Time-of-flight information extraction method and system

Abstract

The application discloses a time-of-flight information extraction method and system, comprising the following steps: resetting the counting values of a plurality of analog counters to initial counting values, each analog counter is provided with at least one counting capacitor, and the counting capacitor is used for obtaining the counting value; a histogram generation circuit receives a plurality of time-of-flight code words from a time-to-digital converter; in a detection time, the analog counter corresponding to the digital address of the received plurality of time-of-flight code words is selected, and the counting value of the selected analog counter is increased by a minimum counting step; the time-of-flight histogram is filtered according to the different numbers of counting capacitors corresponding to different analog counters and the different charge amounts of the counting capacitors; and the filtered time-of-flight histogram is subjected to peak detection to extract time-of-flight information. The application can significantly reduce the resource consumption of the circuit.

Description

Technical Field

[0001] This invention belongs to the field of lidar ranging technology, specifically relating to a method and system for extracting time-of-flight information. Background Technology

[0002] Time-of-flight (ToF) is a lidar ranging and imaging method. A laser source emits a laser beam onto the object in the field of view. After the light beam hits the object, it is reflected and received by a photoelectric sensor. The time of flight of the light can be measured directly or indirectly.

[0003] In most 3D imaging applications, to reduce time-of-flight errors and achieve effective distance detection, the single-photon avalanche diode (SPAD) in the photoelectric sensor needs to perform many detections. By performing histogram statistics on the results of multiple detections, a time-of-flight histogram is generated. Utilizing the correlation of time-of-flight, the time-of-flight information corresponding to the echo can be found in the time-of-flight histogram. However, for outdoor high-background-light scenes, the time-of-flight histogram contains effective triggering information and ineffective noise information, requiring filtering to extract effective time-of-flight information under low signal-to-noise ratio conditions.

[0004] In existing technologies, the generation of time-of-flight histograms is generally based on the digital domain, using methods such as static random access memory (SRAM) or parallelized digital counters for statistical analysis. Then, a finite impulse response (FIR) filter is used to filter the time-of-flight histogram. Finally, after filtering, algorithms such as the centroid weighting method are used to extract effective time-of-flight information. However, the generation of time-of-flight histograms based on the digital domain relies on SRAM or parallelized digital counters, consuming significant area and power. Furthermore, the filtering operation and time-of-flight algorithm extraction scheme have high computational requirements, consume substantial digital hardware resources, and are not easily integrated with analog counting schemes based on the analog domain.

[0005] Therefore, there is an urgent need to propose a method for generating time-of-flight histograms based on the analog domain, as well as a method for extracting time-of-flight information, to reduce the area of ​​the processing circuit and the power consumption. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, this invention provides a method and system for extracting time-of-flight information. The technical problem to be solved by this invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a method for extracting flight time information, comprising:

[0008] The count values ​​of multiple analog counters are reset to the initial count values. Each analog counter is equipped with at least one counting capacitor, which is used to acquire the count value. Different analog counters correspond to different histogram bins in the time-of-flight histogram.

[0009] The histogram generation circuit receives multiple time-of-flight codewords from a time-to-digital converter; wherein the time-to-digital converter has an input coupled to a single-photon avalanche diode;

[0010] During the detection time, for the multiple received time-of-flight codewords, an analog counter corresponding to the digital address is selected, and the count value of the selected analog counter is increased by a minimum counting step. At the end of the detection time, each analog counter obtains its final count value, and a time-of-flight histogram is generated based on the final count values ​​of all analog counters.

[0011] The flight time histogram is filtered based on the different number of counting capacitors or the different charge amounts of the counting capacitors set for different analog counters.

[0012] Peak detection is performed on the filtered time-of-flight histogram to extract time-of-flight information.

