JP2016029759A - Defective pixel detection method for imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-precision defective pixel detection system in which temperature unevenness occurring within a sensor plane when the temperature of a sensor increases is set to a one-dimensional temperature distribution by driving means of the sensor, whereby a detection error caused by the temperature unevenness can be reduced without requiring any temperature adjusting facilities such as a constant temperature bath or the like and any temperature distribution measuring unit such as a thermography or the like.SOLUTION: A defective pixel detection system for an imaging element that is capable of detecting defective pixel information of a solid-state image pickup device has: a solid-state image pickup device including a plurality of pixels; an image pickup device driving unit comprising first driving means, and second driving means capable of intercepting power supply of a part of a driving circuit operating during a normal imaging operation of the solid-state image pickup device and operating under this state in the driving circuit; temperature detecting means for detecting the temperature of the solid-state image pickup device; and correction means for correcting a defective pixel detection threshold value according to the temperature detected by the temperature detecting means.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an improvement of a defective pixel detection method in an imaging apparatus capable of detecting defective pixel information of a solid-state imaging device having a plurality of pixels.

  In an imaging apparatus such as a digital camera or a video camera, a CCD or a CMOS image sensor is generally used as an imaging element.

  It is well known that the characteristics of the image sensor include defective pixels due to the dark current of the photodiode for each pixel, and these deteriorate the image quality of the captured image.

  The dark current is generally said to increase by a factor of 2 with a temperature increase of 8 ° C. The defective pixel due to the dark current of the photodiode has temperature characteristics. It is also well known that the number of defective pixels that require the increase.

  That is, in detecting defective pixels, by increasing the temperature of the image sensor, it is possible to accurately detect defective pixels without leaking even minute defective pixels.

  By the way, detection of defective pixels is generally performed in an environment at room temperature. However, in consideration of the increase in the number of defective pixels at high temperatures as described above, detect defective pixels at a temperature higher than normal temperature. In this case, in order to place the imaging device in a higher temperature environment, for example, equipment such as a thermostatic bath is required. In this case, not only the equipment necessary for detecting defective pixels increases, but also the temperature of the image sensor inside the camera body rises because the imaging device is heated from the outside of the camera body. Takes time, that is, it takes a long time to complete the defective pixel detection. For these reasons, there is a demand for a technique that realizes a high-temperature state in a camera and enables detection of defective pixels.

  As described above, as a method for detecting defective pixels caused by dark current of a photodiode having temperature characteristics, a defective pixel detection method corresponding to the number of defective pixels due to a temperature change without requiring a thermostat is disclosed. ing. In Patent Document 1, the temperature control is performed inside the imaging apparatus by, for example, driving to increase power consumption such as live view driving without requiring a constant temperature bath or the like, and the number of defective pixels due to temperature change of the sensor surface. A defective pixel detection technique corresponding to a change is disclosed.

  Further, in Patent Document 2, a defective pixel detection threshold value or a defective pixel signal value is corrected for each block in accordance with temperature unevenness in the sensor surface due to each temperature at a certain location, which has been measured in advance, to thereby detect defective pixels. A technique for detecting the above is disclosed.

JP 2010-118780 A Japanese Unexamined Patent Publication No. 2007-12948

  FIG. 15 is a simplified diagram of an image sensor. Reference numeral 1501 denotes an image sensor. An output amplifier 1502 outputs a signal from the pixel unit to the subsequent stage. Reference numeral 1503 denotes a pixel portion including a photodiode or the like. The temperature distribution of the pixel portion 1503 is represented by light colors of high temperature and dark colors of low temperature. In the figure, column circuit blocks and horizontal scanning circuits are arranged above and below the pixel portion 1503, and a vertical scanning circuit is arranged on the left side. FIG. 16 is a graph of the temperature in the sensor surface and the signal level of the defective pixel.

  Patent Document 1 is very effective when the image sensor 1501 undergoes a uniform temperature change, but actually generates heat by the output amplifier 1502 and the column circuit of the image sensor internal circuit, and as shown in FIG. In addition, a part of the image sensor close to the heat source partially rises in temperature, and the defective pixel level is different between the high temperature part and the low temperature part in the image sensor. Similarly, if the threshold is fixed, a defective pixel cannot be detected properly.

