A method for bad pixel detection, masking and recovery of a time delay integration SPAD array

Abstract

A kind of bad point detection, shielding and recovery method of time delay integration SPAD array, comprising the following steps: step one: the count value of each pixel in time delay integration SPAD array working in detection mode in an exposure period is detected;Step two: all the photon count values are output in turn and whether the current pixel is a bad point is judged according to the count value detection result and the bad point position is recorded, the shielding matrix is obtained from the bad point position, and the shielding of bad point pixel is realized according to the shielding matrix;Step three: when SPAD array works in TDI mode, the photon count value is output after the last stage pixel completes exposure, and the count value recovery is completed according to the number of shielding pixels in the row of shielding matrix where the count value is located.The present application combines SPAD pixel bad point shielding technology with time delay integration SPAD array, effectively reduces the influence of a certain stage bad point pixel on the whole stage photon count value through the use of shielding technology and recovery technology, greatly improves the effectiveness and stability of SPAD array.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of integrated circuits, in particular to a bad pixel detection, shielding and recovery method of a time delay integration SPAD array. BACKGROUND

[0002] In recent years, photoelectric detection type sensors have been widely used. Based on single photon avalanche diode detectors (SPAD), time delay integration (TDI) arrays have been developed. TDI chips based on SPAD arrays have the advantages of low power consumption and high definition when shooting fast-moving objects. Pixels using SPAD devices as light-sensitive units have the advantages of light sensitivity and fast response, but they may have the problem of high dark count or no response, resulting in high or low count values at this level, i.e. bad pixels. When a bad pixel in a multi-stage TDI SPAD array produces an incorrect count value, the incorrect count value will be transferred in each subsequent stage of the circuit by the transfer counter, and finally the array will output an incorrect count value. For a time delay integration SPAD array with a high number of stages, the photon count value of each row will go through many pixels, and it is more likely to encounter a bad pixel during the transfer of a row.

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

[0004] The shielding technology for pixels can be used in time delay integration SPAD arrays, and combined with a bad pixel recovery technology, to effectively reduce the impact of bad pixels in a multi-stage SPAD array on the count value. SUMMARY

[0005] The present application provides a bad pixel detection, shielding and recovery method for a time delay integration SPAD array to solve the defects in the prior art.

[0006] The present application is implemented by the following technical solutions:

[0007] A bad pixel detection, shielding and recovery method for a time delay integration SPAD array, comprising the following steps:

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

[0009] Step two: output all the photon counting values in sequence and determine whether the current pixel is a bad pixel according to the counting value detection result and record the bad pixel position, obtain the shielding matrix from the bad pixel position, and realize shielding of the bad pixel through the driving circuit according to the shielding matrix;

[0010] Step three: when the SPAD array works in the TDI mode, the last stage pixel outputs the photon counting value after completing exposure, and the counting value is recovered according to the number of shielding pixels in the row of the shielding matrix in which the counting value is located.

[0011] The bad pixel detection, shielding and recovery method of the time delay integration SPAD array as described above, the time delay integration SPAD array works in the detection mode, at this time all the pixels of the array record the number of photons in an exposure period, then all the pixels are turned off and the counting values are transferred back one by one until all the counting values are transmitted out, the transmitted counting values are sent to the detection computer for bad pixel judgment, and if it is judged as a bad pixel, it is recorded to obtain the shielding matrix.

[0012] The bad pixel detection, shielding and recovery method of the time delay integration SPAD array as described above, each pixel in the time delay integration SPAD array has an independent switch control unit, which is selected by the row and column bus according to the shielding matrix, and the configurable turn-off operation can be realized at any position to complete shielding, and when the time delay integration SPAD array works in the TDI mode, the shielded pixels will transfer the counting value of the previous stage pixel to the next stage pixel under the driving of the transfer signal.

[0013] The bad pixel detection, shielding and recovery method of the time delay integration SPAD array as described above, the switch control unit includes a logic gate and a D flip-flop, the input signal of the switch control unit is composed of the row and column buses of the opened pixels, the row and column buses of the turned-off pixels and the array switch; in the state that the array switch is opened, all the pixels enter the working mode under the selection of the opened row and column buses, and when the detection computer completes the judgment to obtain the shielding matrix, the shielding row and column buses select the pixels to be closed according to the shielding matrix

[0014] The bad pixel detection, shielding and recovery method of the time delay integration SPAD array as described above, the time delay integration SPAD array belongs to a multi-stage TDI array.

