Laser radar system-based ranging method

Abstract

The application provides a laser radar system and a ranging method. The laser radar system comprises: a timing control module, configured to generate a laser trigger signal and a start timing signal; a laser emitting unit, configured to emit a laser pulse in response to the laser trigger signal; a return signal receiving unit, configured to receive a return signal and generate a stop timing signal; a clock source, configured to generate a reference clock; a clock generation module, configured to generate a plurality of reference clocks with the same frequency and a fixed phase difference; and a histogram time-to-digital converter group, comprising a plurality of histogram time-to-digital converters, each of which is connected to one reference clock; and each histogram time-to-digital converter is configured to receive the start timing signal and the stop timing signal and generate histogram data. The laser radar system and the ranging method can multiply the distance resolution of the laser radar under the condition that the system main frequency or the device performance is limited.

Description

Technical Field

[0001] This application relates to the field of lidar distance detection technology, and in particular to a ranging method based on a lidar system. Background Technology

[0002] LiDAR plays a crucial role in high-precision environmental perception, elevation imaging, and modeling. The emergence of single-photon avalanche diodes (SPADs) has significantly improved LiDAR sensors and imaging technology. A SPAD is a special type of photodiode that operates in Geiger mode when its operating voltage exceeds the avalanche breakdown voltage, achieving extremely high sensitivity and the ability to detect single photons, thus possessing photon-level detection sensitivity. LiDAR systems using SPADs can achieve high-precision 3D imaging under weak light signal conditions, greatly enhancing LiDAR's long-range detection and target imaging capabilities in complex environments. Furthermore, array-type devices composed of two-dimensionally integrated SPAD devices, as a type of area array imaging sensor, not only possess the advantages of high sensitivity and high ranging accuracy of SPADs but also gain high ranging speed and high pixel resolution. Therefore, LiDAR technology based on SPAD arrays can solve the problems of high cost, complex data processing, and susceptibility to environmental influences inherent in traditional LiDAR.

[0003] The imaging technology used in LiDAR systems employing SPAD arrays is generally the direct time-of-flight (dToF) method. Its basic principle is that the system illuminates the target object with laser pulses, which reflect the pulses. This echo signal is received by the system's sensor. The system calculates the time difference between emission and reception—the time of flight—to determine the distance from the sensor to the target. A typical dToF LiDAR system consists of a light source, a sensor, a timing circuit, and a signal processing component. The light source emits short laser pulses, the sensor captures photons reflected from the scene, the timing circuit measures the time of flight of each detected photon, and the signal processing component converts the raw data into distance information. Combined with scanning technology, this type of system can generate point clouds for the target object and construct a 3D surface structure map of the scene using specific algorithms. Because the dToF method can sense farther distances at high peak power while maintaining lower average power to meet human eye safety limitations, and because it offers fast response, accurate timing, and is mature and simple, it is currently widely used in LiDAR systems.

[0004] From a technical perspective, since the emission time of the laser signal is controllable, and the SPAD device, acting as a sensor, can output a pulse signal at any time, the ability to accurately measure the arrival time of the pulse signal becomes crucial to ranging accuracy. As the device for detecting the arrival time of the pulse signal, the minimum resolution of the time-to-digital converter (TDC) significantly impacts ranging accuracy. Currently used TDC technologies are heavily reliant on the system clock; with insufficient clock frequencies, TDC often fails to meet the requirements for high-precision ranging. Using processing chips with high-frequency clocks would greatly increase system costs. Therefore, it is necessary to research a TDC technology that can improve accuracy on systems with lower clock frequencies.

[0005] Due to the randomness of single-photon detectors' response to photon events and the binarized output characteristics of these detectors, SPAD-based lidar struggles to accurately determine target distance using single pulses or single cycles. Furthermore, signal-irrelevant photons from background illumination and noise signals from SPAD dark counting also contribute. To improve the signal-to-noise ratio, a common approach is time-correlated single photon counting (TCSPC). The core of this technique is the Monte Carlo method: the SPAD device at the receiver acquires photon information and sends it in pulses to a time-to-digital converter (TDC). After the TDC converts the photon time information, it accumulates the photon counts over multiple cycles along the time dimension, generating a histogram of photon time distribution. By analyzing the accumulated histogram data, noise and signal can be quickly and effectively distinguished, the target's actual flight time obtained, and the distance information converted from this data. The key to this technology lies in the design of the TDC device. The basic principle of TDC is to compare the measured time with a reference clock and calculate the time difference.

