Dead pixel detection, shielding and recovery method of time delay integral SPAD array

Abstract

The invention discloses a dead pixel detection, shielding and recovery method for a time delay integral SPAD array. The method comprises the following steps: step 1, detecting a count value of each pixel in the time delay integral SPAD array working in a detection mode in an exposure period; 2, sequentially outputting count values of all photons, judging whether a current pixel is a defective pixel or not according to a count value detection result, recording the position of the defective pixel, obtaining a shielding matrix according to the position of the defective pixel, and shielding the defective pixel according to the shielding matrix; and 3, when the SPAD array works in a TDI mode, outputting a photon count value after the last-stage pixel is exposed, and completing count value recovery according to the number of shielding pixels in the shielding matrix row where the count value is located. The SPAD pixel dead pixel shielding technology and the time delay integral SPAD array are combined, the influence of a certain-level dead pixel pixel in the SPAD array on the whole-level photon counting value is effectively reduced through sharing of the shielding technology and the recovery technology, and the effectiveness and stability of the SPAD array are greatly improved.

Description

Technical Field

[0001] The invention belongs to the field of integrated circuits, and in particular to a method for detecting, shielding and restoring bad points of a time-delayed integration SPAD array. Background Art

[0002] In recent years, photoelectric detection sensors have been widely used. Based on the single-photon avalanche diode detector (SPAD), the related time delay integration (TDI) array has been developed. The TDI chip based on the SPAD array has the advantages of low power consumption and high definition when shooting fast-moving objects. Pixels with SPAD devices as photosensitive units have the advantages of being sensitive to light and responding quickly, but they may have problems such as too high dark counts or no response, which makes the count value of this level too high or too low, that is, bad pixels appear. When a bad pixel appears in a certain level of the SPAD array of multi-level TDI and an erroneous count value is obtained, the erroneous count value will be transferred in each subsequent level of the circuit along with the transfer counter, and finally the array outputs the erroneous count value. For time-delay integration SPAD arrays with a higher number of levels, the photon count value of each row has to go through more pixels, and it is easier to encounter bad pixels in the transfer of a row.

[0003] SPAD pixel shielding technology has long existed. By controlling the driving circuit of a SPAD pixel, the pixel will be turned off, thereby achieving a shielding effect. However, although pixel shielding technology can achieve shielding, it cannot reduce the impact of a certain level of bad pixels in the SPAD array on the photon count value of the entire level, thereby affecting the effectiveness and stability of the SPAD array.

[0004] The use of pixel shielding technology in a time-delayed integration SPAD array, supplemented by bad pixel recovery technology, can effectively reduce the impact of bad pixels on the counting value in a multi-level SPAD array. Summary of the invention

[0005] The invention provides a bad pixel detection, shielding and recovery method of a time-delayed integration SPAD array, which is used to solve the defects in the prior art.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for detecting, shielding and restoring bad pixels of a time-delayed integration SPAD array comprises the following steps:

[0008] Step 1: Detect the count value of each pixel in the time-delayed integration SPAD array working in the detection mode within an exposure period;

[0009] Step 2: Output the count values ​​of all photons in sequence and determine whether the current pixel is a bad pixel based on the count value detection result and record the bad pixel position, obtain the shielding matrix from the bad pixel position, and shield the bad pixel through the driving circuit based on the shielding matrix;

[0010] Step 3: When the SPAD array works in TDI mode, the last level of pixels outputs a photon count value after completing exposure, and the count value is restored based on the number of shielded pixels in the shielding matrix row where the count value is located.

[0011] As described above, a method for bad pixel detection, shielding and recovery of a time-delayed integration SPAD array is described, wherein the time-delayed integration SPAD array operates in a detection mode, at which time all pixels of the array are exposed and record the number of photons within one exposure cycle, and then all pixels are turned off and the count values ​​are passed backward one level at a time until all are transmitted, and all the transmitted count values ​​are sent to a detection computer for bad pixel judgment, and if it is judged to be a bad pixel, it is recorded to obtain a shielding matrix.

[0012] As described above, a method for bad pixel detection, shielding and recovery of a time-delayed integration SPAD array is described, in which each pixel in the time-delayed integration SPAD array has an independent switch control unit, which is selected by a row and column bus according to a shielding matrix, and a configurable shutdown operation can be implemented at any position to complete the shielding. When the time-delayed integration SPAD array operates in TDI mode, the shielded pixel will transfer the count value of the previous level pixel to the next level pixel under the drive of the transfer signal.

