Direct flight time information extraction method based on multistage quantization

Abstract

The invention discloses a direct flight time information extraction method based on multistage quantization, and belongs to the technical field of digital-analog hybrid integrated circuits, and the method comprises the steps: detecting a flight time signal through SPAD; performing coarse and fine two-stage quantitative recording through a shift register and an analog counter; quantizing the analog level into a digital signal by adopting a multi-stage quantization circuit and generating a flight time histogram; a window signal is generated based on the coarse quantization time-of-flight histogram, and time amplification is realized through a time-to-analog conversion and amplification circuit; and finally, based on the coarse quantization time-of-flight histogram and the fine quantization time-of-flight histogram, extracting the time-of-flight and calculating the distance. According to the invention, the precision is ensured, and the memory resource demand and the system power consumption are obviously reduced.

Description

Technical Field

[0001] This invention belongs to the field of mixed-signal integrated circuit technology, specifically relating to a method for extracting direct time-of-flight information based on multi-level quantization. Background Technology

[0002] Time-of-Flight (ToF) imaging is one of the core technologies in the field of 3D ranging imaging with lidar. Its basic principle is to emit modulated pulsed laser signals from a laser source towards the target in the field of view. After the laser is reflected by the target, it is received by a photoelectric sensor. By directly or indirectly measuring the flight time of the laser from emission to reception, and combining this with the speed of light, the distance between the sensor and the target is calculated, thereby reconstructing the target's three-dimensional spatial information. Direct Time-of-Flight (dToF) technology, with its advantages of wide ranging range and fast response speed, is widely used in consumer electronics, autonomous driving, and industrial inspection. Its core implementation method uses a single-photon avalanche diode (SPAD) as a photoelectric detection device to capture the flight time information of a single photon. A time-to-digital converter (TDC) converts the photon flight time into digital codewords, and histogram statistics are performed based on multiple detection results to generate a time-of-flight histogram. Finally, effective flight time information is extracted using algorithms such as peak detection to complete the ranging.

[0003] In direct time-of-flight imaging systems, the temporal resolution of the time-of-flight histogram determines the ranging accuracy, while the number of histogram bins affects the ranging distance. To achieve higher range resolution and measurable distance, the time quantization step size for each histogram bin needs to be reduced, and the number of histogram bins needs to be increased. This inevitably leads to an exponential increase in the amount of memory used to store histogram data. In existing technologies, histogram generation is mainly based on the digital domain, typically using static random access memory (SRAM) or parallelized digital counters to statistically store a large number of time-of-flight codewords. For example, when centimeter-level or even millimeter-level range resolution is required, the number of histogram bins often needs to reach thousands or even tens of thousands. In this case, SRAM needs to provide massive storage units to accommodate the count data of each histogram bin, and parallelized digital counters also need to be configured with a large number of counting modules. This not only leads to a sharp increase in the area occupied by the circuit chip but also significantly increases the power consumption of the system, severely restricting the application of dToF technology in miniaturized, low-power devices.

[0004] Meanwhile, direct time-of-flight ranging (DFT) technology has inherent limitations in improving resolution. The distance resolution of DFT directly depends on the time quantization accuracy of the time-of-flight measurement (TDC); that is, the smaller the quantization step size, the higher the theoretical ranging resolution. However, the quantization step size of traditional TDC is limited by the circuit's clock frequency, noise level, and manufacturing process. To further reduce the quantization step size to improve resolution, a more complex TDC architecture is required, which significantly increases the design difficulty, circuit complexity, and power consumption. On the other hand, reducing the quantization step size directly leads to a further increase in the number of histogram bins, not only exacerbating the pressure on memory resources but also diluting the effective signal in the histogram with more noise, reducing the signal-to-noise ratio (SNR) and consequently affecting the accuracy of extracting effective time-of-flight information. This vicious cycle of "resolution improvement - quantization step size reduction - surge in resource consumption - decrease in SNR" makes traditional DFT technology face a bottleneck that is difficult to overcome in the pursuit of high resolution. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a method for extracting direct time-of-flight information based on multi-level quantization. The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides a method for extracting direct time-of-flight information based on multi-level quantization, comprising: Step 1: Use SPAD and quenching reset circuit to detect photon signals and output time-of-flight pulse signals corresponding to the photon signal detection time and the laser emission start time interval; Step 2: Perform two-level quantization processing on the time-of-flight pulse signal, wherein: In the coarse quantization stage, the flight time pulse signal is coarsely quantized and recorded by a shift register and an analog counter, and the analog level signal of the analog counter is quantized in multiple stages to generate a coarse quantized flight time histogram. In the fine quantization stage, the peak position is determined according to the coarse quantization time-of-flight histogram and a window signal corresponding to the peak position is generated. The window signal and the time-of-flight pulse signal are amplified by a time-to-analog converter and a time-amplifier circuit. The amplified time signal is finely quantized and recorded by the shift register and the analog counter. The analog level signal of the analog counter is quantized in multiple stages to generate a fine quantization time-of-flight histogram. Step 3: Extract target flight time information based on the coarse-quantized flight time histogram and the fine-quantized flight time histogram, and calculate the ranging result.

