit 508 is recorded on the recording medium 511 through the recording medium control I / F unit 510 under the control of the overall control / calculation unit 509. Further, the data stored in the memory unit 508 may be directly input to a computer or the like via the external I / F unit 512 to process the image.

1 is a diagram schematically showing a configuration of an image sensor according to an embodiment of the present invention. It is a figure which shows the 1st structural example of 1 pixel in the image pick-up element of FIG. FIG. 2 is a diagram illustrating a time relationship between pixel arrangement and readout in the image sensor of FIG. 1. It is a figure which shows the 2nd structural example of 1 pixel in the image pick-up element of FIG. 1 is a diagram schematically illustrating a configuration of an imaging apparatus according to an embodiment of the present invention.

Explanation of symbols

101 Pixel unit 102 Column readout circuit 103 Row driver 104 Column driver 201 Pixel 202 PD
203 Transfer switch 204 FD
205 Amplification MOS amplifier 206 Selection switch 207 Reset switch 208 Vertical signal line

Claims (5)

In an image sensor in which pixels having photoelectric conversion elements that convert a signal corresponding to the amount of incident light into charges are arranged in a matrix,
A thinning mode in which the pixel signal is selected from a specific group and thinned and output; and in the thinning mode, selection means for selecting a signal that minimizes the signal of the photoelectric conversion element in the group An image sensor characterized by the above.   Each pixel has an amplifier that operates using the signal of the photoelectric conversion element as an input and the output is connected to the same wiring, and outputs the output of the amplifier of the pixels belonging to the group to the wiring at the same time in the thinning mode The imaging device according to claim 1, wherein:   The imaging device according to claim 2, wherein the amplifier functions as a source follower.   4. The image pickup device according to claim 3, wherein the photoelectric conversion element includes a photodiode, and the photodiode has a cathode connected to the source follower side and an anode connected to the ground side.   An imaging device comprising the imaging device according to claim 1.

Images