[0013] In a second aspect, the present invention provides a flight time information extraction system, comprising:

[0014] Multiple single-photon avalanche diodes are configured to generate SPAD events;

[0015] Multiple time-to-digital converters are coupled to multiple single-photon avalanche diodes; wherein each time-to-digital converter is configured to generate multiple time-of-flight codewords based on SPAD events generated by the single-photon avalanche diodes;

[0016] A histogram generation circuit, coupled to multiple time-to-digital converters; wherein the histogram generation circuit includes:

[0017] The addressing logic unit includes multiple outputs and inputs configured to receive multiple time-of-flight codewords from the time-to-digital converter; and,

[0018] Multiple analog counters, including inputs coupled to multiple outputs of the addressing logic unit; each analog counter is provided with at least one counting capacitor;

[0019] The addressing logic unit is configured to select the analog counter corresponding to the digital address based on multiple received time-of-flight codewords during the probe time, and to enable the input of the selected analog counter; wherein, the selected analog counter is configured to increment the count value of the selected analog counter by a minimum counting step when the input of the selected analog counter is enabled; wherein, the counting capacitor of each analog counter is configured to have a final voltage at the end of the probe time, and a time-of-flight histogram is generated based on the final voltage of the capacitors of all analog counters;

[0020] The counting capacitors corresponding to the analog counters are configured with different numbers or different amounts of charge to filter the time-of-flight histogram.

[0021] The peak detection unit is configured to perform peak detection on the filtered flight histogram and extract flight time information.

[0022] The beneficial effects of this invention are:

[0023] This invention provides a method and system for extracting time-of-flight information. It utilizes an analog counting method based on the analog domain for histogram statistics. An analog counter acts as a counting and access device, corresponding to the histogram bin of the time-of-flight histogram. The time-of-flight histogram is generated through multiple detections by a single-photon avalanche diode. Based on the generated analog domain time-of-flight histogram, a simple comb filter and a complex FIR filter are implemented using a charge-sharing method without requiring an analog-to-digital converter to quantize the analog count values ​​in the histogram bin. Finally, effective time-of-flight information is extracted through peak detection. It is understood that a counting capacitor is correspondingly set for each analog counter. The number of counting capacitors set for the analog counters may be the same or different, or the charge of the multiple counting capacitors set for the analog counters may be different. The generated time-of-flight histogram is filtered, and then the peak value of the filtered time-of-flight histogram is detected to extract the time-of-flight information. In this way, by using multiple analog counters to generate analog domain time-of-flight histograms, the area of ​​the circuit module is greatly reduced. Moreover, the filtering operation can be achieved without using an analog-to-digital converter to quantize the count value of the analog counters, which can improve the signal-to-noise ratio and detect the peak value of the time-of-flight histogram to complete the extraction of effective time-of-flight information, thus significantly reducing the circuit resource consumption.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 This is a flowchart of a flight time information extraction method provided in an embodiment of the present invention;

[0026] Figure 2This is a schematic diagram of a histogram generation circuit provided in an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of generating a flight time histogram provided in an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram of a filtering process provided in an embodiment of the present invention;

[0029] Figure 5 This is another schematic diagram of the filtering process provided in an embodiment of the present invention;

[0030] Figure 6 This is another schematic diagram of the filtering process provided in an embodiment of the present invention;

[0031] Figure 7 This is another schematic diagram of the filtering process provided in an embodiment of the present invention;

[0032] Figure 8 This is a schematic diagram of a peak detection circuit provided in an embodiment of the present invention;

[0033] Figure 9 This is a circuit schematic diagram and its internal signal timing diagram of the comparator in the peak detection circuit provided in the embodiment of the present invention;

[0034] Figure 10 This is a schematic diagram of a flight time information extraction system provided in an embodiment of the present invention. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0036] Please see Figure 1 and Figure 2 , Figure 1 This is a flowchart of a flight time information extraction method provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of a histogram generation circuit provided in an embodiment of the present invention. The present invention provides a method for extracting time-of-flight information, comprising:

[0037] S101. Reset the count values ​​of multiple analog counters to the initial count values. Each analog counter is equipped with at least one counting capacitor. The counting capacitor is used to obtain the count value. Different analog counters correspond to different histogram bins in the flight time histogram.

[0038] S102, the histogram generation circuit receives multiple time-of-flight codewords from the time-to-digital converter; wherein the time-to-digital converter has an input coupled to a single-photon avalanche diode;

[0039] S103. During the detection time, select the analog counter corresponding to the digital address for the multiple received time-of-flight codewords, and increment the count value of the selected analog counter by a minimum counting step; wherein, at the end of the detection time, each analog counter obtains its final count value, and a time-of-flight histogram is generated based on the final count values ​​of all analog counters.

[0040] S104. Filter the flight time histogram according to the different number of counting capacitors or the different charge amounts of the counting capacitors set for different analog counters.