[0015] The bad pixel detection, shielding and recovery method of the time delay integration SPAD array as described above judges whether the pixel of each stage of the TDI array is damaged by detecting the count value of each pixel, generates a shielding matrix according to the judgment result, and shields the damaged pixel through the control circuit according to the shielding matrix. The transfer counter of the closed pixel directly transfers the photon count value of the previous stage to the next stage, and the number of shielding pixels in each row of the shielding matrix is counted. Finally, the normal photon count value is obtained by compensating the photon output value of the last stage circuit in each row according to the number of shielding pixels in the row of the shielding matrix.

[0016] The bad pixel detection, shielding and recovery method of the time delay integration SPAD array as described above, the TDI array contains MxL column pixels, including Mx1 output column pixels and (L-1) Mx1 previous stage column pixels, and the MxL pixels in the TDI array are detected, which can be realized by a detection computer.

[0017] The bad pixel detection, shielding and recovery method of the time delay integration SPAD array as described above, after the detection computer reads out the photon count value of all pixels in an exposure period, the detection computer judges whether the count value of each pixel is too high or too low, and obtains a shielding matrix.

[0018] The bad pixel detection, shielding and recovery method of the time delay integration SPAD array as described above, the shielding matrix has a size of MxL and elements of 1 or 0; if the count value is normal, the pixel is normal and the position is marked as 1; if the count value is too high or too low, it is judged that a bad pixel appears and the position is marked as 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 detection computer obtains the shielding matrix after completing the judgment of all pixels.

[0019] The bad pixel detection, shielding and recovery method of the time delay integration SPAD array as described above, after the detection mode is completed and the pixel is shielded according to the shielding matrix, the time delay integration SPAD array can work in the TDI mode for normal use. At this time, the photon count value Q output by the last stage circuit in the xth row after completing exposure is set. The correct count value can be obtained by recovering Q, thereby reducing the influence of the bad pixel on the result. The photon count value Q passes through M stages of pixels. It is assumed that N pixels have count value shielding. At this time, there are N elements 0 and (M-N) elements 1 in the xth row of the shielding matrix corresponding to the SPAD array. The output photon count value Q is the photon count value obtained in (M-N) exposure periods. According to the number N of elements 0 in the row of the shielding matrix, the detection computer performs mathematical calculation on the photon count value Q. r =Q / (M-N)*M, Qr The photon counting value obtained after the pixel array is shielded and repaired.

[0020] The advantage of the present application is that the present application is based on the existing SPAD pixel bad point shielding technology, which combines the technology with the time delay integration SPAD array, and effectively reduces the influence of a certain level of bad pixel in the SPAD array on the whole level of photon counting value through the shielding technology and the recovery technology, greatly improves the effectiveness and stability of the SPAD array, and makes it can be applied to more complex scenes. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0022] Figure 1 It is a general flowchart of the bad point detection, shielding and recovery method suitable for the time delay integration SPAD array proposed by the present application;

[0023] Figure 2 It is a structure diagram of the time delay integration SPAD array of the present application;

[0024] Figure 3 It is a schematic diagram of the time delay integration SPAD array of the present application;

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

[0026] Figure 5 It is a process diagram of the detection computer of the present application according to the counting value to obtain the shielding matrix;

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

[0028] Figure 7 It is a schematic diagram of the bad point detection, shielding and recovery method of the time delay integration SPAD array of the present application;

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

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only 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 making creative efforts shall fall within the scope of protection of the present invention.

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

[0032] Step 1: Time delay integration SPAD array (its structure is as follows) working in 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 layer structure; the upper layer structure is mainly the pixel photosensitive part mainly composed of SPAD devices, and the lower layer structure is the pixel control circuit part; the upper layer SPAD devices are closely arranged to form a complete photosensitive layer, and its opening and closing are controlled by the lower layer control circuit; the lower layer control circuit layer contains the control circuit of all pixels, wherein each control circuit contains a driving circuit part, and 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) in the detection of 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. Calculate the shielding matrix based on the bad pixel position and shield the bad pixel through the driving circuit according to the shielding matrix.

[0034] Step 3: When the SPAD array operates 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 operates in detection mode. At this time, all pixels in the array are exposed and record the number of photons within one exposure cycle. Then all pixels are turned off and the count values ​​are transmitted 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 at the same time 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. The input signal of the switch control unit is composed of a row and column bus of a pixel that is turned on, a row and column bus that is turned off, and an array switch. When the array switch is turned on, all pixels enter the working mode in sequence under the selection of the turned-on row and column bus. When the detection computer completes the judgment and obtains the shielding matrix, the shielding row and column bus is selected according to the shielding matrix and the pixel is turned off.