  In Patent Document 2, in view of the above-described problems, correction is performed in consideration of temperature unevenness. However, in order to measure complicated two-dimensional temperature unevenness in the inspection process, temperature distribution such as thermography is used. There is a disadvantage that a measuring instrument has to be used, and the labor of adding a process of temperature distribution measurement is increased.

  In order to detect defective pixels with high accuracy, it is desirable that the defective pixels have a temperature characteristic derived from dark current, so that the imaging element is at a high temperature. However, if the temperature distribution in the surface of the image sensor becomes a two-dimensional complicated distribution even when the image sensor is in a high temperature state, a means for measuring the two-dimensional temperature distribution becomes necessary.

  Therefore, the present invention drives the sensor so that the temperature unevenness that occurs in the sensor surface when the temperature of the sensor rises has a one-dimensional distribution, so that a temperature distribution measuring instrument such as a temperature control facility such as a thermostatic bath or a thermography. Therefore, it is an object of the present invention to realize an accurate defective pixel detection system in which detection errors due to temperature unevenness are reduced.

  The present invention provides a defective pixel detection system for an image sensor capable of detecting defective pixel information of a solid-state image sensor, and a solid-state image sensor having a plurality of pixels and a drive circuit for driving the solid-state image sensor during normal imaging. An image sensor driving unit including one driving unit and a second driving unit capable of driving in a state where power supply to some of the driving circuits can be cut off; and a temperature of the solid-state imaging device A solid-state imaging device defective pixel detection system comprising: a temperature detection unit that detects the temperature difference; and a correction unit that corrects a defective pixel detection threshold according to the temperature detected by the temperature detection unit.

  In the defective pixel detection mode, the temperature distribution in the sensor surface is driven by a driving means that becomes a one-dimensional monotonous distribution when the temperature rises. It is possible to provide an accurate defective pixel detection system in which detection error due to temperature unevenness is reduced, which is not necessary.

It is a block diagram of the imaging device in Example 1 of the present invention. It is a defective pixel detection threshold value correction coefficient table in the defective pixel detection mode in Embodiment 1 of the present invention. It is a circuit diagram of the CMOS type area sensor in Example 1 of this invention. It is a figure showing the temperature distribution of the CMOS type area sensor pixel part at the time of the defective pixel detection mode in Example 1 of this invention. It is a timing chart at the time of the temperature rise mode in Example 1 of this invention. It is a timing chart at the time of the defective pixel imaging | photography mode in Example 1 of this invention. It is an arrangement plan of a temperature detector used for temperature measurement of a CMOS type area sensor in Example 1 of the present invention. It is a table | surface showing the temperature and defective pixel detection correction coefficient of each block of the CMOS type area sensor pixel part at the time of the defective pixel detection mode in Example 1 of this invention. It is a timing chart of the CMOS type area sensor at the time of the defective pixel detection mode in Example 1 of this invention. It is a flowchart at the time of the defective pixel detection mode in Example 1 of this invention. It is a circuit diagram of the CMOS type area sensor in Example 2 of this invention. It is a timing chart at the time of the temperature rise mode in Example 2 of the present invention. It is a timing chart at the time of the defective pixel imaging | photography mode in Example 2 of this invention. It is a figure showing the temperature distribution of the CMOS type area sensor pixel part at the time of the defective pixel detection mode in Example 2 of this invention. It is a figure showing the temperature distribution of the sensor at the time of the defective pixel detection mode in a prior art. It is a figure which shows the relationship between the signal level and temperature of a defective pixel in a prior art.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

[Example 1]
An example of an imaging apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram illustrating a configuration example of an imaging apparatus according to Embodiment 1 of the present invention. Reference numeral 1 denotes an optical system including a lens and a diaphragm. Reference numeral 2 denotes a mechanical shutter (shown as a mechanical shutter). Reference numeral 3 denotes an image sensor. Reference numeral 4 denotes a CDS circuit that performs analog signal processing. Reference numeral 5 denotes an A / D converter that converts an analog signal into a digital signal. Reference numeral 6 denotes a timing signal generation circuit that generates signals for operating the image pickup device 3, the CDS circuit 4, and the A / D converter 5. Reference numeral 7 denotes a drive circuit for the optical system 1, the mechanical shutter 2, and the image sensor 3.