[0041] S105. Perform peak detection on the filtered time-of-flight histogram and extract the time-of-flight information.

[0042] For details, please continue to see Figure 1 and Figure 2 This embodiment provides a method for extracting time-of-flight information. A time-to-digital converter is used to obtain the flight time for each detection and outputs the flight time codeword; for example... Figure 2 As shown, bin1, bin2, ..., bin(n) represent histogram bins (bin) for different flight time information. The digital address of the histogram bin is proportional to the flight time codeword output by the time-to-digital converter. The addressing logic unit performs an addressing operation based on the flight time codeword output by the time-to-digital converter to find a histogram bin with the corresponding digital address. Analog counters 1, 2, ..., n are used as storage devices for the corresponding histogram bins. C1, C2, ..., Cn are the counting capacitors of analog counters 1, 2, ..., n, respectively. V1, V2, ..., Vn are the counting values ​​of the corresponding counting capacitors, which are also the counting values ​​of the corresponding histogram bins. Optionally, the analog counters adopt a charge transfer amplifier (CTA) structure, which can realize the successive increment counting function.

[0043] Please see Figure 3 , Figure 3 This is a schematic diagram of generating a time-of-flight histogram provided in an embodiment of the present invention. When a single-photon avalanche diode performs detection, a time-to-digital converter acquires the detected time-of-flight information. The addressing logic unit selects the histogram bin corresponding to the digital address based on the time-of-flight codeword output by the time-to-digital converter, so that the histogram bin count value increases by a minimum counting step. When the single-photon avalanche diode performs multiple detections, the histogram generation circuit performs histogram statistics on the results of each detection, and uses the analog counting function of the analog counter to generate the time-of-flight histogram of the analog domain in the pixel.

[0044] In this embodiment, histogram statistics are performed using an analog domain-based analog counting method. An analog counter acts as a counting and access device, corresponding to the histogram bin of the time-of-flight histogram. The time-of-flight histogram is generated through multiple probes by a single-photon avalanche diode. Based on the generated analog domain time-of-flight histogram, a simple comb filter and a complex FIR filter are implemented using a charge-sharing method without requiring an analog-to-digital converter to quantize the analog count values ​​in the histogram bin. Finally, effective time-of-flight information is extracted through peak detection. It is understood that a counting capacitor is correspondingly set for each analog counter, and each analog counter is equipped with a corresponding capacitor. The number of counting capacitors may be the same or different, or the charge amounts of the multiple counting capacitors corresponding to the analog counters may be different. The generated time-of-flight histogram is filtered, and then peak detection is performed on the filtered time-of-flight histogram to extract the time-of-flight information. In this way, by using multiple analog counters to generate the analog time-of-flight histogram, the area of ​​the circuit module is greatly reduced. Moreover, the filtering operation can be achieved without using an analog-to-digital converter to quantize the count values ​​of the analog counters, which can improve the signal-to-noise ratio and detect the peak value of the time-of-flight histogram to complete the extraction of effective time-of-flight information, thus significantly reducing the circuit resource consumption.

[0045] In an optional embodiment of the present invention, the expression for filtering the time-of-flight histogram is:

[0046]

[0047] Among them, h RAW h(m) is the input signal, h(m) is the filtered signal, N is the number of filter taps, N-1 is the filter order, and K FIR (m) represents the filter coefficients, and i is a variable whose value ranges from 0 to N-1.

[0048] Specifically, in this embodiment, the closer the distribution of the filtering coefficients is to the shape of the laser envelope during the filtering process, the better the filtering effect.

[0049] In an optional embodiment of the present invention, please refer to Figure 4 , Figure 4 This is a schematic diagram of a filtering process provided in an embodiment of the present invention. Filtering is performed on the m-th histogram box. Each analog counter is equipped with a corresponding counting capacitor, and the capacitance value of the counting capacitors corresponding to each analog counter is the same. When filtering the count values ​​of each analog counter in the time-of-flight histogram, the filtering coefficients are the same.

[0050] Specifically, in this embodiment, for cases with low signal-to-noise ratio, a filtering mechanism is added to the time-of-flight histogram based on the analog domain. The charge-sharing method is used to filter the time-of-flight histogram in the analog domain, which can realize a simple comb filter.

