Implementation method of pulse camera based on SPAD array

Abstract

The invention discloses a pulse camera implementation method based on an SPAD array. The pulse camera implementation method comprises the following steps: step 1, converting a pulse signal which is output by SPAD array pixels and represents photons into an n-photon pulse signal which represents that n photons are detected within a certain time through a digital logic system; wherein n is an integer greater than or equal to 1; 2, cyclically reading the n-photon pulse signals of each pixel in the row of pixels in sequence according to a preset reading time sequence to obtain an n-photon pulse signal sequence of each pixel; and step 3, according to the relationship among n photon pulse signals in the n photon pulse sequence output by each pixel, deducing the light intensity, and completing the detection function of the pulse camera. According to the invention, the problems that the SPAD pulse camera adapts to different scenes and the signal to noise ratio is low can be solved, so that the SPAD pulse camera can be widely popularized and applied.

Description

Technical Field

[0001] The invention belongs to the field of pulse cameras, in particular to a method for realizing a pulse camera based on a SPAD array. Background Art

[0002] Pulse cameras based on pulse imaging theory have great potential in the fields of high-speed imaging, target tracking, and intelligent imaging based on pulse neural networks. Pulse cameras capture photons through photosensitive devices, and generate pulses when the accumulated photons reach the set threshold. Based on this, the light intensity at any time can be reconstructed, thereby realizing continuous high-speed imaging. The existing pulse camera imaging chip based on CIS uses a comparator for threshold judgment, consumes a large number of chips, and has limited detection sensitivity. Single-photon avalanche diode (SPAD) is a photoelectric detection device with the characteristics of fast response and high gain. When SPAD detects a photon input, it outputs a pulse signal under the joint action of the quenching circuit. Based on the SPAD device, a pulse stream for pulse imaging can be directly output to complete the function of the pulse camera. However, due to the different response capabilities to photons of different background light intensities and the low signal-to-noise ratio of only recording a single photon, a pulse camera implementation method suitable for SPAD is needed to solve the problem of SPAD pulse camera adapting to different scenes and low signal-to-noise ratio. Summary of the invention

[0003] The present invention provides a method for realizing a pulse camera based on a SPAD array, so as to solve the defects in the prior art.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for realizing a pulse camera based on a SPAD array comprises the following steps:

[0006] Step 1: Convert the pulse signal representing the photon output by the SPAD array pixel into an n-photon pulse signal representing n photons detected within a certain period of time through a digital logic system; where n is an integer greater than or equal to 1;

[0007] Step 2: cyclically read out the n-photon pulse signal of each pixel in a row of pixels in sequence according to a preset readout timing to obtain a sequence of n-photon pulse signals of each pixel;

[0008] Step 3: The relationship between the n-photon pulse signals in the n-photon pulse sequence output by each pixel is used to deduce the light intensity and complete the pulse camera detection function.

[0009] In the above-mentioned method for realizing a pulse camera based on a SPAD array, the digital logic system includes a photon counting module, a counting comparison module, and a counting reset module.

[0010] In the above-mentioned method for realizing a pulse camera based on a SPAD array, the photon counting module is used to accumulate and count the photon signals output by the pixels of the SPAD photon detector.

[0011] In the above-mentioned method for implementing a pulse camera based on a SPAD array, the counting comparison module is used to compare the photon counting value output by the photon counting module with a set threshold value n, and when the cumulative counting value of the photon counting module reaches the set threshold value n, an n-photon pulse signal is output.

[0012] In the above-mentioned method for implementing a pulse camera based on a SPAD array, the counting reset module is used to reset the photon counting module according to the n-photon pulse signal output by the counting comparison module.

[0013] In the above-mentioned method for realizing a pulse camera based on a SPAD array, the readout timing in step 2 outputs the n-photon pulse signal output by the digital logic system inside each pixel of the pixel array in a timing sequence.

[0014] In the above-mentioned method for realizing a pulse camera based on a SPAD array, in step three, a grayscale image expressing light intensity is reconstructed by a cumulative counting method or a pulse interval method.

[0015] In the above-mentioned method for realizing a pulse camera based on a SPAD array, the specific operation of the cumulative counting method is: cumulatively counting the number of pulses in the pulse signal sequence output within a period of time, and obtaining the grayscale value representing the light intensity information detected by the pixel during this period of time.

[0016] As described above, a method for implementing a pulse camera based on a SPAD array, the specific operation of the pulse interval method is: counting the readout period between two pulses output by the pixel to obtain the time required to accumulate n photons, and the inverse of the light intensity accumulation time is the grayscale value corresponding to that moment.