  A signal processing circuit 8 performs necessary signal processing on the captured image data. Reference numeral 9 denotes an image memory for storing image-processed image data. Reference numeral 10 denotes an image recording medium that can be detached from the imaging apparatus. Reference numeral 11 denotes a recording circuit that records image-processed image data on the image recording medium 10. Reference numeral 12 denotes an image display device that displays image data subjected to signal processing. A display circuit 13 displays an image on the image display device 12. A system control unit 14 controls the entire imaging apparatus.

  Reference numeral 15 denotes a nonvolatile memory (ROM) for storing a program describing a control method executed by the system control unit 14 and control data such as parameters used when the program is executed. Reference numeral 16 denotes a volatile memory (RAM) that transfers and stores the program, control data, and correction data stored in the nonvolatile memory 15 and is used when the system control unit 14 controls the imaging apparatus. Reference numeral 17 denotes a temperature detection unit. It is configured to include a temperature measuring element such as a thermistor, and measures the temperature of the image sensor 3 and outputs it to the drive circuit 7 via the system control unit 14.

  The storage device 18 is a non-volatile memory that stores a defective pixel detection threshold correction coefficient table, address information of defective pixels, and levels thereof. An experimentally obtained threshold correction coefficient table (FIG. 2) uniquely determined by the temperature so as to be an appropriate defective pixel detection threshold corresponding to each temperature is created in advance and stored in this storage unit 18. deep. In FIG. 2, h> i> j> k> l> m> n.

  Hereinafter, a photographing operation (imaging method) using the mechanical shutter 2 using the imaging apparatus configured as described above will be described. Prior to the photographing operation, the system control unit 14 such as when the image pickup apparatus is turned on transfers the necessary program, control data, and correction data from the nonvolatile memory 15 to the volatile memory 16 and stores them when the operation is started. Shall. These programs and data are used when the system control unit 14 controls the imaging apparatus. At the same time, the system control unit 14 transfers and uses additional programs and data from the nonvolatile memory 15 to the volatile memory 16 or directly reads the data in the nonvolatile memory 15 as necessary.

  First, the optical system 1 drives a diaphragm and a lens according to a control signal from the system control unit 14 to form an object image set to an appropriate brightness on the image sensor 3. Next, the mechanical shutter 2 is driven by the control signal from the system control unit 14 so as to shield the image sensor 3 in accordance with the operation of the image sensor 3 so as to have a necessary exposure time.

  At this time, when the image pickup device 3 has an electronic shutter function, it may be used together with the mechanical shutter 2 to ensure a necessary exposure time. The image pickup device 3 is driven by a drive pulse based on an operation pulse generated by the timing signal generation circuit 6 controlled by the system control unit 14, and converts the subject image into an electrical signal by photoelectric conversion as an analog image signal. Output. The analog image signal output from the image pickup device 3 is subjected to an operation pulse generated by the timing signal generation circuit 6 controlled by the system control unit 14, and the clock synchronization noise is removed by the CDS circuit 4, so that the A / D converter 5 is converted into a digital image signal.

  Next, the signal processing circuit 8 controlled by the system control unit 14 performs image processing such as color conversion, white balance, and gamma correction, resolution conversion processing, and image compression processing on the digital image signal. The image memory 9 is used for temporarily storing a digital image signal during signal processing or for storing image data which is a digital image signal subjected to signal processing. The image data signal-processed by the signal processing circuit 8 and the image data stored in the image memory 9 are converted into data suitable for the image recording medium 10 (for example, file system data having a hierarchical structure) in the recording circuit 11. It is recorded on the image recording medium 10.

  In addition, after the resolution conversion process is performed by the signal processing circuit 8, the display circuit 13 converts the signal into a signal suitable for the image display device 12 (for example, an NTSC analog signal) and displays it on the image display device 12.

  Here, the signal processing circuit 8 may output the digital image signal as it is to the image memory 9 or the recording circuit 11 without performing signal processing by the control signal from the system control unit 14 as it is. Further, when requested by the system control unit 14, the signal processing circuit 8 sends the digital image signal and image data information generated in the signal processing process or information extracted from them to the system control unit 14. Output. The above information is, for example, information such as the spatial frequency of the image, the average value of the designated area, and the data amount of the compressed image.