[0013] The above-mentioned method for detecting, shielding and restoring bad pixels of a time-delayed integration SPAD array comprises a logic gate and a D flip-flop, and the input signal of the switch control unit is composed of a row-column bus of an open pixel, a row-column bus of a closed pixel, and an array switch; when the array switch is turned on, all pixels enter the working mode in sequence under the selection of the open row-column bus, and when the detection computer completes the judgment and obtains the shielding matrix, the shielded row-column bus is closed according to the selected pixel of the shielding matrix.

[0014] As described above, a bad pixel detection, shielding and recovery method of a time-delayed integration SPAD array, the time-delayed integration SPAD array belongs to a multi-level TDI array.

[0015] As described above, a method for detecting, shielding and restoring bad pixels of a time-delayed integration SPAD array determines whether the pixels at this level are damaged by detecting the count value of each pixel in each level of the TDI array, generates a shielding matrix based on the judgment result, and shuts down and shields the damaged pixels through a control circuit according to the shielding matrix. The transfer counter in the shut-off pixels directly transfers the photon count value of the previous level to the next level, and counts the number of shielded pixels in each row in the shielding matrix. Finally, the photon output value of the last level circuit of each row is compensated according to the number of shielded pixels in the shielding matrix to obtain a normal photon count value.

[0016] As described above, a method for bad pixel detection, shielding and recovery of a time-delayed integration SPAD array is described. The TDI array comprises M×L columns of pixels, including M×1 output column pixels and (L-1) M×1 front-stage column pixels. The M×L pixels in the TDI array are detected, and the detection can be achieved by a detection computer.

[0017] As described above, in a method for bad pixel detection, shielding and recovery of a time-delayed integration SPAD array, the detection computer reads out the photon count values ​​of all pixels in one exposure cycle, and then determines whether the count value of each pixel is too high or too low, and obtains a shielding matrix.

[0018] As described above, a method for detecting, shielding and restoring bad pixels of a time-delayed integration SPAD array is described, wherein the size of the shielding matrix is ​​M×L, and the elements are 1 or 0; if the count value is normal, the pixel is normal, and the mark position is 1; if the count value is too high or too low, it is judged that a bad pixel has appeared, and the mark position is 0; if a bad pixel appears in the xth row and yth column (x<=M, y<=L), the value of the (x, y) position in the shielding matrix is ​​changed to 0; the shielding matrix is ​​obtained after the detection computer completes all pixel judgments.

[0019] As described above, a method for detecting, shielding and recovering bad pixels of a time-delayed integration SPAD array is described. After completing the detection mode and shielding the pixels according to the shielding matrix, the time-delayed integration SPAD array can work normally in the TDI mode. At this time, it is assumed that the last level circuit of the x-th row outputs a photon count value Q after completing the exposure. The correct count value can be obtained by recovering Q, thereby reducing the influence of bad pixels on the result. The photon count value Q passes through M levels of pixels in total. It is assumed that N pixels are shielded for the count value. At this time, the x-th row in the shielding matrix corresponding to the SPAD array has N elements 0 and (MN) elements 1. The output photon count value Q is the photon count value result obtained within (MN) exposure cycles. The detection computer performs mathematical calculations based on the photon count value Q and the number N of element 0s in the row of the shielding matrix, Q r =Q / (MN)*M,Qr This is the photon count value obtained after the pixel array is shielded and repaired.

[0020] The advantages of the present invention are as follows: the present invention is based on the existing SPAD pixel bad pixel shielding technology, and combines the technology with the time-delayed integration SPAD array. By sharing the shielding technology and the recovery technology, the influence of a certain level of bad pixel in the SPAD array on the photon count value of the entire level is effectively reduced, thereby greatly improving the effectiveness and stability of the SPAD array, so that it can be applied to more complex environmental scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0022] Figure 1 It is a schematic diagram of the overall process of a bad pixel detection, shielding and recovery method applicable to a time-delayed integration SPAD array proposed by the present invention;

[0023] Figure 2 It is a structural diagram of a time-delayed integrated SPAD array of the present invention;

[0024] Figure 3 is a schematic diagram of a time-delayed integrated SPAD array of the present invention;

[0025] Figure 4 It is a schematic diagram of the bad pixel detection process of the present invention;

[0026] Figure 5 It is a process diagram of the detection computer of the present invention obtaining a shielding matrix according to the count value;

[0027] Figure 6 It is a schematic diagram of the detection computer of the present invention shielding bad pixel through the driving circuit according to the shielding matrix;

[0028] Figure 7 It is a schematic diagram of an array pixel control circuit of a bad pixel detection, shielding and recovery method of a time-delayed integration SPAD array of the present invention;