[0006] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The direct time-of-flight information extraction method based on multi-level quantization of the present invention adopts a two-level strategy of first coarse quantization for positioning and then fine quantization for measurement. Combined with time amplification technology, it achieves high temporal resolution without relying on a high-frequency clock, thereby improving the overall quantization speed and system response capability. By using two-step time-of-flight quantization, it achieves high-precision ranging while reducing the amount of memory required to generate the time-of-flight histogram.

[0007] 2. The direct time-of-flight information extraction method based on multi-level quantization of the present invention utilizes a time-to-analog converter during the two-level quantization process to convert the time interval into the descent rate of the analog level at different multiples. A comparator then amplifies the time interval, thereby amplifying the time of flight and improving ranging accuracy. Furthermore, the amplification factor is adjustable, allowing for a flexible balance between resolution, speed, and power consumption according to application requirements, making it suitable for various scenarios from consumer electronics to industrial inspection.

[0008] In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent, preferred embodiments are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0009] Figure 1 This is a flowchart of a direct time-of-flight information extraction method based on multi-level quantization provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a shift register and analog counter used to record coarse-quantized flight time according to an embodiment of the present invention; Figure 3 This is a timing diagram of a shift register and analog counter for recording coarse-quantized flight time, provided in an embodiment of the present invention. Figure 4 This is a schematic diagram of a multi-level quantization analog counter scheme provided in an embodiment of the present invention; Figure 5 This is a timing diagram of a multi-level quantization analog counter scheme provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the structure of a time-to-analog converter and a time-to-amplifier circuit provided in an embodiment of the present invention; Figure 7 This is a timing diagram of a time-to-analog converter and time-to-amplifier circuit, a shift register and an analog counter for recording finely quantized flight time, provided by an embodiment of the present invention. Detailed Implementation

[0010] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following describes in detail a direct time-of-flight information extraction method based on multi-level quantization proposed according to the present invention, in conjunction with the accompanying drawings and specific embodiments.

[0011] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0012] This invention provides a method for extracting direct time-of-flight information based on multi-level quantization. Its core lies in combining two-level quantization with time amplification, significantly reducing storage resource requirements while maintaining accuracy. Please refer to... Figure 1 , Figure 1 This is a flowchart of a direct time-of-flight information extraction method based on multi-level quantization provided in an embodiment of the present invention, such as... Figure 1 The direct time-of-flight information extraction method based on multi-level quantization shown in this embodiment includes the following steps: Step 1: Use SPAD and quenching reset circuit to detect photon signals and output time-of-flight pulse signals corresponding to the photon signal detection time and the laser emission start time interval.

[0013] Step 2: Perform two-stage quantization on the time-of-flight pulse signal, where: In the coarse quantization stage, the flight time pulse signal is coarsely quantized and recorded by a shift register and an analog counter, and the analog level signal of the analog counter is quantized in multiple stages to generate a coarse quantized flight time histogram. In the fine quantization stage, the peak position is determined based on the coarse quantization time-of-flight histogram and a corresponding window signal is generated. The window signal and the time-of-flight pulse signal are amplified by a time-to-analog converter and a time amplifier circuit. The amplified time signal is then finely quantized and recorded by a shift register and an analog counter. The analog level signal of the analog counter is quantized in multiple stages to generate a fine quantization time-of-flight histogram. Step 3: Extract target flight time information based on coarse and fine flight time histograms, and calculate the ranging results.

[0014] In this embodiment, after extracting the target flight time information based on the coarse and fine time-of-flight histograms, the distance between the sensor and the target can be calculated by combining it with the speed of light.