  Further, the recording circuit 11 outputs information such as the type and free capacity of the image recording medium 10 to the system control unit 14 when requested by the system control unit 14.

  Further, a reproduction operation when image data is recorded on the image recording medium 10 will be described. The recording circuit 11 reads the image data from the image recording medium 10 by the control signal from the system control unit 14, and the signal processing circuit 8 also by the control signal from the system control unit 14 determines that the image data is a compressed image. Performs image decompression processing and stores it in the image memory 9. The image data stored in the image memory 9 is subjected to resolution conversion processing in the signal processing circuit 8, then converted into a signal suitable for the image display device 12 in the display circuit 13 and displayed on the image display device 12. .

  FIG. 3 is a circuit diagram of the CMOS area sensor (imaging device 3) according to the first embodiment of the present invention. A photodiode D1, a transfer switch M1, a reset switch M2, a pixel amplifier M3, and a row selection switch M4 are provided for each pixel. The gate of the transfer switch M1 is connected to the signal PTX from the vertical scanning circuit 111, the gate of the pixel reset switch M2 is connected to the signal PRES from the vertical scanning circuit 111, and the gate of the row selection switch M4 is connected to the signal from the vertical scanning circuit 111. Connected to the signal PSEL, the source part is connected to the vertical output line V. Reference numeral 122 denotes a column circuit block.

  A portion surrounded by a broken line at the bottom of FIG. 3 is a diagram in which the column circuit block 122 is written in detail. In the column circuit 122, a column amplifier 101 and a horizontal transfer switch M5 arranged for each column are provided. The gate of the horizontal transfer switch M5 is connected to the horizontal scanning circuit block. The column circuit block 122 and the horizontal scanning block 121 are arranged above and below the pixel portion. The pixel signal arranged in the odd column is sent to the lower column circuit block, and the pixel signal arranged in the even column is the upper column circuit. Although a model of two channels transmitted to the block is used as a model, the present invention is not limited to this configuration.

  The output amplifier 130 sequentially outputs the signal of each pixel in the row unit in the column circuit block to the CDS block 4 by the signal of the horizontal scanning circuit block. The output amplifier control switch 131 is a switch that controls power supply to the output amplifier 130. The gate portion is connected to the signal PG from the drive circuit 7. The drain part is connected to an output amplifier power supply (not shown).

  Next, the principle of the present invention will be described. As described above in the problem to be solved by the invention, in order to detect defective pixels derived from dark current with high accuracy without requiring new equipment, the imaging element is brought into a high temperature state in the imaging apparatus, and imaging is performed. It is important to detect defective pixels with a one-dimensional monotonous temperature distribution in the element plane.

  Therefore, description will be made with reference to FIG. 4 which is a simplified diagram of the present embodiment.

  FIG. 4A is a simplified diagram of FIG. Reference numeral 401 denotes an image sensor, 402 denotes a pixel portion, 130 denotes an output amplifier, and 131 denotes an output amplifier control switch. In the defective pixel detection system of the present embodiment, the temperature distribution of the pixel unit 402 when driven in the temperature increase mode is expressed by light color for high temperature and dark color for low temperature. The temperature increase mode will be described later. The block is divided into seven blocks A to G. FIG. 4B shows a graph of the relationship between the horizontal position in the sensor surface and temperature, and FIG. 4C shows a graph of the relationship between the vertical position in the sensor surface and temperature. Here, column circuit blocks and output amplifiers can be cited as typical heat sources of the image sensor.

  In order to obtain a one-dimensional simple temperature distribution using this heat source, the output amplifier control switch 131 that is normally turned on and turned off is turned off, and the sensor is driven so that the main heat source is only a column circuit. Therefore, the two-dimensional temperature distribution is not a conventional one, but a one-dimensional monotonic temperature distribution in the vertical direction as shown in FIG. That is, since the temperature in the sensor surface is nearly constant in the horizontal direction, there is no need to divide the block in the horizontal direction. Therefore, the number of blocks can be greatly reduced, and the memory capacity required for detecting defective pixels can be greatly reduced.