[0006] For the Time Difference Detection (TDC) devices used in SPAD devices, the main operating method currently is based on a counter. The principle of a counter-based TDC is that by controlling the start and stop of the counter-type TDC, the counter can calculate the time difference from signal transmission to the reception of the echo pulse. The TDC then accumulates the data in the corresponding time unit stored in memory. After measurement, a "time unit - photon count" histogram can be directly generated for subsequent processing. The principle and structure of the counter-type TDC are relatively simple, but its accuracy is highly dependent on the clock frequency. Methods to improve the accuracy of counter-type TDC technology generally involve using a high-speed clock signal generator, such as a phase-locked loop (PLL), to provide a sufficiently high operating frequency for the TDC counter to achieve a very small measurement resolution. However, when the system's main frequency is limited, high-speed clock signal generators cannot reach high frequencies, and the TDC resolution will not meet the requirements for high-precision ranging.

[0007] In addition, there are designs for high-precision TDC modules based on buffers. These designs typically employ delay chains or phase-locked loops (PLLs). By controlling their start and stop, they utilize the extremely short delays of the buffer devices within the delay chain or PLL ring oscillator to achieve high-resolution timing. The timing data can be obtained from the output taps of the buffers in the delay line or PLL ring oscillator. After certain calculations, the time difference can be calculated. However, the resolution of these high-precision TDC modules is very small. To achieve a large range, a large number of buffers must be designed. Therefore, buffer-based high-precision TDCs are generally combined with counter-type TDCs, using interpolation timing methods for time difference measurement: the high-precision TDC operates within the timing cycle of the counter-type TDC, allowing the calculation of signal times that are ahead of and behind the effective edge of CLK. After timing ends, the interpolation calculation combines the two data to obtain the final TDC data. This method still requires a long buffer chain, and the buffer delay is easily affected by temperature and voltage and produces a certain degree of distortion. Slight distortion will be amplified to a more serious degree when multiple buffers are connected in series. Combining high-precision TDC and counter-type TDC also increases the design difficulty of the control circuit and ultimately increases the cost of the lidar system. Summary of the Invention

[0008] In view of the shortcomings of the prior art described above, the purpose of this application is to provide a ranging method based on a lidar system, which can significantly improve the distance resolution of lidar even when the system frequency or device performance is limited.

[0009] In a first aspect, this application provides a lidar system, comprising:

[0010] The timing control module is used to generate laser trigger signals and start timing signals;

[0011] A laser emitting unit is used to respond to the laser trigger signal and emit laser pulses;

[0012] The echo receiving unit is used to receive the echo signal and generate a stop timing signal;

[0013] Clock source, used to generate a reference clock;

[0014] A clock generation module is used to receive the reference clock and generate multiple reference clocks with the same frequency and a fixed phase difference.

[0015] The histogram time-to-digital converter group includes multiple histogram time-to-digital converters, each of which is connected to a reference clock; each histogram time-to-digital converter is used to receive the start timing signal and the stop timing signal, and generate histogram data based on the time difference between the two.

[0016] In one implementation of the first aspect, the histogram time-to-digital converter includes:

[0017] A counter is used to record the number of clock cycles between the start timing signal and the stop timing signal;

[0018] Multiple time unit registers are provided, with one time unit register corresponding to each clock cycle number. When the counter receives the stop timing signal once, the value in the time unit register corresponding to the clock cycle number is incremented by one.

[0019] In one implementation of the first aspect, the clock generation module is configured to: receive the reference clock, perform frequency multiplication on the reference clock to obtain a frequency multiplied clock, and delay the frequency multiplied clock to generate multiple reference clocks, each reference clock having the same frequency and a fixed phase difference.

[0020] In one implementation of the first aspect, the clock generation module employs a phase-locked loop circuit or a delay chain of an FPGA.

[0021] Secondly, this application provides a ranging method, the ranging method comprising:

[0022] A set of histogram data is generated using the aforementioned lidar system;

[0023] Generate equivalent histogram data based on the aforementioned set of histogram data;

[0024] The flight time of the laser pulse is calculated based on the equivalent histogram data.

[0025] The distance is calculated based on the flight time of the laser pulse and the speed of light.

[0026] In one implementation of the second aspect, generating equivalent histogram data based on the set of histogram data includes:

[0027] The number of equivalent time units in the equivalent histogram data is calculated based on the number of histogram time-to-digital converters in the same histogram time-to-digital converter group and the number of time units in the histogram data.

[0028] The equivalent clock period of the equivalent time unit in the equivalent histogram data is calculated based on the clock period of the reference clock and the number of histogram time-to-digital converters in the same histogram time-to-digital converter group.

[0029] Based on the photon counts of each time unit in each histogram data, calculate the equivalent photon counts of each equivalent time unit in the equivalent histogram data.