[0051] In this embodiment, please continue to refer to Figure 4 When the filter coefficient K FIR When all (m) are equal, the filter is also called a comb filter. A simple comb filter can be implemented using charge sharing. For example... Figure 4 As shown, the comb filter has 4 taps N and a filter order of 3. C(m-3), C(m-2), C(m-1), and C(m) are the counting capacitors of the analog counters in the histogram bins bin(m-3), bin(m-2), bin(m-1), and bin(m), respectively. V(m-3), V(m-2), V(m-1), and V(m) are the corresponding count values. Switch k is kept open before the filtering operation and is turned on during the filtering operation. According to the principle of charge conservation, the charge in different counting capacitors is shared through the turned-on switch, ultimately achieving the same amount of charge stored in each counting capacitor, thus realizing average filtering. Here, h(m) is the signal after filtering, and the expression for average filtering is:

[0052]

[0053] The capacitance values ​​set for the counting capacitors in the analog counters are all the same, so the filter coefficients in formula (2) are all 1 / 4. For the lidar currently used for long-distance detection, its pulse width is usually tens of nanoseconds, and the laser envelope is approximately a square wave. The distribution of the filter coefficients of this comb filter is close to the shape of the laser envelope, which is a simple and effective filtering strategy.

[0054] It should be noted that in this embodiment, filtering is described only for the m-th histogram bin, including the process of adjusting the filter weights described below. The entire filtering process requires multiple stacking operations.

[0055]

[0056] The above formula requires the count values ​​of four counting capacitors, V(m-3), V(m-2), V(m-1), and V(m), to be used when filtering the m-th histogram bin. However, when filtering the (m+1)-th histogram bin, the count values ​​of the same four capacitors are required, and so on. Throughout the entire filtering process, the analog counter needs to be set with corresponding counting capacitors for each processing step. For example, when the filter tap number N is set to 4, the count value of the m-th analog counter needs to be read when filtering the (m+3), (m+2), (m+1), and (m)-th histogram bins. Therefore, four counting capacitors need to be set initially. If weight adjustments are needed later, more capacitors are added; the different charges of these added capacitors represent increases or decreases in weight.

[0057] In an optional embodiment of the present invention, please refer to Figure 5 , Figure 5 This is another schematic diagram of the filtering process provided in the embodiment of the present invention. Filtering is performed on the m-th histogram box. At least one of the multiple analog counters is equipped with multiple counting capacitors. The multiple counting capacitors equipped with the analog counter have the same capacitance value and the same charge. Filtering is performed on the time-of-flight histogram, and the filtering coefficient corresponding to the count value of the analog counter increases.

[0058] For details, please continue to see Figure 5 In this embodiment, filtering is performed by setting multiple counting capacitors corresponding to an analog counter; for example... Figure 5 As shown, the m-th analog counter is equipped with three counting capacitors, namely C(m) and two C`(m). The three counting capacitors have the same capacitance value and carry the same amount of charge, that is, their initial voltage V`(m) = V(m). By sharing the charge, the filter coefficient corresponding to the count value of the m-th analog counter is increased.

[0059] In an optional embodiment of the present invention, please refer to Figure 6 , Figure 6 This is another schematic diagram of the filtering process provided in the embodiment of the present invention. Filtering is performed on the m-th histogram box. At least one of the multiple analog counters is equipped with multiple counting capacitors. The multiple counting capacitors equipped with the analog counter have the same capacitance value, and at least some of the counting capacitors have zero charge. Filtering is performed on the time-of-flight histogram, and the filtering coefficient corresponding to the count value of the analog counter is reduced.

[0060] For details, please continue to see Figure 6In this embodiment, filtering is performed by setting multiple counting capacitors corresponding to an analog counter; for example... Figure 6 As shown, the m-th analog counter is equipped with three counting capacitors, namely C(m) and two C'(m). The three counting capacitors have the same capacitance value. The two C'(m) carry zero charge, that is, their initial voltage V'(m) = 0. By sharing the charge, the filter coefficient corresponding to the count value of the m-th analog counter is reduced.

[0061] In an optional embodiment of the present invention, please refer to Figure 7 , Figure 7 This is another schematic diagram of the filtering process provided in the embodiment of the present invention. At least one of the multiple analog counters is provided with two counting capacitors. The two counting capacitors provided with the analog counter have the same capacitance value. The charge of one of the counting capacitors is set to zero after each charge sharing. The time-of-flight histogram is filtered. Through multiple charge sharing, the filtering coefficient corresponding to the count value of the analog counter is reduced.