[0038] Preferably, the time delay integration 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 each 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 the control circuit according to the shielding matrix. The transfer counter in the shut-off pixel directly transfers the photon count value of the previous level to the next level, and at the same time 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 includes 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, the detection computer described in this embodiment reads out the photon count values ​​of all pixels in one exposure period, and then 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 the embodiment is MxL, and the elements are 1 or 0; if the count value is normal, the pixel is normal, and the position is marked as 1; if the count value is too high or too low, it is judged that a bad point appears, and the position is marked as 0; if a bad point 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 detection computer obtains the shielding matrix after completing the judgment of all pixels. The detection computer shields the pixels through the obtained shielding matrix; if the value of a certain pixel in 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 to be turned off by turning off the addressing circuit, and the shielding operation is completed.

[0043] Preferably, the schematic diagram of the array pixel control circuit described in the embodiment is as shown in Figure 7As shown, the input signals include 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 can be unequal, and VSS is a low voltage; HV is connected to the light-sensing part of the SPAD pixel and used to receive a light signal; OUT is the output of a photon pulse; SWITCH is a full-pixel switch; COL_CLOSE and ROW_CLOSE are signals for row and column selection closing, and COL_OPEN and ROW_OPEN are signals for row and column selection opening, which are controlled by the row closing bus, the column closing bus, the row opening bus and the column opening bus, respectively, and are transmitted by the cooperation of the row and column buses to select each pixel; the D flip-flop normally works when the RN signal is high, and Q is low when the RN signal is low, and VDD is high; the COL_OPEN signal and the ROW_OPEN signal are connected to the D flip-flop CLK end through an AND gate, the COL_CLOSE and the ROW_CLOSE are connected through an NAND gate, the output signal is connected to the SWITCH signal through an AND gate, the output is connected to the RN of the flip-flop, the D of the flip-flop is directly connected to VDD, and the output Q is connected to the GATE end of the quenching circuit, when the GATE end is high, the quenching circuit normally works, the light 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 the photon counting is performed, RN is high, COL_OPEN and ROW_OPEN are high, and Q is high, at this time, the pixel is selected to be turned on, and the normal exposure of the pixel in the time delay integration SPAD array is performed, at this time, COL_CLOSE and ROW_CLOSE are low, and SWITCH is high; when the detection computer judges that the pixel is a bad pixel and performs a shielding operation according to the shielding matrix, the pixel is selected through the row and column closing buses, at this time, the pixel COL_CLOSE and ROW_CLOSE signals are high, RN is low, Q is low, the quenching circuit no longer normally works, and the light signal has no response, the pixel shielding is completed, the shielded pixel no longer performs photon counting, but receives the signal of the previous stage and directly transmits the photon counting value of the previous stage to the next stage transfer counter.

[0044] Preferably, as Figure 8As shown, after the detection mode is completed and the pixels are shielded according to the shielding matrix, the time delay integration SPAD array in the embodiment can work in the TDI mode for normal use, at this time, the last stage circuit of the xth row outputs a photon count value Q after completing exposure, and the correct count value can be obtained by performing recovery processing on Q, thereby reducing the influence of bad points on the result; the photon count value Q is subjected to M-stage pixels, and it is assumed that N pixels perform count value shielding, at this time, the shielding matrix corresponding to the SPAD array has N elements 0 and (M-N) elements 1 in the xth row, and the output photon count value Q is the photon count value result obtained in (M-N) exposure periods; the detection computer performs mathematical calculation according to the photon count value Q and the number N of elements 0 in the row of the shielding matrix, Q r = Q / (M-N)*M, Q r That is, the photon count value obtained after the pixel array is shielded and repaired.

[0045] Compared with the single SPAD pixel bad point shielding technology, the SPAD pixel bad point shielding technology combined with the time delay integration SPAD array can eliminate the influence of the manufacturing pixel yield on the photon count value, thereby effectively reducing the influence of a bad point pixel in the SPAD array on the whole-stage photon count value, greatly improving the effectiveness and stability of the SPAD array, and enabling it to be applied to more complex scenes.