  Next, driving of two sensors performed in the defective pixel detection mode will be described.

  The first drive is set to the temperature rise mode. The temperature increase mode is driving for increasing the temperature in the sensor surface, which is performed in the defective pixel detection mode. FIG. 5 is a timing chart of the Nth row in the temperature rise mode. The driving is performed in the temperature rising mode during the period from t0 to t7. During the period from time t1 to t6, the signal PSEL (N) becomes active, the row selection switch M4 is turned on, and the source follower circuit configured by the pixel amplifiers M3 of all the pixels connected to the Nth row operates. It becomes a state. Here, in the period from time t2 to t3, the signal PRES (N) becomes active, the reset switch M2 is turned on, and the gate of the source follower M3 is initialized.

  Next, during the period from t4 to t5, the transfer switch M1 is turned on by making PTX (N) active. Thereby, the signal charge accumulated in the photodiode D1 is transferred to the gate of the source follower M3 constituted by the pixel amplifier M3. At this time, the potential of the gate of the source follower M3 configured by the pixel amplifier M3 varies from the reset level by an amount corresponding to the transferred signal charge, and the signal level is determined.

  This signal level is amplified by the column amplifier 101, and then M5 is sequentially driven by pulses from the horizontal scanning circuit 121 to horizontally scan the signal. At t0 when the temperature rise mode starts, the output amplifier control signal PG Since the output amplifier control switch 131 is turned off and the output amplifier is not driven, the signal is not output to the CDS block 4 in FIG. This completes the output of N rows. The signals PSEL (N + 1), PTX (N + 1), and PRES (N + 1) are also driven in the same manner as the Nth row, so that the (N + 1) th row is driven in the same manner.

  This driving is continued until a predetermined time (1 minute in this embodiment) elapses. By driving in the temperature rise mode, only the column circuit block generates heat among the main heat generation sources of the sensor, and the temperature in the sensor surface becomes nearly constant in the horizontal direction.

  The second drive is a defective pixel photographing mode. The defective pixel photographing mode is a drive for acquiring a still image in the dark after raising the temperature of the sensor surface in the temperature rising mode. The defective pixel imaging mode is composed of batch reset for resetting all the electrons accumulated in the photodiode D1 in the temperature rise mode, accumulation for performing photoelectric conversion of the still image in the dark while maintaining the temperature, and reading for reading the accumulated charge. Is done.

  FIG. 6 is a timing chart in the defective pixel photographing mode. During the period from t0 to t17, the driving is performed in the defective pixel photographing mode.

  Batch reset is performed during the period from t1 to t4. During the period from t1 to t4, the vertical scanning signals PSEL of all the rows are activated, all the row selection switches M4 are turned on, and the source follower circuit configured by the pixel amplifiers M3 of all the pixels is activated. Here, the reset signal PRES and the row selection signal PTX are activated during the period from the time t2 to the time t3, the reset switch M2 and the transfer switch M1 are turned on, and accumulated in the gates of the source followers M3 and the photodiodes D1 of all the pixels. The charge is reset.

  During the period from t5 to t9, temperature is maintained and accumulated. During a period from t5 to t8, when the vertical control signal PSEL (N) of an Nth row becomes active, the row selection switch M4 of the Nth row is turned on, and the pixel amplifier M3 of all the pixels connected to the Nth row The configured source follower circuit is activated. During a period from t6 to t7, the pixel reset signal PRES (N) becomes active, so that the reset switch M2 is turned on and the gate of the source follower M3 is initialized. Further, during the period from t5 to t8, the row selection signal PTX and the output amplifier control signal PG are fixed to LOW, so that the transfer switch M1 and the output amplifier control switch 131 are turned off.

  This completes the driving of N rows. The signals PSEL (N + 1), PTX (N + 1), and PRES (N + 1) are also driven in the same manner as the Nth row, so that the (N + 1) th row is driven in the same manner. By driving the column circuit with the transfer switch M1 turned off and the output amplifier stopped, it is possible to hold the temperature raised in the temperature rise mode while accumulating still images with the photodiode D1. Become. Driving during the period from t5 to t8 is repeated for the period from t9.