[0062] For details, please continue to see Figure 7 In this embodiment, filtering is performed by setting multiple counting capacitors corresponding to an analog counter; for example... Figure 7 As shown, the m-th analog counter is equipped with two counting capacitors, namely C(m) and C`(m), with the same capacitance value. The charge carried by C`(m) is zero, that is, its initial voltage V`(m) = 0. After one charge sharing, the switch k` is turned on, so that C`(m) releases the charge to ground, that is, V`(m) is reset to 0 to prepare for the next charge sharing. Through multiple charge sharing, the filter coefficient corresponding to the count value of the m-th analog counter is reduced. Because reducing the number of additional counting capacitors can save area.

[0063] In an optional embodiment of the present invention, please refer to Figure 8 , Figure 8 This is a schematic diagram of a peak detection circuit provided in an embodiment of the present invention, which performs peak detection on the filtered time-of-flight histogram and extracts time-of-flight information, including:

[0064] A reference ramp voltage signal is generated by a ramp voltage generator, and the reference ramp voltage signal is input to the negative input terminals of multiple comparators respectively.

[0065] The count values ​​of each analog counter in the filtered flight histogram are input to the positive input terminals of multiple comparators;

[0066] When the difference between the count value of each analog counter and the reference ramp voltage signal is greater than a fixed threshold, the comparator outputs a positive step signal.

[0067] Based on the signals output by multiple comparators, the peak value of the time-of-flight histogram is detected, and the time-of-flight information is extracted.

[0068] For details, please continue to see Figure 8 In this embodiment, after appropriate filtering, the peak value of the time-of-flight histogram is highlighted, the half-width is narrowed, and the signal-to-noise ratio is improved, before peak detection is performed. (Reference) Figure 8 A reference ramp voltage signal, `ramp`, is generated by a ramp voltage generator and connected to the negative input of a comparator. The filtered time-of-flight histogram box count (stored in a counting capacitor) is connected to the positive input of the comparator. Optionally, the comparators are COMP1, COMP2, COMP3, ..., COMP(m). When the difference between the count value and the reference ramp voltage signal `ramp` is greater than a fixed threshold `Vth` (`Vth>0`), the comparator outputs a positive step signal, i.e., a rising edge signal. During the ramp voltage generation process, a rising edge arrival sequence detection circuit monitors the comparator outputs, i.e., monitors `out1`, `out2`, `out3`, ..., `out(m)`. The comparator whose rising edge signal is detected first indicates that the time-of-flight histogram box count value input to that comparator is the largest in this comparison. By comparing multiple histogram box count values, the peak value of the time-of-flight histogram can be detected, which is the valid time-of-flight information.

[0069] Please see Figure 9 , Figure 9 This is a circuit schematic diagram and internal signal timing diagram of the comparator in the peak detection circuit provided in this embodiment of the invention. The comparator adopts a space-saving dual-transistor comparator scheme. The RST terminal controls the reset of the comparator for initialization, and the comparator outputs a low-level signal. When the difference between the time-of-flight histogram box count value V(m) and the ramp voltage ramp is greater than the threshold Vth, transistor M1 is turned on, and the comparator outputs a positive step signal.

[0070] Through the above process, without using an analog-to-digital converter to quantize the final count value of the histogram bin in the time-of-flight histogram bin, filtering is performed to improve the signal-to-noise ratio, and the peak value of the histogram is detected to complete the extraction of the effective flight time.

[0071] Based on the same inventive concept, please refer to Figure 10 , Figure 10 This is a schematic diagram of a flight time information extraction system provided in an embodiment of the present invention, and in conjunction with... Figure 2 As shown, the present invention also provides a flight time information extraction system, comprising:

[0072] Multiple single-photon avalanche diodes are configured to generate SPAD events;

[0073] Multiple time-to-digital converters are coupled to multiple single-photon avalanche diodes; wherein each time-to-digital converter is configured to generate multiple time-of-flight codewords based on SPAD events generated by the single-photon avalanche diodes;

[0074] A histogram generation circuit, coupled to multiple time-to-digital converters; wherein the histogram generation circuit includes:

[0075] The addressing logic unit includes multiple outputs and inputs configured to receive multiple time-of-flight codewords from the time-to-digital converter; and,

[0076] Multiple analog counters, including inputs coupled to multiple outputs of the addressing logic unit; each analog counter is provided with at least one counting capacitor;

[0077] The addressing logic unit is configured to select an analog counter corresponding to a digital address based on multiple received time-of-flight codewords during the probe time, and to activate the input of the selected analog counter; wherein the selected analog counter is configured to increment its count value by a minimum counting step when the input of the selected analog counter is activated; wherein the counting capacitor of each analog counter is configured to have a final voltage at the end of the probe time, and a time-of-flight histogram is generated based on the final voltage of the capacitors of all the analog counters;

[0078] The counting capacitors corresponding to the analog counters are configured with different numbers or amounts of charge to filter the time-of-flight histogram.

[0079] The peak detection unit is configured to perform peak detection on the filtered flight histogram and extract flight time information.

[0080] In an optional embodiment of the present invention, please continue to refer to Figure 4 Each analog counter is equipped with a corresponding counting capacitor; wherein, the first terminal of the counting capacitor corresponding to the analog counter is electrically connected to the ground terminal, and the second terminal of the counting capacitor is electrically connected to the second terminal of the counting capacitor corresponding to the adjacent analog counter through a switch.

[0081] For details, please continue to see Figure 4 Each analog counter has a corresponding counting capacitor. The first terminal of the counting capacitor is electrically connected to ground, and the second terminal of the counting capacitor is electrically connected to the second terminal of the corresponding counting capacitor of the adjacent analog counter through a switch. Alternatively, it can be understood that the first terminal of all counting capacitors is electrically connected to ground, and the second terminal of all counting capacitors is electrically connected to the second terminal of the adjacent counting capacitor through switch k. Figure 4As shown, the second terminal of the counting capacitor C(m-3) is electrically connected to the second terminal of the counting capacitor C(m-2) through switch k, and the second terminal of the counting capacitor C(m-2) is electrically connected to the second terminals of the counting capacitor C(m-3) and the second terminal of the counting capacitor C(m-1) through switch k. Thus, for the case of low signal-to-noise ratio, a filtering mechanism is added to the time-of-flight histogram based on the analog domain, and a charge-sharing method is used to filter the time-of-flight histogram in the analog domain, which can realize a simple comb filter.

[0082] In an optional embodiment of the present invention, please continue to refer to Figure 5 At least one of the multiple analog counters is equipped with multiple counting capacitors; wherein, the first terminal of the counting capacitors corresponding to the analog counters and the multiple counting capacitors are electrically connected to the ground terminal, and the second terminal of the counting capacitors is electrically connected to the second terminal of the counting capacitors corresponding to the adjacent analog counters through a switch.

[0083] For details, please continue to see Figure 5 In this embodiment, at least one analog counter is provided with multiple counting capacitors. The first end of each counting capacitor is electrically connected to ground, and the second end of each counting capacitor is electrically connected to the second end of the corresponding counting capacitor of the adjacent analog counter via a switch. Alternatively, the first end of each counting capacitor is electrically connected to ground, and the second end of each counting capacitor is electrically connected to the second end of the adjacent counting capacitor via a switch. Figure 5 As shown, the second terminal of the counting capacitor C(m-3) is electrically connected to the second terminal of the counting capacitor C(m-2) through switch k. The second terminal of the counting capacitor C(m-2) is electrically connected to the second terminals of the counting capacitors C(m-3) and C(m-1) through switch k. Filtering is performed for the m-th histogram bin. Figure 5 The counting capacitor C(m) has the same capacitance value as the two C`(m) and carries the same amount of charge, that is, its initial voltage V`(m) = V(m). Through charge sharing, the filter coefficient corresponding to the count value of the m-th analog counter is increased.

[0084] In an optional embodiment of the present invention, please continue to refer to Figures 6-7 At least one of the multiple analog counters is provided with multiple counting capacitors; wherein, the first terminal of the counting capacitor provided for the analog counter is electrically connected to the ground terminal, the second terminal of the counting capacitor is electrically connected to the second terminal of the counting capacitor provided for the adjacent analog counter through a switch, and the second terminal of at least one of the multiple counting capacitors provided for the analog counter is electrically connected to the ground terminal through a switch.