[0046] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for bad pixel detection, masking and recovery of a time delay integration SPAD array, characterized in that: It comprises the following steps: Step one: detecting the count value of each pixel in the time delay integration SPAD array working in the detection mode within an exposure period; Step two: outputting the count value of all photons in turn and judging whether the current pixel is a bad pixel according to the detection result of the count value and recording the position of the bad pixel, obtaining the shielding matrix from the position of the bad pixel, and shielding the bad pixel through the driving circuit according to the shielding matrix; Step three: when the SPAD array works in the TDI mode, the last stage pixel outputs the photon count value after completing exposure, and the count value is recovered according to the number of shielding pixels in the row of the shielding matrix in which the count value is located. The size of the shielding matrix is The element is 1 or 0; if the count value is normal, the pixel is normal, and the position is marked as 1; if the count value is too high or too low, it is judged that a bad point appears, and the position is marked as 0; if the first row and the first column have a bad point (x<=M, y<=L), the shielding matrix is changed to 0 in the position; after the detection computer completes all pixel judgments, the shielding matrix is obtained. ​ After the detection mode is completed and the pixels are shielded according to the shielding matrix, the time delay integration SPAD array can work in the TDI mode for normal use, at this time, the last stage circuit of the xth row outputs a photon count value Q after completing exposure, and the correct count value can be obtained by performing recovery processing on Q, thereby reducing the influence of bad points on the result; the photon count value Q is subjected to M stages of pixels, and it is assumed that N pixels perform count value shielding, at this time, the shielding matrix corresponding to the SPAD array has N elements 0 and (M-N) elements 1 in the xth row, and the output photon count value Q is the photon count value result obtained in (M-N) exposure periods; the detection computer performs mathematical calculation according to the photon count value Q and the number N of elements 0 in the row of the shielding matrix, =Q / (M-N)*M, that is, the photon count value obtained after the pixel array is shielded and repaired.

2. The method of bad pixel detection, masking and recovery of a time delay integration SPAD array according to claim 1, wherein: The time delay integration SPAD array works in the detection mode, at this time, all pixels in the array record the number of photons within an exposure period, then all pixels are turned off and the count value is transferred back stage by stage until it is completely transmitted out, and the completely transmitted count value is sent to the detection computer for bad pixel judgment, and if it is judged as a bad pixel, it is recorded to obtain the shielding matrix.

3. The method of bad pixel detection, masking and recovery of a time delay integration SPAD array according to claim 1, wherein: Each pixel in the time delay integration SPAD array has an independent switch control unit, which is selected by the row and column bus according to the shielding matrix, so that configurable turn-off operation can be realized at any position to complete shielding, and when the time delay integration SPAD array works in the TDI mode, the count value of the upper stage pixel is transferred to the lower stage pixel under the driving of the transfer signal.

4. The method of bad pixel detection, masking and recovery of a time delay integration SPAD array according to claim 3, wherein: The switch control unit comprises a logic gate and a D flip-flop, and the input signal of the switch control unit is composed of the row and column buses of the opened pixel, the row and column buses of the turned-off pixel, and the array switch; in the state that the array switch is opened, all pixels enter the working mode under the selection of the opened row and column buses, and when the detection computer completes the judgment to obtain the shielding matrix, the shielding row and column buses select the pixel to be closed according to the shielding matrix.

5. The method of bad pixel detection, masking and recovery of a time delay integration SPAD array according to claim 1, wherein: The time delay integration SPAD array belongs to a multi-stage TDI array.

6. The method of bad pixel detection, masking and recovery of a time delay integration SPAD array according to claim 5, wherein: By detecting the count value of each pixel in each stage of the TDI array to judge whether the pixel is damaged, a shielding matrix is generated according to the judgment result, and the damaged pixel is turned off and shielded through the control circuit according to the shielding matrix, the transfer counter in the turned-off pixel directly transfers the photon count value of the upper stage to the lower stage, the number of shielding pixels in each row of the shielding matrix is counted, and finally the photon output value of each row in the last stage circuit is compensated according to the number of shielding pixels in the row of the shielding matrix to obtain the normal photon count value.

7. The method of bad pixel detection, masking and recovery of a time delay integration SPAD array according to claim 6, wherein: The TDI array includes Column pixels include Output column pixels and ) pixels Preceding column pixels detect pixels in the TDI array, which can be implemented by a detection computer.

8. The method of bad pixel detection, masking and recovery of a time delay integration SPAD array according to claim 7, wherein: The detection computer judges whether the count value of each pixel is too high or too low after reading out the photon count value of all pixels within an exposure period, and obtains the shielding matrix.

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