[0017] As described above, a method for realizing a pulse camera based on a SPAD array, the SPAD array is composed of M columns and N rows of pixel units, and the M pixels in each row are connected in sequence based on the readout timing, and the output of each pixel data in the row is completed at the end of each row; the M pixels in each row contain a readout shift register connected in sequence, and under the control of a unified readout signal and a readout clock, the readout of the entire row of pixel data is realized; the pixel unit includes a SPAD device, a quenching circuit, a photon counting circuit, a comparison latch circuit, a counting reset circuit, a latch reset circuit, and a readout shift register.

[0018] In the above-mentioned method for realizing a pulse camera based on a SPAD array, the photon counting circuit is composed of an n-bit D flip-flop, and the output n-bit binary value represents the number of digital pulses output by the recorded SPAD array; the reset of the counter is controlled by the counting reset circuit.

[0019] In the method for realizing a pulse camera based on a SPAD array as described above, the comparison latch circuit is composed of a digital comparator and a D flip-flop; the comparison latch circuit receives an external m-bit binary code value as input to determine the photon threshold; when the photon counting circuit outputs a count value equal to the set photon threshold, it outputs a high level "1" and is latched by the latch; when the photon counting circuit outputs a count value that does not reach the set photon threshold, the output remains at a low level "0" and the latch does not respond.

[0020] In the above-mentioned method for realizing a pulse camera based on a SPAD array, the latch reset circuit is used to reset the D flip-flop in the comparison latch circuit according to the triggering of the readout signal; the reset method ensures that the counting function and the comparison function of the circuit are not affected by the subsequent readout timing and can work normally.

[0021] In the above-mentioned method for realizing a pulse camera based on a SPAD array, the counting reset circuit is used to reset the counter in the photon counting circuit according to the output of the comparison latch circuit.

[0022] In the above-mentioned method for realizing a pulse camera based on a SPAD array, the readout shift register includes a two-to-one selector and a D flip-flop; the two-to-one selector is controlled by the readout signal to control the data in the current pixel or the previous pixel data to enter the D flip-flop; the output end of the D flip-flop is connected to the two-to-one selector of the next pixel; the D flip-flop completes the transfer and readout of data between pixels under the control of the readout clock.

[0023] The advantages of the present invention are that the present invention can solve the problem that the SPAD pulse camera is adaptable to different scenes and has a low signal-to-noise ratio, thereby enabling it to be widely promoted and applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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.

[0025] Figure 1 It is a schematic diagram of the SPAD array structure of the present invention;

[0026] Figure 2 The pixel output pulse sequence in the present invention reconstructs the light intensity by using the cumulative counting method (Figure a) and the pulse interval method (Figure b) to reconstruct the grayscale image expressing the light intensity;

[0027] Figure 3 It is a schematic diagram of the circuit structure in a single pixel of the present invention. DETAILED DESCRIPTION

[0028] 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.

[0029] A method for realizing a pulse camera based on a SPAD array comprises the following steps:

[0030] Step 1: Convert the pulse signal representing the photon output by the SPAD array pixel into an n-photon pulse signal representing n photons detected within a certain period of time through a digital logic system; where n is an integer greater than or equal to 1;

[0031] Step 2: cyclically read out the n-photon pulse signal of each pixel in a row of pixels in sequence according to a preset readout timing to obtain a sequence of n-photon pulse signals of each pixel;

[0032] Step 3: The relationship between the n-photon pulse signals in the n-photon pulse sequence output by each pixel is used to deduce the light intensity and complete the pulse camera detection function.

[0033] Preferably, the digital logic system described in this embodiment includes a photon counting module, a counting comparison module, and a counting reset module.

[0034] Preferably, the photon counting module described in this embodiment is used to accumulate and count photon signals output by pixels of the SPAD photon detector.

[0035] Preferably, the counting comparison module described in this embodiment is used to compare the photon counting value output by the photon counting module with a set threshold value n. When the cumulative counting value of the photon counting module reaches the set threshold value n, an n-photon pulse signal is output; the generation of the n-photon pulse signal is determined by the set threshold value n, and is generated when the SPAD array detects n photons; the set threshold value n is a positive integer, which can be selected according to the scene light intensity and the array readout rate.

[0036] Preferably, the counting reset module described in this embodiment is used to reset the photon counting module according to the n-photon pulse signal output by the counting comparison module.

[0037] Preferably, the readout timing in step 2 described in this embodiment outputs the n-photon pulse signals output by the digital logic system inside each pixel of the pixel array in a timing sequence.

[0038] Preferably, each row of the pixel array described in this embodiment is composed of M pixels, each pixel is connected in sequence, and the last pixel realizes external data output.

[0039] Preferably, Figure 1 As shown, during the triggering period of the readout signal, the digital logic system described in this embodiment transfers and reads out the n-photon pulse signals generated by the digital logic system inside each pixel of a row of M pixels based on the readout clock.