[0085] For details, please continue to see Figures 6-7In this embodiment, at least one analog counter is provided with multiple counting capacitors. The first end of each counting capacitor is electrically connected to ground, and the second end of each counting capacitor is electrically connected to the second end of the corresponding counting capacitor of the adjacent analog counter via a switch. Alternatively, it can be understood that the first end of each counting capacitor is electrically connected to ground, and the second end of each counting capacitor is electrically connected to the second end of the corresponding counting capacitor via a switch. At least one of the multiple counting capacitors provided for the analog counter has its second end connected to ground via a switch. Figures 6-7 As shown, the second terminal of counting capacitor C(m-3) is electrically connected to the second terminal of counting capacitor C(m-2) through switch k. The second terminal of counting capacitor C(m-2) is electrically connected to the second terminals of counting capacitor C(m-3) and counting capacitor C(m-1) through switch k. The second terminal of counting capacitor C`(m) is grounded through switch k`. Filtering is performed for the m-th histogram bin, as follows: Figure 6 As shown, the m-th analog counter is equipped with three counting capacitors, namely C(m) and two C'(m). All three capacitors have the same capacitance value. The two C'(m) carry zero charge, meaning their initial voltage V'(m) = 0. This charge sharing reduces the filtering coefficient corresponding to the count value of the m-th analog counter. Filtering is then performed on the m-th histogram box, as follows: Figure 7 As shown, the m-th analog counter is equipped with two counting capacitors, namely C(m) and C`(m), with the same capacitance value. The charge carried by C`(m) is zero, that is, its initial voltage V`(m) = 0. After one charge sharing, the switch k` is turned on, so that C`(m) releases the charge to ground, that is, V`(m) is reset to 0 to prepare for the next charge sharing. Through multiple charge sharing, the filter coefficient corresponding to the count value of the m-th analog counter is reduced. Because reducing the number of additional counting capacitors can save area.

[0086] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or device comprising a list of elements includes not only those elements but also other elements not expressly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device comprising said element. Terms such as "connected" or "linked" are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect. The orientations or positional relationships indicated by terms such as "upper," "lower," "left," and "right" are based on the orientations or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0087] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0088] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for extracting flight time information, characterized in that, include: The count values ​​of multiple analog counters are reset to their initial count values. Each analog counter is equipped with at least one counting capacitor, which is used to acquire the count value. Different analog counters correspond to different histogram bins in the time-of-flight histogram. The histogram generation circuit receives multiple time-of-flight codewords from a time-to-digital converter; wherein the time-to-digital converter has an input coupled to a single-photon avalanche diode; During the detection time, an analog counter corresponding to the digital address is selected for each of the received multiple time-of-flight codewords, and the count value of the selected analog counter is increased by a minimum counting step; wherein, at the end of the detection time, each analog counter obtains a final count value, and a time-of-flight histogram is generated based on the final count values ​​of all the analog counters; The time-of-flight histogram is filtered based on the different numbers of counting capacitors or the different charges of the counting capacitors corresponding to the different analog counters; the expression for filtering the time-of-flight histogram is: ； in, For input signal, The signal after filtering. This represents the number of filter taps. Let the filter order be . These are the filter coefficients. As variables, The value range is 0~ ; Peak detection is performed on the filtered time-of-flight histogram to extract time-of-flight information; including: A reference ramp voltage signal is generated by a ramp voltage generator, and the reference ramp voltage signal is input to the negative input terminals of multiple comparators respectively. The count values ​​of each analog counter in the filtered flight histogram are input to the positive input terminals of multiple comparators; When the difference between the count value of each analog counter and the reference ramp voltage signal is greater than a fixed threshold, the comparator outputs a positive step signal. Based on the signals output by the multiple comparators, the peak value of the time-of-flight histogram is detected, and the time-of-flight information is extracted.

2. The method for extracting flight time information according to claim 1, characterized in that, Regarding the first Each histogram box is used for filtering. Each analog counter is equipped with a corresponding counting capacitor, and the capacitance value of the counting capacitors corresponding to each analog counter is the same. When filtering the count values ​​of each analog counter in the time-of-flight histogram, the filtering coefficients are the same.