[0029] Figure 8 It is a schematic diagram of the bad point recovery method of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] like Figure 1 As shown, a method for detecting, shielding and restoring bad pixels of a time-delayed integration SPAD array comprises the following steps:

[0032] Step 1: The time-delayed integration SPAD array (its structure is as follows) working in the detection mode Figure 2 As shown, the time-delayed integration SPAD array usually adopts a 3D process and is divided into an upper and lower structure; the upper structure is mainly the pixel photosensitive part mainly composed of SPAD devices, and the lower structure is the pixel control circuit part; the upper SPAD devices are closely arranged to form a complete photosensitive layer, and its opening and closing are controlled by the lower control circuit; the lower control circuit layer contains the control circuits of all pixels, and each control circuit contains a driving circuit part. The driving circuit is affected by the bus and is turned on or off by the bus, thereby controlling the opening or closing of the pixel) to detect the count value of each pixel in an exposure cycle;

[0033] Step 2: Output the count values ​​of all photons in sequence and determine whether the current pixel is a bad pixel based on the count value detection result and record the bad pixel position, obtain the shielding matrix from the bad pixel position, and shield the bad pixel through the driving circuit based on the shielding matrix;

[0034] Step 3: When the SPAD array works in TDI mode, the last level of pixels outputs a photon count value after completing exposure, and the count value is restored based on the number of shielded pixels in the shielding matrix row where the count value is located.

[0035] Preferably, Figure 4 As shown, the time-delayed integration SPAD array described in this embodiment works in the detection mode. At this time, all pixels of the array are exposed to record the number of photons in one exposure cycle, and then all pixels are turned off and the count values ​​are passed backward one level at a time until all are transmitted. All the transmitted count values ​​are sent to the detection computer for bad pixel judgment. If it is judged to be a bad pixel, it is recorded to obtain a shielding matrix.

[0036] Preferably, Figure 3As shown, each pixel in the time-delayed integration SPAD array described in this embodiment has an independent switch control unit, which is selected by the row and column buses according to the shielding matrix, and can implement a configurable shutdown operation at any position to complete the shielding. When the time-delayed integration SPAD array operates in TDI mode, the shielded pixel will transfer the count value of the previous level pixel to the next level pixel under the drive of the transfer signal; the time-delayed integration SPAD array has M levels (M>1), with a size of M×L, and each level has SPAD pixels and control circuits. The control circuit contains a transfer counter and a driving circuit. Each control circuit can pass the count value to the next level control circuit and the detection computer, and receive the shielding instruction given by the detection computer. The last level control circuit can pass the count value to the latch and the address selection circuit for reading.

[0037] Preferably, the switch control unit described in this embodiment includes a logic gate and a D flip-flop, and the input signal of the switch control unit is composed of a row-column bus of an on pixel, a row-column bus of a turned-off pixel, and an array switch; when the array switch is turned on, all pixels enter the working mode in sequence under the selection of the on row-column bus, and when the detection computer completes the judgment and obtains the shielding matrix, the shielding row-column bus is selected according to the shielding matrix to close the pixel

[0038] Preferably, the time-delayed-integrated SPAD array described in this embodiment is a multi-level TDI array.

[0039] Preferably, Figure 6 As shown, this embodiment determines whether the pixels at this level are damaged by detecting the count value of each pixel in each level of the TDI array, generates a shielding matrix according to the judgment result, and shuts down and shields the damaged pixels through the control circuit according to the shielding matrix. The transfer counter in the shut-off pixels directly transfers the photon count value of the previous level to the next level, and counts the number of shielded pixels in each row in the shielding matrix. Finally, the photon output value of the last level circuit of each row is compensated according to the number of shielded pixels in the shielding matrix to obtain a normal photon count value.

[0040] Preferably, the TDI array described in this embodiment comprises M×L columns of pixels, including M×1 output column pixels and (L-1) M×1 front-stage column pixels. The M×L pixels in the TDI array are detected, and the detection can be achieved by a detection computer.

[0041] Preferably, after the detection computer described in this embodiment reads out the photon count values ​​of all pixels in one exposure cycle, the detection computer determines whether the count value of each pixel is too high or too low, and obtains a shielding matrix.

[0042] Preferably, Figure 5As shown, the size of the shielding matrix described in this embodiment is M×L, and the elements are 1 or 0; if the count value is normal, the pixel is normal, and the mark position is 1; if the count value is too high or too low, it is judged as a bad pixel, and the mark position is 0; if a bad pixel appears in the xth row and yth column (x<=M, y<=L), the value of the (x, y) position in the shielding matrix is ​​changed to 0; after the detection computer completes all pixel judgments, the shielding matrix is ​​obtained. The detection computer shields the pixels through the obtained shielding matrix. If the value of a certain pixel at the corresponding position of the shielding matrix is ​​1, the pixel works normally. If the value of the corresponding position is 0, the pixel is selected by closing the site selection circuit and closed to complete the shielding operation.