[0015] Furthermore, the two-level quantization process of this embodiment will be described in detail.

[0016] In this embodiment, the shift register includes multiple cascaded D flip-flops, each D flip-flop being connected to an analog counter, and each D flip-flop corresponding to a time quantization interval. See also... Figure 2 , Figure 2 This is a schematic diagram of a shift register and analog counter recording coarse quantization flight time according to an embodiment of the present invention, as shown below. Figure 2 As shown, the shift register consists of multiple cascaded D flip-flops (DFFs). The input (D terminal) is connected to the output of the SPAD. The output (Q terminal) of each D flip-flop is simultaneously connected to the input of an AND gate and the input of the next D flip-flop. The CLK terminal of the D flip-flop is connected to the sampling clock. The other input of the AND gate is connected to the trigger signal, and the output is connected to the input of the analog counter (AC).

[0017] Specifically, in the coarse quantization stage, the time-of-flight pulse signal is coarsely quantized and recorded using a shift register and an analog counter, including: The time-of-flight pulse signal is input into the shift register. During the exposure stage, the sampling clock drives the shift register to record the position of the time-of-flight pulse signal on the time axis. After the exposure phase ends, the corresponding analog counter is triggered based on the bit that is "1" in the shift register, causing its count value to increase by 1; Multiple exposures are performed to accumulate the time-of-flight distribution in an analog counter, thus achieving coarse quantization recording.

[0018] Furthermore, combined Figure 3 The working process of the shift register and analog counter in the embodiments of the present invention will be described. Figure 3 This is a timing diagram of a shift register and analog counter recording coarse-quantized flight time according to an embodiment of the present invention, where #N represents the flight time of the Nth probe. Figure 3As shown, during time-of-flight measurement, the analog counter should be reset first. During the exposure phase, a sampling clock is connected to a fixed frequency clock. When the SPAD outputs (i.e., the output of the SPAD and the quenching reset circuit) a time-of-flight pulse signal, the shift register sets the output of the first D flip-flop to "1" under the action of the sampling clock, and performs a shift operation under the subsequent pulse of the sampling clock. After the exposure phase ends, the sampling clock is no longer connected, and the output of the shift register no longer changes. At this time, the number of bits x at the output of the shift register that are "1" should be the xth pulse signal sampled by the shift register from the SPAD output. Subsequently, a trigger signal pulse appears, and the count of the analog counter corresponding to the "1" at the output of the shift register increases by 1. After repeated exposures, the time-of-flight histogram is stored in the analog counter. The time resolution is entirely determined by the frequency of the sampling clock, which is numerically equivalent to the period of the sampling clock.

[0019] For example, such as Figure 3 As shown, the shift register has 8 bits. The sampling clock introduces a 100MHz clock signal with a total of 8 pulses. Taking the Nth detection flight time as an example, the SPAD output is sampled during the 2nd and 5th clock pulses of the sampling clock. Therefore, after the exposure is completed, the outputs of the 2nd and 5th bits of the shift register are set to "1". After the trigger signal pulse appears, the count of the corresponding analog counters numbered 2 and 5 increases by 1, and the count of the corresponding time-of-flight histogram bins numbered 2 and 5 increases by 1. The time resolution is 10 nanoseconds.

[0020] In this embodiment, the analog counter is a charge storage type counter, and its output voltage decreases linearly as the count value increases, satisfying the following relationship: ; in, The output voltage of the analog counter. This is the power supply voltage. The count value of the analog counter. This is the step size of the analog counter.

[0021] It should be noted that the shift register and the analog counter are multiplexed during the two-stage quantization process. In the coarse quantization stage and the fine quantization stage, after acquiring the analog level signal from the analog counter, the multiplexed multi-stage quantization circuit is then used to perform multi-stage quantization on the analog level signal from the analog counter.

[0022] In this embodiment, the multi-level quantization circuit includes a comparator and a digital counter, and the multi-level quantization process specifically includes: S1: In the first-level quantization, the output voltage of the analog counter is compared with the reference threshold voltage to determine its voltage range.

[0023] In this embodiment, the reference threshold voltage is taken as the high threshold voltage. And satisfy the following relationship: ; In the formula, This is the power supply voltage. It is a low threshold voltage.

