A SPAD coarse-fine histogram synchronous quantization system based on pulse time interval weighting

Abstract

This invention discloses a SPAD coarse and fine histogram synchronous quantization system based on pulse time interval weighting. The system receives photon trigger events from a single-photon avalanche diode (SPAD) via a pulse preprocessing module, preprocesses these events, and outputs a weighted time interval. A fine photon event measurement module performs fine histogram statistics, filtering reconstruction, and peak calculation on the weighted time interval, outputting a denoised fine histogram and an overflow flag. A coarse photon event measurement module performs distribution statistics based on the weighted time interval and a second time interval between the measured photon trigger time and the laser emission time, outputting a coarse histogram. A time-of-flight calculation module calculates the time of flight based on the denoised fine histogram, the overflow flag, and the coarse histogram, outputting the target time of flight. This invention reduces histogram storage resource consumption through synchronous quantization of coarse and fine histograms, while simultaneously improving the measurement frame rate compared to step-by-step histogram calculations.

Description

Technical Field

[0001] This invention belongs to the field of single-photon detection and integrated circuit technology, and particularly relates to a SPAD coarse and fine histogram synchronization quantization system based on pulse time interval weighting. Background Technology

[0002] Due to their extremely high detection sensitivity and picosecond-level time resolution, single-photon avalanche diodes (SPADs) are widely used in photoelectric detection systems such as time-of-flight measurement. SPAD-based lidar systems can achieve long-distance, high-precision three-dimensional measurements under relatively low transmission power conditions and are gradually being applied in fields such as robotic vacuum cleaners, autonomous driving, and automata.

[0003] However, limited by the high-gain and nonlinear response characteristics of SPAD devices, the number of effective events triggered by target echo photons is relatively small during a single detection process. Measurement results are easily affected by dark counting and ambient background noise, resulting in a low overall signal-to-noise ratio (SNR). To improve the SNR, existing technologies typically employ histogram-based statistical methods to accumulate multiple measurement results, thereby enhancing the statistical significance of the target echo signal. However, histogram statistical methods usually require a corresponding storage unit for each time-resolution unit to record the number of photon triggers within different time periods, resulting in significant storage resource consumption. As the measurement distance and time resolution increase, the number of time-resolution units required for the histogram increases significantly, leading to a doubling of storage resource demands, thus restricting the improvement of system integration and the expansion of imaging resolution.

[0004] To address the aforementioned issues, existing technologies have proposed a step-by-step histogram statistical method, dividing the measurement process into coarse and fine measurement stages and reusing storage resources through time-division multiplexing, thus reducing the number of histogram storage units required to some extent. However, this type of method typically requires multiple measurement cycles to complete one effective imaging, resulting in a low system imaging frame rate, which is insufficient to meet the needs of high frame rate imaging applications. Furthermore, traditional histogram statistical methods usually employ a linear accumulation approach to statistically analyze photon-triggered events. During histogram construction, events triggered by target echo photons and those triggered by background photons are given the same weight, failing to effectively distinguish the impact of different types of photon events on the measurement results. In application scenarios with strong background light or low signal-to-noise ratio, this accumulation method easily weakens the statistical advantage of effective echo photons, thereby limiting further improvements in the measurement signal-to-noise ratio.

[0005] In summary, while existing SPAD-based lidar systems have improved the measurement signal-to-noise ratio, they still face problems such as high consumption of histogram storage resources, limited imaging frame rate, and insufficient utilization efficiency of effective echo trigger events, which restrict the further development of the system in high-resolution, high-frame-rate application scenarios. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a SPAD coarse and fine histogram synchronous quantization system based on pulse time interval weighting.

[0007] The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides a SPAD coarse-fine histogram synchronization quantization system based on pulse time interval weighting, comprising: The pulse preprocessing module is used to receive photon triggering events output by the single-photon avalanche diode SPAD, preprocess the photon triggering events, and output a weighted time interval. The photon event fine measurement module is used to perform fine histogram statistics, filtering reconstruction and peak calculation on the weighted time interval, and output a denoised fine histogram and an overflow flag. The photon event coarse measurement module is used to perform distribution statistics based on the weighted time interval and the second time interval between the photon triggering time and the laser emission time of the measured photon triggering event, and output a coarse histogram. The time-of-flight calculation module is used to calculate the time of flight based on the denoised fine histogram, overflow flag, and coarse histogram, and output the target time of flight.