  Reading is performed during the period from t9 to t17. By activating the output amplifier control signal at timing t9, the output amplifier control switch is turned on and the output amplifier is driven. Next, during a period from time t10 to t15, the signal PSEL (N) becomes active, the row selection switch M4 is turned on, and the source follower circuit configured by the pixel amplifiers M3 of all the pixels connected to the Nth row. Becomes operational. Here, in the period from time t11 to t12, the signal PRES (N) becomes active, the reset switch M2 is turned on, and the gate of the source follower M3 is initialized.

  Next, during the period from t13 to t14, the transfer switch M1 is turned on by making PTX (N) active. Thereby, the signal charge accumulated in the photodiode D1 is transferred to the gate of the source follower M3 constituted by the pixel amplifier M3. At this time, the potential of the gate of the source follower M3 configured by the pixel amplifier M3 varies from the reset level by an amount corresponding to the transferred signal charge, and the signal level is determined.

  After the signal level is amplified by the column amplifier 101, the horizontal transfer switch M5 is sequentially driven by the pulse from the horizontal scanning circuit 121, thereby horizontally scanning the signal, and the timing from time t16 to time t17 in time series. Is output. This completes the output of N rows. The signals PSEL (N + 1), PTX (N + 1), and PRES (N + 1) are also driven in the same manner as the Nth row, whereby the N + 1th row signal can be read.

  Next, a temperature detection method and a defective pixel detection threshold value correction method will be described.

  Assuming that there is no difference between the sensor surface temperature and the sensor back surface temperature, for example, the temperature detector is provided with a plurality of temperature detectors, one for each block as shown in FIG. In FIG. 7, reference numeral 701 denotes the back surface of the image sensor. Reference numerals 702 (a) to 702 (g) denote temperature detectors.

  Based on the temperature detected by the temperature detection unit, the signal processing circuit 8 converts the threshold correction coefficient table (FIG. 2) stored in the storage unit 18 into a defective pixel detection threshold correction coefficient corresponding to each temperature, A defective pixel detection threshold value for each block is determined. In this embodiment, as shown in FIG. 8, the region A is 50 ° C., the region B is 48 ° C., the region C is 44 ° C., the region D is 42 ° C., the region E is 44 ° C., the region F is 47 ° C., and the region G is 51 °. Suppose that it was ℃. When the threshold value at normal temperature is set as the reference threshold value α in comparison with the threshold correction coefficient table, the threshold values of the respective regions are hα, iα, jα, kα, jα, iα, hα in the order of A to G, and each region corresponds to the temperature. The defective pixel detection threshold is determined.

  Next, sensor driving in the defective pixel detection mode will be described with reference to a timing chart (FIG. 9). The alternate long and short dash line in the column circuit operation indicates the column circuit drive in the temperature rise mode, the alternate long and two short dashes line indicates the temperature holding drive in the defective pixel photographing mode, and the solid line indicates the still image reading drive in the defective pixel photographing mode.

  At time t0, the defective pixel detection mode starts, and the sensor drive is changed from the normal drive to the temperature increase mode. During the period from t0 to t1, the temperature rise mode is driven for 1 minute with the time for the temperature to become steady for 1 minute (1800 frames when the frame rate is 30 fps).

  At t1, the sensor drive is switched from the temperature increase mode to the defective pixel imaging mode. All pixels are reset during the period from t1 to t2. During the period from t2 to t3, the photodiode circuit accumulates while driving the column circuit in the defective pixel photographing mode and maintaining the sensor temperature. The temperature detection unit 702 detects the temperature of the sensor at time t3. Also, by making the output amplifier control signal PG active from LOW, the output amplifier control switch is turned on and the output amplifier is made operable.

  During the period from t3 to t4, readout driving is performed, and the sensor ends driving in the defective pixel detection mode.

  Finally, the flow of the present embodiment will be described with reference to the flowchart (FIG. 10) of the defective pixel detection system for the image sensor in the present embodiment.

  After setting the camera to the defective pixel detection mode, the temperature increase mode is started to increase the temperature of the sensor surface (step S1). Here, at the time when the defective pixel detection mode starts, the temperature of the image sensor 3 is assumed to be lower than the target temperature at which the defective pixel is to be detected.