[0024] S2: In the second-level quantization, the threshold voltage of the comparator is selected as the high threshold voltage based on the judgment result of the first-level quantization. or low threshold voltage ; S3: Input a fixed frequency clock to both the analog counter and the digital counter simultaneously. The analog counter discharges under the clock drive, and the digital counter counts the clock pulses. S4: When the output voltage of the analog counter is lower than the selected threshold voltage, the comparator flips to stop the digital counter from counting. S5: Calculate the actual count value of the analog counter based on the selected threshold voltage and the count value of the digital counter.

[0025] In this embodiment, the actual count value of the analog counter is calculated as follows: If the comparator's threshold voltage is selected as the high threshold voltage ,but ; If the comparator's threshold voltage is selected as the low threshold voltage ,but ; In the formula, This is the actual count value of the analog counter. This is the count value of the digital counter. This is the step size of the analog counter.

[0026] Furthermore, combined Figure 4 and Figure 5 The circuit structure and operation process of the multi-level quantization in this embodiment will be described.

[0027] Please see Figure 4 , Figure 4 This is a schematic diagram of a multi-level quantization analog counter scheme provided by an embodiment of the present invention. Figure 4 As shown, Figure 4 The analog counter in Figure 2 The analog counters shown are the same, and their input terminal V in Based on the exposure and quantization stages, the time-of-flight information input and fixed-frequency clock input are connected respectively. The reset terminal RST receives a pulse before the exposure stage. The comparator's V- terminal is connected to the output terminal V of the analog counter. out V+ The terminal is connected to the output of a 2-to-1 multiplexer; the two input terminals of the 2-to-1 multiplexer are respectively connected to the high threshold voltage. and low threshold voltage The selection signal is affected by the comparator output; the digital counter's reset terminal RST receives a pulse before the quantization stage, the input terminal CLK receives a fixed-frequency clock at the same frequency as the analog counter's input during the quantization stage, and the stop terminal STOP is connected to the comparator's output.

[0028] Please see Figure 5 , Figure 5 This is a timing diagram of a multi-level quantization analog counter scheme provided in an embodiment of the present invention. For example... Figure 5 As shown, during the exposure phase, the analog counter records the time-of-flight information after being reset, and the output level decreases accordingly. After the exposure phase ends and before the quantization phase begins, the digital counter is reset, and simultaneously, the output voltage of the analog counter... Compared with the reference threshold voltage (high threshold voltage) ) for comparison, It should be the power supply voltage. With low threshold voltage Half of the sum, if Greater than In the quantization stage, the comparator uses a high threshold voltage. Conversely, a low threshold voltage is used. After the quantization phase begins, a fixed-frequency clock is simultaneously input to both the analog counter and the digital counter. The output voltage of the analog counter... As the influence of the input clock decreases, the digital counter continues counting. When the voltage drops below the selected comparator threshold voltage, the comparator output toggles, causing the digital counter to stop counting. The analog counter's count is determined by using a higher threshold voltage than the comparator's threshold voltage. The time should be The difference between the count value and the count value of the digital counter is used at the comparator threshold voltage using the low threshold voltage. The time should be The difference between the count value and the count value of the digital counter, where, This is the step size of the analog counter.

[0029] For example, such as Figure 5 As shown, , When quantizing the analog counter for the first frame, the analog counter counts to 6. Before the quantization phase begins, The comparator threshold voltage is selected as the high threshold voltage. During the quantization phase, when the digital counter counts to 2, the comparator flips, causing the digital counter to count to 2. The final quantization result for the analog counter is 8 – 2 = 6. When quantizing the first frame's analog counter, the analog counter count is 11. Before the quantization phase begins... The comparator threshold voltage is selected as the low threshold voltage. During the quantization phase, when the digital counter counts to 5, the comparator flips, causing the digital counter to count to 2. The final quantization result of the analog counter is 16 – 5 = 11.

[0030] The multi-level quantization analog counter scheme used in this embodiment can convert the analog level signal of the analog counter into a digital signal more quickly.

[0031] In this embodiment, after the coarse quantization stage, a coarse quantization time-of-flight histogram is obtained. Upon entering the fine quantization stage, a phase detector is first used to analyze the coarse quantization time-of-flight histogram to determine the peak position. A window signal is generated based on a preset window width, centered on the time corresponding to the peak position. This window signal corresponds to the time period near the peak in the coarse quantization histogram on the time axis. Next, time amplification is performed using a time-to-analog converter and a time amplification circuit. Then, fine quantization recording and multi-level quantization are performed using a multiplexed shift register, an analog counter, and a multi-level quantization circuit, finally yielding the fine quantization time-of-flight histogram.