[0008] This invention provides a SPAD coarse and fine histogram synchronous quantization system based on pulse time interval weighting. By detecting the correlation of photon triggering events, different weights are assigned to the events generated by echo photons, thereby increasing the equivalent triggering probability of echo photons. The synchronous quantization of coarse and fine histograms reduces the consumption of histogram storage resources, while improving the measurement frame rate compared to step-by-step histograms.

[0009] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of a SPAD coarse and fine histogram synchronization quantization system based on pulse time interval weighting provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the processing procedure of a SPAD coarse and fine histogram synchronous quantization system based on pulse time interval weighting according to an embodiment of the present invention; Figure 3This is a schematic diagram of the structure of the photon event fine measurement module 120 and the coarse histogram statistical circuit 1302 in an embodiment of the present invention. Detailed Implementation

[0011] 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.

[0012] This invention provides a SPAD coarse-fine histogram synchronization quantization system based on pulse time interval weighting. See also... Figure 1 and Figure 2 The system includes: The pulse preprocessing module 110 is used to receive the photon triggering events output by the single-photon avalanche diode SPAD, preprocess the photon triggering events, and output a weighted time interval.

[0013] For example, a single-photon avalanche diode (SPAD) receives ambient light reflected from the scene and outputs a photon trigger event. The pulse preprocessing module 110 measures the first time interval between the photon trigger moment of the photon trigger event and the rising edge of the system clock. Then, by comparing the time intervals between adjacent photon trigger moments within a single clock cycle, a comparison result is obtained. The first time interval is then weighted using the comparison result to obtain a weighted time interval. During the weighting process, the smaller the time interval, the greater the weight. The weighted data effectively increases the photon trigger probability.

[0014] The photon event fine measurement module 120 is used to perform fine histogram statistics, filtering reconstruction and peak calculation on the weighted time interval, and output a denoised fine histogram and an overflow flag.

[0015] For example, the photon event fine measurement module 120 statistically calculates the distribution characteristics of the weighted time interval to obtain a fine histogram with a single-peak distribution; then the fine histogram is copied and spliced, and then smoothed and filtered to obtain a denoised fine histogram, wherein the filtering window can be set to half the laser pulse width; finally, the peak position after filtering is found by peak calculation on the denoised fine histogram.

[0016] The photon event coarse measurement module 130 is used to perform distribution statistics based on the weighted time interval and the second time interval between the photon triggering time and the laser emission time of the measured photon triggering event, and output a coarse histogram.

[0017] For example, the photon event coarse measurement module 130 receives the weighted time interval, measures the second time interval between the laser emission time and the photon triggering time, and based on the weighted time interval, calculates the phase distribution between the photon triggering event and the laser emission time, and outputs a coarse histogram.

[0018] The flight time calculation module 140 is used to calculate the flight time based on the denoised fine histogram, overflow flag and coarse histogram, and output the target flight time.

[0019] For example, the time-of-flight calculation module 140 reads the measurement results (i.e., coarse histogram) from the photon event coarse measurement module 130 and the measurement results (i.e., denoised fine histogram and overflow flag) from the photon time fine measurement module 120 to reconstruct the time of flight. First, based on the overflow flag, the highest peak position or the second highest peak position of the coarse histogram is selected as the target coarse measurement result. Assuming the overflow flag is high and the trigger time of the highest peak (i.e., the highest peak position) is greater than the trigger time of the second highest peak position (i.e., the second highest peak position), then the highest peak position is selected as the target coarse measurement result. This effectively solves the extreme case where the laser is bisected by two coarse bins, obtaining the accurate position of the laser peak. Finally, based on the target coarse measurement result and the peak position of the denoised fine histogram, the target time of flight is calculated, and the precise distance of the object is measured.