[0040] Preferably, the readout clock described in this embodiment is connected to each pixel to control the signals in each pixel to be transferred and read out in sequence, and each clock cycle completes the reading of one pixel data, that is, M clock cycles are required to read out the row of data.

[0041] Preferably, the readout signal described in this embodiment completes synchronous storage of internal data of each pixel during the non-triggering period, and completes sequential transfer and reading of pixel data of the row during the triggering period of the readout signal.

[0042] Preferably, each triggering time of the readout signal described in this embodiment lasts for M clock cycles, and each non-triggering event lasts for one clock cycle;

[0043] Preferably, the SPAD array described in this embodiment requires M+1 clock cycles for one readout;

[0044] Preferably, in the present embodiment, the data read out once for each row of pixels is an M data sequence consisting of M "0"s and "1"s. After the same row of pixels is read out in multiple uninterrupted cycles, multiple M data sequences are formed. The data combination at the same position of each M data sequence forms an n-photon pulse signal sequence of the pixel corresponding to that position.

[0045] Preferably, in this embodiment, the threshold value is set to 4; the first row represents the photon flow. Due to the randomness of the photon behavior and the change of light intensity, the photon pulse shows a non-equidistant pulse sequence; the second row represents the SPAD detector pixel output photon signal. Under the action of the SPAD and the quenching circuit, a pulse signal is output each time a photon is detected; the third row represents the cumulative counting of the photon signal by the photon counting module. When the photon count value reaches 4, the digital logic resets the photon counting module and restarts a new photon counting; the fourth row represents n-photon pulses. When the photon count value reaches 4, the n-photon pulse signal is pulled up to a high level; when the rising edge of the readout signal arrives, the n-photon pulse signal is reset to a low level; the fifth row represents the readout signal. The high level of the readout signal lasts for M readout clock cycles, and the low level of the readout signal lasts for 1 readout clock cycle; during the high level period, the n-photon pulses of each pixel in the entire row are transferred and read out in turn, and during the low level period, preparations are made for the next readout cycle. The sixth row represents the pixel readout pulse signal. Under the control of the readout signal, the n-photon pulse signal is read out and converted into a "01" signal sequence according to the readout signal frequency; when the rising edge of the readout signal arrives, if the n-photon pulse signal is high, "1" is output; if the n-photon pulse signal is low, "0" is output.

[0046] Preferably, Figure 2 As shown, in step three of this embodiment, a grayscale image expressing light intensity is reconstructed through a cumulative counting method or a pulse interval method.

[0047] Preferably, the specific operation of the cumulative counting method described in this embodiment is: cumulatively count the number of pulses in the pulse signal sequence output within a period of time to obtain the grayscale value representing the light intensity information detected by the pixel during this period of time; in this embodiment, the cumulative period is 4, that is, every four signals cumulatively output the grayscale value of the time period (4*readout period), and the pulse signal sequence is converted into a 4-value grayscale sequence.

[0048] Preferably, the specific operation of the pulse interval method described in this embodiment is: counting the readout period between two pulses output by the pixel to obtain the time required to accumulate n photons, and the inverse of the light intensity accumulation time is the grayscale value corresponding to that moment; that is, the interval between each "1" and the previous "1"; the light intensity at that moment is inversely proportional to the pulse interval, and the grayscale value between the two pulses can be obtained using this pulse interval.

[0049] Preferably, the SPAD array described in this embodiment is composed of M columns and N rows of pixel units, each row of M pixels is connected in sequence based on the readout timing, and the output of each pixel data in the row is completed at the end of each row; each row of M pixels contains a readout shift register connected in sequence, and under the control of a unified readout signal and a readout clock, the pixel data of the entire row is read out; the pixel unit (circuit structure diagram as shown in FIG. Figure 3 The device includes a SPAD device, a quenching circuit, a photon counting circuit, a comparison latch circuit, a counting reset circuit, a latch reset circuit, and a readout shift register.

[0050] Preferably, the photon counting circuit described in this embodiment is composed of an n-bit D flip-flop, and outputs an n-bit binary value representing the number of digital pulses output by the recorded SPAD array; the reset of the counter is controlled by the counting reset circuit.

[0051] Preferably, the comparison latch circuit described in this embodiment is composed of a digital comparator and a D flip-flop; the comparison latch circuit receives an external m-bit binary code value as input to determine the photon threshold; when the photon counting circuit outputs a count value equal to the set photon threshold, it outputs a high level "1" and is latched by the latch; when the photon counting circuit outputs a count value that does not reach the set photon threshold, the output remains at a low level "0" and the latch does not respond.

[0052] Preferably, the latch reset circuit described in this embodiment is used to reset the D flip-flop in the comparison latch circuit according to the triggering of the read signal; the reset method ensures that the circuit counting function and the comparison function are not affected by the subsequent read timing and can work normally.