  Next, it is determined whether or not the system control unit 14 has been driven for a predetermined time (step S2). After driving for 1 minute, the temperature increase mode ends (step S3), and the defective pixel imaging mode starts (step S4).

  Next, all the charges stored in the photodiode D1 are reset (step S5). Next, while maintaining the temperature of the sensor surface, the photodiode D1 accumulates a still image in the dark (step S6). After a predetermined accumulation time, the temperature detector 602 detects the temperature of each block of the sensor (step S7).

  Next, the charge of the photodiode D1 is read (step S8), and the defective pixel photographing mode is ended (step S9). Image data obtained by photographing is transferred to the image memory 9 via the signal processing circuit 8. Using the threshold correction coefficient table, the defective pixel detection threshold value of each block is calculated according to the temperature (step S10). The calculated defective pixel detection threshold is compared with the pixel signal of each block, and a pixel exceeding the threshold is detected as a defective pixel (step S11). The memory 18 stores the address information detected as a defective pixel and the scratch level determined by the pixel output (step S12). This completes the defective pixel detection mode.

  By performing the drive described above, the temperature can be increased so that the temperature unevenness that occurs in the sensor surface within the camera becomes a one-dimensional distribution, and temperature distribution measurement such as temperature control equipment such as a thermostatic chamber or thermography. Therefore, it is possible to realize accurate defective pixel detection with reduced detection errors due to temperature unevenness without requiring a detector. The defective pixel detection method in the first embodiment is described above.

[Example 2]
The second embodiment of the present invention will be described. FIG. 11 is a circuit diagram of a CMOS area sensor according to the second embodiment of the present invention. The column amplifier control switch 132 is a power supply switch to the column amplifier 101 in the column circuit below the sensor. The gate portion of the column amplifier control switch 132 is connected to the column amplifier control signal PP from the drive circuit 7. The drain part is connected to the column amplifier power supply. Vg is a column amplifier power supply line. Other configurations are the same as those of the first embodiment.

  FIG. 12 is a timing chart of the temperature rise mode in the second embodiment. Similar to the output amplifier control signal at the timing t0 when the temperature rise mode starts, the column amplifier control signal PP is always LOW, so that the power supply switch 132 to the column amplifier 101 in the column circuit below the sensor is always turned off. The column amplifier 101 below the sensor is not driven. As a result, the heating unit to be driven is only the column circuit above the sensor, and the temperature distribution on the sensor surface is a one-dimensional monotonic temperature distribution in the vertical direction. Other signal timings are the same as those in the first embodiment.

  FIG. 13 is a timing chart in the defective pixel photographing mode in the second embodiment. Similarly to the output amplifier control signal PG, at the timing of reading starting at t9, the column amplifier control signal PP becomes active from LOW, so that the power supply switch to the column amplifier 101 in the column circuit below the sensor is turned on. The lower column amplifier 101 is driven. As a result, the signals of the pixels arranged in the odd columns can be read out. Other signal timings are the same as those in the first embodiment.

  FIG. 14 is a diagram showing the temperature distribution of the sensor in the defective pixel detection mode according to the second embodiment of the present invention. Reference numeral 1401 denotes an image sensor, 1402 denotes a pixel portion, 1403 denotes an output amplifier, 1404 denotes a power supply switch to the output amplifier 1403, and 1405 denotes a power supply switch to the lower column circuit block. The temperature distribution of the pixel portion 1402 is represented by light colors for high temperatures and dark colors for low temperatures. The upper graph shows the relationship between the horizontal position in the sensor plane and the temperature, and the right graph shows the relationship between the vertical position in the sensor plane and the temperature.

  In the second embodiment, in addition to the output amplifier 1403, a power supply switch 1405 is provided for the column amplifier below the sensor, and only the upper column circuit is driven at step S1 in FIG. The temperature distribution in the sensor plane can be controlled to a one-dimensional monotonous temperature distribution in the vertical direction.

  Similarly, a power supply switch may be provided in the column amplifier of the upper column circuit to drive the lower column circuit.