[0020] This embodiment presents a SPAD coarse and fine histogram synchronous quantization system based on pulse time interval weighting. By detecting the correlation of photon triggering events, different weights are assigned to the events generated by echo photons, thereby increasing the equivalent triggering probability of echo photons. The synchronous quantization of coarse and fine histograms reduces the consumption of histogram storage resources. At the same time, it is faster than step-by-step histogram processing, and more measurements are performed per unit time, thereby improving the measurement frame rate.

[0021] In one alternative embodiment, the pulse preprocessing module 110 includes: The first time-to-digital converter circuit 1101 is used to measure the first time interval between the photon triggering moment of the photon triggering event and the rising edge of the system clock.

[0022] Comparison circuit 1102 is used to compare the time interval between two adjacent photon triggering moments within a single clock cycle and output the comparison result.

[0023] The weighting circuit 1103 weights the first time interval according to the comparison result and outputs the weighted time interval.

[0024] For example, the first time interval can be output as a series of 0-1 interval digital signals. The first time-to-digital conversion circuit 1101 uses methods such as synchronous sampling and time-to-digital conversion to record photon triggering events and convert the photon triggering events into timestamp information. The first time interval obtained by calculating and statistically analyzing the timestamp information can be in the form of a time-digital code, providing a data basis for the statistical operation of the subsequent histogram accumulation unit. The specific weighting process of the weighting circuit 1103 is as follows: for example, taking 4 photon triggering events as a group, if the time interval between two adjacent photon triggering times in each group is 1-8, then the time-digital code corresponding to the first time interval is incremented by 7; if the time interval between two adjacent photon triggering times is 9-16, then the time-digital code corresponding to the first time interval is incremented by 3; if the time interval between two adjacent photon triggering times is 17-24, then the time-digital code corresponding to the first time interval is incremented by 1. This embodiment can improve the equivalent triggering probability of echo photons, providing a data basis for subsequent histogram statistical operations.

[0025] In one alternative embodiment, refer to Figure 3 The photon event fine measurement module 120 includes: The fine histogram statistical circuit 1201 is used to statistically analyze the distribution characteristics of the weighted time interval between the photon triggering time and the rising edge of the system clock, and output a fine histogram.

[0026] Optionally, the fine histogram statistical circuit 1201 includes a first accumulation circuit 12011 and a first storage circuit 12012; the first accumulation circuit 12011 is used to accumulate the weighted time interval and the current stored data of the first storage circuit to output a fine histogram; the first storage circuit 12012 is used to store the fine histogram.

[0027] For example, the first storage circuit 12012 uses the first time interval as its index address. The current stored data of the first storage circuit is the fine histogram stored in the previous cycle.

[0028] The cyclic convolution filter circuit 1202 is used to perform convolution filtering on the fine histogram and output a denoised fine histogram.

[0029] Optionally, the cyclic convolution filter circuit 1202 includes a data splicing unit 12021, a convolution unit 12022, and a weight storage unit 12023; the data splicing unit 12021 is used to copy and splice the fine histogram and output the spliced ​​fine histogram; the convolution unit 12022 is used to convolve the spliced ​​fine histogram and the weight coefficients pre-stored in the weight storage unit and output the denoised fine histogram; the weight storage unit 12023 is used to store the weight coefficients.

[0030] For example, the cyclic convolution filter circuit 1202 performs convolution filtering on the fine histogram to suppress the noise components it contains, outputting a denoised fine histogram. In this embodiment, the cyclic convolution filter circuit 1202 reduces the phase shift phenomenon of the laser, increasing the equivalent signal-to-noise ratio. Here, the weighting coefficients can be flexibly set by those skilled in the art according to actual conditions.

[0031] The peak calculation circuit 1203 is used to perform peak calculation on the denoised fine histogram and output an overflow flag.

[0032] Optionally, the peak calculation circuit 1203 includes: a first peak detection circuit 12031, used to perform peak detection on the denoised fine histogram and output the peak position; and an overflow detection circuit 12032, used to compare the number of bins corresponding to the peak position with the number of bins in the fine histogram, and if the number of bins corresponding to the peak position is greater than the number of bins in the fine histogram, output an overflow flag.