[0032] Specifically, the time magnification process includes the following steps: Step a: Use a time-to-analog converter to convert the window signal and the time-of-flight pulse signal into analog level signals corresponding to their time interval; Step b: Input the analog level signal into the time amplifier circuit, and amplify the time by adjusting the capacitance ratio and current ratio of the time amplifier circuit to obtain the amplified time signal.

[0033] Furthermore, combined Figure 6 The structure and time amplification process of the time analog converter and time amplifier circuit in this embodiment will be described. Figure 6 This is a schematic diagram of the structure of a time-to-analog converter and a time-to-amplifier circuit provided in an embodiment of the present invention, as shown below. Figure 6 As shown, the time amplifier circuit includes: a first capacitor, a first current source, a second capacitor, a second current source, and a comparator, wherein the capacitance of the second capacitor is equal to that of the first capacitor. The current value of the second current source is times that of the first current source. The first capacitor and the first current source are used to generate a corresponding first analog voltage signal based on the time interval between the window signal and the time-of-flight pulse signal; the comparator is used to output a flip signal when the voltage of the second capacitor drops to a preset threshold, and the time of the flip signal is amplified relative to the original time interval. The amplification factor is times. That is, in this embodiment, the amplification factor of the time amplifier circuit. It can be represented as: , This is the capacitance proportionality coefficient. This is the current proportionality coefficient.

[0034] Specifically, such as Figure 6 As shown, after the fine-quantization time-of-flight measurement begins, the window signal is provided by the phase detector. Based on the results of the coarse-quantization histogram, a pulse appears at a determined location, V. out1 It begins to descend and stops after SPAD outputs, V out1 The decreasing level can be considered as the time interval between the window signal and the SPAD output. After each fine-quantization time-of-flight measurement, a pulse appears in the conversion signal, V. out2 It begins to decrease because the connected capacitor is V. out1 of The current source is only V. out2 of Therefore, the descent speed is V. out1 of The time interval between the comparator flipping and the appearance of the conversion signal pulse is equal to the time interval between the window signal pulse and the SPAD output. This multiplier amplifies the time frame.

[0035] Please see Figure 7 , Figure 7 This is a timing diagram of a time-to-analog converter and time-amplifier circuit, a shift register and an analog counter for recording finely quantized flight time, provided in an embodiment of the present invention. Figure 7 As shown, the shift register's input at this time is the comparator's output, and it only retains one bit for recording when the comparator's output is high. Simultaneously with the pulse of the conversion signal, a fixed-frequency clock is connected to the sampling clock, and the shift register samples the comparator's output. During this stage, the sampling clock samples the data for time amplification. The result after doubling the time resolution is now 1 / 3 of the sampling clock period. In other words, the time resolution of the fine quantization stage is equal to that of the coarse quantization stage. There has been a significant improvement.

[0036] For example, such as Figure 7 As shown, at this time , The time interval between the window signal and the SPAD output is 8 nanoseconds, and the sampling clock period is 10 nanoseconds. out2 When the descent time reaches 64 nanoseconds, the comparator output flips, which is captured by the shift register during the 6th sampling clock pulse. After the sampling clock pulse ends, the 3rd bit, which ultimately outputs a "1", is counted by the analog counter numbered 6. This improves the time resolution of the coarse quantization stage from 10 nanoseconds to 1.25 nanoseconds, enhancing the time resolution and enabling fine quantization of the time of flight.

[0037] The direct time-of-flight information extraction method based on multi-level quantization in this invention employs a two-stage strategy: first, coarse quantization for positioning, and then fine quantization for precise measurement. Combined with time amplification technology, it achieves high temporal resolution without relying on a high-frequency clock, thus improving overall quantization speed and system response capability. By using two-step time-of-flight quantization, it achieves high-precision ranging while reducing the amount of memory required for generating the time-of-flight histogram.

[0038] 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.

[0039] 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.