[0053] Preferably, the counting reset circuit described in this embodiment is used to reset the counter in the photon counting circuit according to the output of the comparison latch circuit.

[0054] Preferably, the readout shift register described in this embodiment includes a two-to-one selector and a D flip-flop; the two-to-one selector is controlled by the readout signal to control the data in the current pixel or the previous pixel data to enter the D flip-flop; the output end of the D flip-flop is connected to the two-to-one selector of the next pixel; the D flip-flop completes the transfer and readout of data between pixels under the control of the readout clock.

[0055] 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 realizing a pulse camera based on a SPAD array, characterized in that: The steps include: Step 1: Convert the pulse signal representing the photon output by the SPAD array pixel into an n-photon pulse signal representing n photons detected within a certain period of time through a digital logic system; where n is an integer greater than or equal to 1; Step 2: cyclically read out the n-photon pulse signal of each pixel in a row of pixels in sequence according to a preset readout timing to obtain a sequence of n-photon pulse signals of each pixel; Step 3: The relationship between the n-photon pulse signals in the n-photon pulse sequence output by each pixel is used to deduce the light intensity and complete the pulse camera detection function.

2. A method for realizing a pulse camera based on a SPAD array according to claim 1, characterized in that: The digital logic system includes a photon counting module, a counting comparison module, and a counting reset module; The photon counting module is used to accumulate and count the photon signals output by the pixels of the SPAD photon detector; The counting comparison module is used to compare the photon counting value output by the photon counting module with a set threshold value n, and when the cumulative counting value of the photon counting module reaches the set threshold value n, an n-photon pulse signal is output; The counting reset module is used to reset the photon counting module according to the n-photon pulse signal output by the counting comparison module.

3. The method for realizing a pulse camera based on a SPAD array according to claim 1, characterized in that: The readout timing in step 2 outputs the n-photon pulse signals output by the digital logic system inside each pixel of the pixel array in a timing sequence.

4. The method for realizing a pulse camera based on a SPAD array according to claim 1, characterized in that: In the step 3, a grayscale image expressing light intensity is reconstructed by a cumulative counting method or a pulse interval method; The specific operation of the cumulative counting method is: cumulatively counting the number of pulses of the pulse signal sequence output within a period of time to obtain the gray value representing the light intensity information detected by the pixel during the period of time; The specific operation of the pulse interval method is: count the readout period between two pulses output by the pixel to obtain the time required to accumulate n photons, and the reciprocal of the light intensity accumulation time is the grayscale value corresponding to that moment.

5. The method for realizing a pulse camera based on a SPAD array according to claim 1, characterized in that: The SPAD array is composed of M columns and N rows of pixel units. Based on the readout timing, the M pixels in each row are connected in sequence, and the output of the pixel data in the row is completed at the end of each row; the M pixels in each row contain readout shift registers that are connected in sequence, and under the control of a unified readout signal and a readout clock, the readout of the entire row of pixel data is realized; the pixel unit includes a SPAD device, a quenching circuit, a photon counting circuit, a comparison latch circuit, a counting reset circuit, a latch reset circuit, and a readout shift register.

6. The method for realizing a pulse camera based on a SPAD array according to claim 5, characterized in that: The photon counting circuit is composed of an n-bit D flip-flop, and outputs an n-bit binary value representing the number of digital pulses output by the recorded SPAD array; the reset of the counter is controlled by the counting reset circuit.

7. The method for realizing a pulse camera based on a SPAD array according to claim 5, characterized in that: The comparison latch circuit is composed of a digital comparator and a D flip-flop; the comparison latch circuit receives an external m-bit binary code value as input to determine the photon threshold; when the photon counting circuit outputs a count value that is equal to the set photon threshold, it outputs a high level "1" and is latched by a latch; when the photon counting circuit outputs a count value that does not reach the set photon threshold, it outputs a low level "0" and the latch does not respond.

8. The method for realizing a pulse camera based on a SPAD array according to claim 7, characterized in that: The latch reset circuit is used to reset the D flip-flop in the comparison latch circuit according to the triggering of the read signal; the reset method ensures that the counting function and the comparison function of the circuit are not affected by the subsequent read timing and can work normally.

9. The method for realizing a pulse camera based on a SPAD array according to claim 5, characterized in that: The counting reset circuit is used to reset the counter in the photon counting circuit according to the output of the comparison latch circuit.

10. The method for realizing a pulse camera based on a SPAD array according to claim 5, characterized in that: The readout shift register includes a two-choice selector and a D flip-flop; the two-choice selector is controlled by the readout signal to control the data in the current pixel or the previous pixel data to enter the D flip-flop; the output end of the D flip-flop is connected to the two-choice selector of the next pixel; The D flip-flop completes the transfer and readout of data between pixels under the control of the readout clock.

Images