[Example 3]
In the two embodiments described above, a method is used in which a threshold value is determined for each block by applying a correction coefficient to the reference threshold according to the temperature of each block. Accordingly, a method of applying a correction coefficient to the pixel signal level of each block may be used. As in the defective pixel detection threshold correction table of FIG. 2, a signal value correction coefficient table obtained by experiment is created. The correction coefficient is u>t>s>r>q>p> o in descending order of temperature. A signal value correction coefficient table is created in advance in the storage device 18 of FIG. 1 and stored in this storage device 18.

  In step S10 in FIG. 10, the pixel value correction coefficient of each block is calculated by referring to the signal value correction coefficient table for each block according to the temperature of each block. Similarly to Example 1, the region A is 50 ° C., the region B is 48 ° C., the region C is 44 ° C., the region D is 42 ° C., the region E is 44 ° C., the region F is 47 ° C., and the region G is 51 ° C. For example, if the signal value of a pixel at a place where an X block is located is β (x), the signal value of a pixel of each block after correction is Oβ (a), pβ (b), qβ (c) in order from A to G. , Rβ (d), qβ (e), pβ (f), oβ (g). These corrected signal values are compared with a fixed threshold value to detect defective pixels. Other configurations are the same as those of the first embodiment.

  In the three examples shown here, one temperature detector is used for each block. For example, two temperature detectors are arranged in the upper part and the central part, and are obtained experimentally from the two temperatures. You may obtain | require the temperature of each block by applying to the approximate function of temperature distribution. In addition, the temperature measurement element may be embedded in each block or each row of the pixel portion instead of the back surface. That is, any arrangement can be used as long as the temperature of each block can be obtained. In this embodiment, a temperature measuring device is used. However, a temperature distribution can be estimated by using a technique that obtains a dark current from a difference between a reference level and a pixel dark output, and obtains a temperature from the dark current. Good.

  According to the first, second, and third embodiments of the present invention, when the temperature of the sensor rises, one-dimensional monotonous temperature distribution is generated by generating heat by driving off a part of the power supply of the heat source. The circuit drive is controlled so that the defective pixel is detected. Thereby, since the temperature distribution of the sensor can be easily grasped, accurate defective pixel detection with reduced detection error due to temperature unevenness can be realized without requiring new equipment.

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

D1 photodiode (PD), M1 transfer switch, M2 reset switch,
M3 source follower (pixel amplifier), M4 row selection switch,
M5 horizontal transfer switch, I load current source, V vertical output line,
Vg column amplifier power supply line, PTX row selection signal, PRES pixel reset signal,
PSEL vertical operation signal, PG output amplifier control signal, PP column amplifier control signal

Claims (5)

In a defective pixel detection system of an image sensor capable of detecting a defective pixel of a solid-state image sensor,
A solid-state imaging device having a plurality of pixels;
In the drive circuit that drives the solid-state imaging device during normal photographing, the first drive means and the second drive means that can cut off the power supply to some of the drive circuits and can drive in that state An image sensor driving unit comprising:
Temperature detecting means for detecting the temperature of the solid-state imaging device;
A defective pixel detection system for a solid-state imaging device, comprising: correction means for correcting a defective pixel detection threshold according to the temperature detected by the temperature detection means. In a defective pixel detection system of an image sensor capable of detecting defective pixel information of a solid-state image sensor,
A solid-state imaging device having a plurality of pixels;
In the drive circuit that drives the solid-state imaging device during normal photographing, the first drive means and the second drive means that can cut off the power supply to some of the drive circuits and can drive in that state An image sensor driving unit comprising:
Temperature detecting means for detecting the temperature of the solid-state imaging device;
A defective pixel detection system for a solid-state imaging device, comprising: correction means for correcting a pixel signal value in accordance with the temperature detected by the temperature detection means. 3. The defective pixel detection system according to claim 1, wherein the second driving unit is driven by cutting off power supplied to an output amplifier of the solid-state imaging device. 2. The second driving unit is configured to drive by cutting off a power supply to an output amplifier of the solid-state imaging device and a column circuit adjacent to either one of the upper side or the lower side of the solid-state imaging device. Or the defective pixel detection system of Claim 2. 3. The defective pixel detection system according to claim 1, wherein the driving by the second driving unit is continued during the accumulation period at the time of acquiring the light-shielded image.