[0030] In one implementation of the second aspect, the calculation of the number of equivalent time units in the equivalent histogram data based on the number of histogram time-to-digital converters in the same histogram time-to-digital converter group and the number of time units in the histogram data is performed using the following formula:

[0031]

[0032] in, The number of equivalent time units;

[0033] The number of time units in the histogram data;

[0034] This represents the number of histogram time-to-digital converters in the same histogram time-to-digital converter group.

[0035] In one implementation of the second aspect, the equivalent clock period of the equivalent time unit in the equivalent histogram data is calculated based on the clock period of the reference clock and the number of histogram time-to-digital converters in the same histogram time-to-digital converter group, using the following calculation formula:

[0036]

[0037] in, The equivalent clock period for an equivalent time unit;

[0038] The clock period of the reference clock;

[0039] This represents the number of histogram time-to-digital converters in the same histogram time-to-digital converter group.

[0040] In one implementation of the second aspect, the equivalent photon count of each time unit in the equivalent histogram data is calculated based on the photon count of each time unit in each histogram data, using the following calculation formula:

[0041] for :

[0042]

[0043] for ,

[0044]

[0045] for ,

[0046]

[0047] Where i is the sequence number of the equivalent time unit;

[0048] n is the number of histogram time-to-digital converters in the same histogram time-to-digital converter group;

[0049] It is a positive integer;

[0050] It is an integer, and ;

[0051] For the first Equivalent photon count for each equivalent time unit;

[0052] The first in the same histogram time-to-digital converter group The first histogram data of the time-to-digital converter Photon count per time unit;

[0053] The first in the same histogram time-to-digital converter group The first histogram data of the time-to-digital converter Photon count per time unit.

[0054] In one implementation of the second aspect, calculating the time of flight of the laser pulse based on the equivalent histogram data includes:

[0055] The time unit number of the echo signal is determined based on the equivalent histogram data.

[0056] The flight time of the laser pulse is obtained based on the time unit number of the echo signal and the equivalent clock period.

[0057] As described above, this application provides a ranging method based on a lidar system, which can significantly improve the range resolution of lidar even when the system's main frequency or device performance is limited. Attached Figure Description

[0058] Figure 1 The diagram shown is a schematic of a single-pixel lidar system according to an embodiment of this application.

[0059] Figure 2 The example shown is implemented using a delay chain in one embodiment of this application. Figure 1 Schematic diagram of the clock generation module.

[0060] Figure 3 The example shown is implemented using a combination of a phase-locked loop circuit and a delay chain in one embodiment of this application. Figure 1 Schematic diagram of the clock generation module.

[0061] Figure 4 The diagram shown is a schematic of a multi-pixel lidar system according to an embodiment of this application.

[0062] Figure 5 Displayed as Figure 3 Schematic diagram of the clock generation module.

[0063] Figure 6 The diagram shown is a schematic of a multi-pixel lidar system employing a multiplexer in one embodiment of this application.

[0064] Figure 7 The diagram shown is a schematic of a histogram time-to-digital converter shared by multiple sensors through a multiplexer in one embodiment of this application.

[0065] Figure 8 The flowchart shown is a distance measurement method according to an embodiment of this application.

[0066] Figure 9 Displayed as Figure 8 The detailed flowchart of step S200.

[0067] Figure 10 Displayed as Figure 8 The schematic diagram of step S200.

[0068] Figure 11 Displayed as Figure 8 The detailed flowchart of step S300. Detailed Implementation

[0069] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, unless otherwise specified, the following embodiments and features in the embodiments can be combined with each other.

[0070] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. Therefore, the drawings only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0071] The lidar system and ranging method of this embodiment will be described in detail below, so that those skilled in the art can understand the lidar system and ranging method of this embodiment without creative effort.

[0072] Please refer to Figure 1 This embodiment provides a lidar system for single-point ranging. The lidar system includes a timing control module, a laser emitting unit, an echo receiving unit, a clock source, a clock generating module, and a histogram time-to-digital converter group.

[0073] The timing control module generates the laser trigger signal and the start timing signal (Start). The laser emitting unit responds to the laser trigger signal and emits laser pulses. The echo receiving unit receives the echo signal and generates the stop timing signal (Stop). The clock source generates a reference clock. The clock generation module receives the reference clock and generates multiple reference clocks (reference clock 1, reference clock 2, ..., reference clock n) with the same frequency and a fixed phase difference. The histogram time-to-digital converter group includes multiple histogram time-to-digital converters (Histo-TDC1, Histo-TDC2, ..., Histo-TDCn), each connected to one reference clock (reference clock 1 connected to Histo-TDC1, reference clock 2 connected to Histo-TDC2, and reference clock n connected to Histo-TDCn). Each histogram time-to-digital converter receives the start and stop timing signals and generates histogram data based on the time difference between them.