[0033] For example, after outputting the overflow flag, the peak position of the denoised fine histogram is replaced with the difference between the number of bins corresponding to the peak position output by the peak detection circuit 12031 and the number of bins in the fine histogram, thus obtaining the updated peak position of the denoised fine histogram. In this embodiment, the peak calculation circuit 1203 performs peak calculation on the denoised fine histogram to restore the peak position of the fine histogram.

[0034] In one alternative embodiment, the photon event coarse measurement module 130 includes: The second time-to-digital conversion circuit 1301 is used to measure the second time interval between the photon triggering moment and the laser emission moment of the photon triggering event.

[0035] The coarse histogram statistical circuit 1302 is used to statistically analyze the distribution characteristics of the second time interval between the photon triggering time and the laser emission time based on the weighted time interval, and output a coarse histogram.

[0036] For example, the second time-to-digital converter circuit 1301 measures the second time interval, which may be in the form of a time-digital code. (Refer to...) Figure 3 The coarse histogram statistical circuit 1302 includes a counting circuit 13021, a second accumulation circuit 13022, and a second storage circuit 13023. The counting circuit 13021 is used to count the second time interval between the laser emission time and the photon triggering time based on a weighted time interval. The second accumulation circuit 13022 is used to accumulate the output of the counting circuit 13021 and the currently stored data of the second storage circuit to output a coarse histogram. The second storage circuit 13023 is used to store the coarse histogram.

[0037] In one alternative embodiment, the time-of-flight calculation module 140 includes: The second peak detection circuit 1401 is used to detect the peak position of the coarse histogram and output the highest peak position and the second highest peak position.

[0038] The interval selection circuit 1402 is used to select the highest peak position or the second highest peak position as the target coarse measurement result based on the overflow flag; and to determine the target flight time based on the target coarse measurement result and the updated peak position of the denoised fine histogram.

[0039] For example, the highest or second-highest peak position is selected as the target coarse measurement result based on the overflow flag. Specifically: if the overflow flag is high and the trigger time of the highest peak is less than the trigger time of the second-highest peak, then the second-highest peak position is selected as the target coarse measurement result. If the overflow flag is high and the trigger time of the highest peak is greater than the trigger time of the second-highest peak, then the highest peak position is selected as the target coarse measurement result. If the overflow flag is low and the trigger time of the highest peak is less than the trigger time of the second-highest peak, then the highest peak position is selected as the target coarse measurement result. If the overflow flag is low and the trigger time of the highest peak is greater than the trigger time of the second-highest peak, then the second-highest peak position is selected as the target coarse measurement result.

[0040] The target flight time is determined based on the coarse measurement results and the peak position of the denoised fine histogram. The specific process is as follows: multiply the difference between the coarse measurement result and 32 to obtain the product. Add the product to the peak position of the denoised fine histogram to obtain the fine bin value between the photon triggering time and the laser emission time. Multiply the fine bin value by 0.125 to obtain the target flight time in nanoseconds.

[0041] This invention provides a SPAD coarse and fine histogram synchronous quantization system based on pulse time interval weighting. By detecting the correlation of photon triggering events, different weights are assigned to the events generated by echo photons, thereby increasing the equivalent triggering probability of echo photons. The synchronous quantization of coarse and fine histograms reduces the consumption of histogram storage resources, while improving the measurement frame rate compared to step-by-step histograms.

[0042] It should be noted that the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention.

[0043] 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. Moreover, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0044] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings and the disclosure in carrying out the claimed invention. In the description of the invention, the word "comprising" does not exclude other components or steps, "a" or "an" does not exclude a plurality, and "a plurality" means two or more, unless otherwise explicitly specified. Furthermore, while different embodiments may describe certain measures, this does not mean that these measures cannot be combined to produce good results.