[0043] Preferably, the schematic diagram of the array pixel control circuit described in this embodiment is as follows: Figure 7As shown, the input signals are SWITCH, COL_CLOSE, ROW_CLOSE, COL_OPEN, ROW_OPEN, WLP, HV, VDD, VEX and VSS; the output signal is OUT; VDD, VSS and VEX are working voltages, VDD and VEX are high voltages, which may not be equal, and VSS is a low voltage; HV is connected to the photosensitive part of the SPAD pixel to receive the light signal, OUT is the output, and outputs the photon pulse; SWITCH is the full pixel switch, COL_CLOSE, ROW_C The four signals LOSE, COL_OPEN, and ROW_OPEN represent the row and column selection closure and row and column selection opening, respectively, which are controlled by the row closure bus, column closure bus, row opening bus, and column opening bus, respectively. Each pixel is selected by the coordinated transmission signal of the row and column buses; among them, the D flip-flop works normally when the RN signal is high, and Q is set low when it is low, and VDD is high; the COL_OPEN signal and the ROW_OPEN signal are connected to the CLK end of the D flip-flop through the AND gate, and the COL_CLOSE and ROW_CLOSE are connected through the NAND gate, and the output signal is then Through the AND gate and the SWITCH signal connection, the output is connected to the RN of the trigger, the D of the trigger is directly connected to VDD, and the output Q is connected to the GATE end of the quenching circuit. When it is high, the quenching circuit works normally, and the optical signal of the SPAD device enters the quenching circuit through HV. OUT outputs a photon pulse, which is received and counted by the subsequent register; when the pixel is normally exposed and photon counting is performed, RN is high and COL_OPEN and ROW_OPEN are both high, Q is high, and the pixel is selected to be turned on, corresponding to the normal exposure of the pixel in the time delay integration SPAD array. At this time, COL _CLOSE and ROW_CLOSE are both low, SWITCH is high; when the detection computer determines that the pixel is a bad pixel and shields it according to the shielding matrix, the pixel is selected by shutting down the row and column buses. At this time, the COL_CLOSE and ROW_CLOSE signals of the pixel are high, RN is low, Q is low, the quenching circuit no longer works normally, and has no response to the light signal. The pixel shielding is completed, and the shielded pixel no longer counts photons, but receives the signal of the previous level as the transfer signal is driven and directly passes the photon count value of the previous level to the next level transfer counter.

[0044] Preferably, Figure 8As shown, after completing the detection mode and shielding the pixels according to the shielding matrix, the time delay integration SPAD array described in this embodiment can work normally in the TDI mode. At this time, it is assumed that the last level circuit of the x-th row outputs the photon count value Q after completing the exposure. The correct count value can be obtained by recovering Q, thereby reducing the influence of bad pixels on the result; the photon count value Q passes through M levels of pixels in total, and it is assumed that N pixels are shielded for the count value. At this time, the x-th row in the shielding matrix corresponding to the SPAD array has N elements 0 and (MN) elements 1, and the output photon count value Q is the photon count value result obtained within (MN) exposure cycles; the detection computer performs mathematical calculations based on the photon count value Q and the number N of elements 0 in the row of the shielding matrix, Q r =Q / (MN)*M,Q r This is the photon count value obtained after the pixel array is shielded and repaired.

[0045] Compared with the single SPAD pixel bad pixel shielding technology, the SPAD pixel bad pixel shielding technology of the present invention combined with the time delay integration SPAD array can eliminate the influence of manufacturing pixel yield on the photon count value, thereby effectively reducing the influence of a certain level of bad pixel in the SPAD array on the photon count value of the entire level, greatly improving the effectiveness and stability of the SPAD array, so that it can be applied to more complex environmental scenarios.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting, shielding and restoring bad pixels of a time-delayed integration SPAD array, characterized in that: The steps include: Step 1: Detect the count value of each pixel in the time-delayed integration SPAD array working in the detection mode within an exposure period; Step 2: Output the count values ​​of all photons in sequence and determine whether the current pixel is a bad pixel based on the count value detection result and record the bad pixel position, obtain the shielding matrix from the bad pixel position, and shield the bad pixel through the driving circuit based on the shielding matrix; Step 3: When the SPAD array works in TDI mode, the last level of pixels outputs a photon count value after completing exposure, and the count value is restored based on the number of shielded pixels in the shielding matrix row where the count value is located.