3. The method for extracting flight time information according to claim 1, characterized in that, Regarding the first The histogram is filtered by a plurality of histogram boxes, and at least one of the plurality of analog counters is provided with a plurality of counting capacitors; and the capacitance values ​​and charge amounts of the plurality of counting capacitors provided with the analog counters are the same; the time-of-flight histogram is filtered, and the filtering coefficient corresponding to the count value of the analog counter is increased.

4. The method for extracting flight time information according to claim 1, characterized in that, Regarding the first The histogram is filtered by a plurality of histogram boxes, and at least one of the plurality of analog counters is provided with a plurality of counting capacitors; and the capacitance values ​​of the plurality of counting capacitors provided with the analog counters are the same, and at least some of the counting capacitors have zero charge; the time-of-flight histogram is filtered, and the filtering coefficient corresponding to the count value of the analog counter is reduced.

5. The method for extracting flight time information according to claim 1, characterized in that, At least one of the plurality of analog counters is provided with two counting capacitors; and the two counting capacitors provided with the analog counter have the same capacitance value, and the charge of one of the counting capacitors is set to zero after each charge sharing; the time-of-flight histogram is filtered, and through multiple charge sharing, the filtering coefficient corresponding to the count value of the analog counter is reduced.

6. A flight time information extraction system, characterized in that, include: Multiple single-photon avalanche diodes are configured to generate SPAD events; Multiple time-to-digital converters are coupled to the multiple single-photon avalanche diodes; wherein each time-to-digital converter is configured to generate multiple time-of-flight codewords based on SPAD events generated by the single-photon avalanche diodes; A histogram generation circuit, coupled to multiple time-to-digital converters; wherein the histogram generation circuit includes: The addressing logic unit includes multiple outputs and inputs configured to receive multiple time-of-flight codewords from the time-to-digital converter; and, Multiple analog counters, including inputs coupled to the multiple outputs of the addressing logic unit; each analog counter is provided with at least one counting capacitor; The addressing logic unit is configured to select an analog counter corresponding to a digital address based on multiple received time-of-flight codewords during the probe time, and to activate the input of the selected analog counter; wherein the selected analog counter is configured to increment its count value by a minimum counting step when the input of the selected analog counter is activated; wherein the counting capacitor of each analog counter is configured to have a final voltage at the end of the probe time, and a time-of-flight histogram is generated based on the final voltage of the capacitors of all the analog counters; The counting capacitors corresponding to the analog counters are configured with different numbers or different charges to filter the time-of-flight histogram; the expression for filtering the time-of-flight histogram is: ； in, For input signal, The signal after filtering. This represents the number of filter taps. Let the filter order be . These are the filter coefficients. As variables, The value range is 0~ ; The peak detection unit is configured to perform peak detection on the filtered flight histogram and extract flight time information; including: A reference ramp voltage signal is generated by a ramp voltage generator, and the reference ramp voltage signal is input to the negative input terminals of multiple comparators respectively. The count values ​​of each analog counter in the filtered flight histogram are input to the positive input terminals of multiple comparators; When the difference between the count value of each analog counter and the reference ramp voltage signal is greater than a fixed threshold, the comparator outputs a positive step signal. Based on the signals output by the multiple comparators, the peak value of the time-of-flight histogram is detected, and the time-of-flight information is extracted.

7. The flight time information extraction system according to claim 6, characterized in that, Each analog counter is provided with a corresponding counting capacitor; wherein, the first terminal of the counting capacitor provided for the analog counter is electrically connected to the ground terminal, and the second terminal of the counting capacitor is electrically connected to the second terminal of the counting capacitor provided for the adjacent analog counter through a switch.

8. The flight time information extraction system according to claim 6, characterized in that, At least one of the plurality of analog counters is provided with a plurality of counting capacitors; wherein, the first terminal of the counting capacitor provided with the analog counter and the plurality of counting capacitors are electrically connected to ground, and the second terminal of the counting capacitor is electrically connected to the second terminal of the counting capacitor provided with the adjacent analog counter via a switch; or, the first terminal of the counting capacitor provided with the analog counter is electrically connected to ground, the second terminal of the counting capacitor is electrically connected to the second terminal of the counting capacitor provided with the adjacent analog counter via a switch, and the second terminal of at least one of the plurality of counting capacitors provided with the analog counter is electrically connected to ground via a switch.

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