[0045] 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 SPAD coarse-fine histogram synchronization quantization system based on pulse time interval weighting, characterized in that, include: The pulse preprocessing module is used to receive photon triggering events output by a single-photon avalanche diode (SPAD), preprocess the photon triggering events, and output a weighted time interval. The photon event fine measurement module is used to perform fine histogram statistics, filtering reconstruction and peak calculation on the weighted time interval, and output a denoised fine histogram and an overflow flag. The photon event coarse measurement module is used to perform distribution statistics based on the weighted time interval and the second time interval between the photon triggering time and the laser emission time of the measured photon triggering event, and output a coarse histogram. The flight time calculation module is used to calculate the flight time based on the denoised fine histogram, the overflow flag, and the coarse histogram, and output the target flight time.

2. The SPAD coarse-fine histogram synchronization quantization system based on pulse time interval weighting according to claim 1, characterized in that, The pulse preprocessing module includes: The first time-to-digital conversion circuit is used to measure the first time interval between the photon triggering moment of the photon triggering event and the rising edge of the system clock. The comparator circuit is used to compare the time interval between two adjacent photon triggering moments within a single clock cycle and output the comparison result. The weighting circuit weights the first time interval based on the comparison result and outputs a weighted time interval.

3. The SPAD coarse-fine histogram synchronization quantization system based on pulse time interval weighting according to claim 2, characterized in that, The photon event fine measurement module includes: A fine histogram statistical circuit is used to statistically analyze the distribution characteristics of the weighted time interval between the photon triggering time and the rising edge of the system clock, and output a fine histogram. A cyclic convolution filter circuit is used to perform convolution filtering on the fine histogram and output a denoised fine histogram. The peak calculation circuit is used to perform peak calculation on the denoised fine histogram and output an overflow flag.

4. The SPAD coarse-fine histogram synchronization quantization system based on pulse time interval weighting according to claim 3, characterized in that, The fine histogram statistical circuit includes a first accumulation circuit and a first storage circuit; The first accumulation circuit is used to accumulate the weighted time interval and the current stored data of the first storage circuit, and output the fine histogram; The first storage circuit is used to store the fine histogram.

5. The SPAD coarse-fine histogram synchronization quantization system based on pulse time interval weighting according to claim 4, characterized in that, The cyclic convolutional filtering circuit includes a data splicing unit, a convolution unit, and a weight storage unit; The data stitching unit is used to copy and stitch the thin histogram, and output the stitched thin histogram; The convolutional unit is used to convolve the stitched fine histogram and the weight coefficients pre-stored in the weight storage unit to output the denoised fine histogram. The weight storage unit is used to store the weight coefficients.

6. The SPAD coarse-fine histogram synchronization quantization system based on pulse time interval weighting according to claim 5, characterized in that, The peak calculation circuit includes: The first peak detection circuit is used to perform peak detection on the denoised fine histogram and output the peak position. An overflow detection circuit is used to compare the number of bins corresponding to the peak position with the number of bins in the fine histogram. If the number of bins corresponding to the peak position is greater than the number of bins in the fine histogram, an overflow flag is output. The peak position of the denoised fine histogram is then replaced with the difference between the number of bins corresponding to the peak position and the number of bins in the fine histogram to obtain the updated peak position of the denoised fine histogram.

7. A SPAD coarse-fine histogram synchronization quantization system based on pulse time interval weighting according to claim 6, characterized in that, The photon event coarse measurement module includes: The second time-to-digital conversion circuit is used to measure the second time interval between the photon triggering moment and the laser emission moment of the photon triggering event. A coarse histogram statistical circuit is used to statistically analyze the distribution characteristics of the second time interval between the photon triggering time and the laser emission time based on the weighted time interval, and output a coarse histogram.

8. A SPAD coarse-fine histogram synchronization quantization system based on pulse time interval weighting according to claim 7, characterized in that, The flight time calculation module includes: The second peak detection circuit is used to detect the peak position of the coarse histogram and output the highest peak position and the second highest peak position. An interval selection circuit is used to select the highest peak position or the second highest peak position as the target coarse measurement result based on the overflow flag; and to determine the target flight time based on the target coarse measurement result and the updated peak position of the denoised fine histogram.

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