2. The method for detecting, shielding and restoring bad pixels of a time-delayed integration SPAD array according to claim 1, characterized in that: The time-delayed integration SPAD array operates in a detection mode, at which time all pixels of the array are exposed and record the number of photons within one exposure cycle, and then all pixels are turned off and the count values ​​are transmitted backward one level at a time until all are transmitted. All transmitted count values ​​are sent to a detection computer for bad pixel judgment. If it is judged to be a bad pixel, it is recorded to obtain a shielding matrix.

3. The method for bad pixel detection, shielding and recovery of a time-delayed integration SPAD array according to claim 1, characterized in that: Each pixel in the time-delayed integration SPAD array has an independent switch control unit, which is selected by the row and column buses according to the shielding matrix. A configurable shutdown operation can be implemented at any position to complete the shielding. When the time-delayed integration SPAD array operates in TDI mode, the shielded pixel will transfer the count value of the previous level pixel to the next level pixel under the drive of the transfer signal.

4. The method for bad pixel detection, shielding and recovery of a time-delayed integration SPAD array according to claim 1, characterized in that: The switch control unit includes a logic gate and a D flip-flop, and the input signal of the switch control unit is composed of a row and column bus of an open pixel, a row and column bus of a closed pixel, and an array switch; when the array switch is turned on, all pixels enter the working mode in sequence under the selection of the open row and column bus, and when the detection computer completes the judgment and obtains the shielding matrix, the shielding row and column bus is closed according to the pixel selected by the shielding matrix.

5. The method for bad pixel detection, shielding and recovery of a time-delayed integration SPAD array according to claim 1, characterized in that: The time-delayed-integrated SPAD array is a multi-level TDI array.

6. The method for bad pixel detection, shielding and recovery of a time-delayed integration SPAD array according to claim 5, characterized in that: By detecting the count value of each pixel in each level of the TDI array, it is determined whether the pixel at that level is damaged. A shielding matrix is ​​generated based on the judgment result, and the damaged pixels are shut down and shielded through the control circuit according to the shielding matrix. The transfer counter in the shut-off pixel will directly transfer the photon count value of the previous level to the next level, and at the same time, the number of shielded pixels in each row in the shielding matrix is ​​counted. Finally, the photon output value of the last level circuit of each row is compensated according to the number of shielded pixels in the shielding matrix to obtain a normal photon count value.

7. The method for bad pixel detection, shielding and recovery of a time-delayed integration SPAD array according to claim 6, characterized in that: The TDI array comprises M×L columns of pixels, including M×1 output column pixels and (L-1) M×1 front-stage column pixels. The M×L pixels in the TDI array are detected, and the detection can be realized by a detection computer.

8. The method for bad pixel detection, shielding and recovery of a time-delayed integration SPAD array according to claim 7, characterized in that: After the detection computer reads out the photon count values ​​of all pixels in one exposure cycle, the detection computer determines whether the count value of each pixel is too high or too low, and obtains a shielding matrix.

9. The method for detecting, shielding and restoring bad pixels of a time-delayed integration SPAD array according to claim 8, characterized in that: The size of the shielding matrix is ​​M×L, and the elements are 1 or 0; if the count value is normal, the pixel is normal and the mark position is 1; if the count value is too high or too low, it is judged as a bad pixel and the mark position is 0; if a bad pixel appears in the xth row and yth column (x<=M, y<=L), the value of the (x, y) position in the shielding matrix is ​​changed to 0; the shielding matrix is ​​obtained after the detection computer completes all pixel judgments.

10. The method for detecting, shielding and restoring bad pixels of a time-delayed integration SPAD array according to claim 9, characterized in that: After completing the detection mode and shielding the pixels according to the shielding matrix, the time delay integration SPAD array can work normally in the TDI mode. At this time, it is assumed that the last level circuit of the x-th row outputs the photon count value Q after completing the exposure. The correct count value can be obtained by restoring Q, thereby reducing the influence of bad pixels on the result; the photon count value Q passes through M levels of pixels in total, and it is assumed that N pixels are shielded for the count value. At this time, the x-th row in the shielding matrix corresponding to the SPAD array has N elements 0 and (MN) elements 1, and the output photon count value Q is the photon count value result obtained within (MN) exposure cycles; the detection computer performs mathematical calculations based on the photon count value Q and the number N of elements 0 in the row of the shielding matrix, Q r =Q / (MN)*M,Q r This is the photon count value obtained after the pixel array is shielded and repaired.

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