[0040] 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 direct time-of-flight information based on multi-level quantization, characterized in that, include: Step 1: Use SPAD and quenching reset circuit to detect photon signals and output time-of-flight pulse signals corresponding to the photon signal detection time and the laser emission start time interval; Step 2: Perform two-level quantization processing on the time-of-flight pulse signal, wherein: In the coarse quantization stage, the flight time pulse signal is coarsely quantized and recorded by a shift register and an analog counter, and the analog level signal of the analog counter is quantized in multiple stages to generate a coarse quantized flight time histogram. In the fine quantization stage, the peak position is determined according to the coarse quantization time-of-flight histogram and a window signal corresponding to the peak position is generated. The window signal and the time-of-flight pulse signal are amplified by a time-to-analog converter and a time-amplifier circuit. The amplified time signal is finely quantized and recorded by the shift register and the analog counter. The analog level signal of the analog counter is quantized in multiple stages to generate a fine quantization time-of-flight histogram. Step 3: Extract target flight time information based on the coarse-quantized flight time histogram and the fine-quantized flight time histogram, and calculate the ranging result.

2. The direct time-of-flight information extraction method based on multi-level quantization according to claim 1, characterized in that, In the coarse quantization stage, the time-of-flight pulse signal is coarsely quantized and recorded using a shift register and an analog counter, including: The time-of-flight pulse signal is input into the shift register, wherein the shift register includes multiple cascaded D flip-flops, each D flip-flop is connected to an analog counter, and each D flip-flop corresponds to a time quantization interval; During the exposure stage, the shift register is driven by a sampling clock to record the position of the time-of-flight pulse signal on the time axis; After the exposure stage is completed, the analog counter at the corresponding position is triggered to increment its count value by 1 based on the bit that is "1" in the shift register; Multiple exposures are performed, and the time-of-flight distribution is accumulated in the analog counter to achieve coarse quantization recording.

3. The direct time-of-flight information extraction method based on multi-level quantization according to claim 1, characterized in that, The analog counter is a charge storage type counter, and its output voltage decreases linearly as the count value increases, satisfying the following relationship: ； in, The output voltage of the analog counter. This is the power supply voltage. The count value of the analog counter. The step size of the analog counter is given.

4. The direct time-of-flight information extraction method based on multi-level quantization according to claim 1, characterized in that, In the coarse quantization and fine quantization stages, a multi-stage quantization circuit is used to perform multi-stage quantization on the analog level signal of the analog counter. The multi-stage quantization circuit includes a comparator and a digital counter. The multi-stage quantization process includes: In the first-level quantization, the output voltage of the analog counter is compared with the reference threshold voltage to determine its voltage range; In the second-level quantization, the threshold voltage of the comparator is selected as the high threshold voltage based on the result of the first-level quantization. or low threshold voltage ; A fixed-frequency clock is simultaneously input to the analog counter and the digital counter. The analog counter discharges under the clock drive, and the digital counter counts the clock pulses. When the output voltage of the analog counter is lower than the selected threshold voltage, the comparator flips to stop the digital counter from counting. The actual count value of the analog counter is calculated based on the selected threshold voltage and the count value of the digital counter.

5. The direct time-of-flight information extraction method based on multi-level quantization according to claim 4, characterized in that, The reference threshold voltage is set to the high threshold voltage. And satisfy the following relationship: ； In the formula, This is the power supply voltage. It is a low threshold voltage.

6. The direct time-of-flight information extraction method based on multi-level quantization according to claim 5, characterized in that, The actual count value of the analog counter is calculated as follows: If the threshold voltage of the comparator is selected as the high threshold voltage ,but ; If the threshold voltage of the comparator is selected as the low threshold voltage ,but ; In the formula, This is the actual count value of the analog counter. The count value of the digital counter. The step size of the analog counter is given.

7. The direct time-of-flight information extraction method based on multi-level quantization according to claim 1, characterized in that, In the fine quantization stage, a phase detector is used to analyze the coarse quantization time-of-flight histogram to determine the peak position, and a window signal is generated based on the corresponding time of the peak position and a preset window width.

8. The method for extracting direct time-of-flight information based on multi-level quantization according to claim 1, characterized in that, The time magnification process includes: The time-to-analog converter is used to convert the window signal and the time-of-flight pulse signal into analog level signals corresponding to the time interval between them; The analog level signal is input into the time amplifier circuit, and time amplification is achieved by adjusting the capacitance ratio and current ratio of the time amplifier circuit to obtain the amplified time signal.

9. The method for extracting direct time-of-flight information based on multi-level quantization according to claim 1, characterized in that, The time resolution of the fine quantization stage is the same as the time resolution of the coarse quantization stage. ,in, This is the capacitance proportionality coefficient. This is the current proportionality coefficient.

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