[0074] This embodiment uses multiple existing histogram time-to-digital converters with lower prices, lower clock speeds, and lower time accuracy to form a virtual histogram time-to-digital converter with higher time accuracy. This makes the time accuracy of the equivalent histogram data consistent with that of the corresponding high-clock-speed, high-precision time-to-digital converter, thereby reducing costs. Furthermore, it is implemented through pure digital circuitry, which improves anti-interference capabilities.

[0075] In one embodiment, each histogram time-to-digital converter in the histogram time-to-digital converter group includes a counter and multiple time unit registers (Reg1, Reg2, Reg3...RegL). The counter is used to record the number of clock cycles from the start timing signal to the stop timing signal; each clock cycle corresponds to one time unit register; when the counter receives a stop timing signal, the value in the time unit register corresponding to the clock cycle number is incremented by one.

[0076] In one embodiment, after receiving a Stop signal, the counter latches the value of the number of clock cycles. The address decoding logic unit decodes the value of the number of clock cycles into the address of the time unit register, and then performs read, increment, and write operations on the value in the time unit register according to the address.

[0077] A clock source is used to provide the system clock signal. In one embodiment, the clock signal is generated by an external crystal oscillator and input to the programmable logic unit. In another embodiment, the clock signal is provided directly by an external clock signal generator. The external crystal oscillator can be a passive crystal, which needs to work in conjunction with the oscillation circuit inside the programmable logic unit; or it can be an active crystal oscillator that can directly output the clock signal.

[0078] In one embodiment, the echo receiving unit includes a photoelectric sensor, a sensor driving circuit, and a signal processing circuit.

[0079] Photoelectric sensors are used to convert received echo signals into electrical pulse signals; they are semiconductor devices with single-photon detection capabilities, such as single-photon avalanche diodes (SPADs), and can be configured as single-pixel, one-dimensional linear array, or two-dimensional array structures according to system requirements.

[0080] The sensor driving circuit is electrically connected to the photoelectric sensor, providing it with the bias voltage, quenching control, and reset timing required for normal operation. It also responds to the enable signal output by the timing control module in the main control unit, enabling precise scheduling of the photoelectric sensor's operating state. The sensor driving circuit is used to enable single-photon detectors such as SPADs to operate normally. For example, for SPADs, the sensor driving circuit typically provides a reverse bias (Geiger mode) higher than the breakdown voltage, rapidly quenches the current after an avalanche, and resets upon readiness. The sensor driving circuit can be implemented using existing technology, such as a dedicated driver chip or discrete components; the structure of the sensor driving circuit itself is not the focus of this invention.

[0081] The signal processing circuit is integrated inside the programmable logic unit. Its input is coupled to the output of the sensor driving circuit. It is used to shape and broaden the asynchronous narrow electrical pulse signal output by the driving circuit to generate a STOP event signal with a pulse width that can be stably captured by subsequent digital circuits, but whose rising edge (i.e., the effective time) reflects the arrival time of the original photon.

[0082] In one embodiment, the lidar system further includes a mechanical scanning device. The mechanical scanning device is used to implement the mechanical scanning function of the lidar, for example, by using a turntable to control the transmission / reception direction of the photoelectric sensors in the laser emitting unit and echo receiving unit, or by using rotating mirrors, galvanometers, or prisms to adjust the direction of the emitted laser. The scanning function of the mechanical scanning device is controlled by a timing control module.

[0083] In one embodiment, the lidar system further includes a data processing module. The timing control module controls the operation of the data processing module. When the data processing module operates, it retrieves register data (i.e., histogram data of each Histo-TDC) from the histogram time-to-digital converter group. Then, it converts the histogram data from each histogram in the same histogram time-to-digital converter group into a high-precision equivalent histogram. Finally, it uses peak-finding algorithms, such as direct peak finding, centroid peak finding, or Gaussian function fitting, to find the peak value in the virtual histogram. The flight time corresponding to the peak value is then used as the actual measured flight time value.

[0084] In one embodiment, the lidar system further includes an interface. The interface is used to send the measured time-of-flight of the laser pulses to a host computer. The interface is also used to receive commands from the host computer or to send lidar system information to the host computer.

[0085] In one embodiment, the clock generation module is configured to: receive a reference clock, perform frequency multiplication on the reference clock to obtain a frequency multiplied clock, and delay the frequency multiplied clock to generate multiple reference clocks, each reference clock having the same frequency and a fixed phase difference.

[0086] In one embodiment, the clock generation module employs a phase-locked loop (PLL) circuit to directly generate a reference clock with a fixed phase difference.

[0087] refer to Figure 2 In one embodiment, the clock generation module employs a delay chain of an FPGA. For example, the reference clock 2 of Histo-TDC2 is phase-delayed compared to the reference clock 1 of Histo-TDC1. The reference clock 3 of Histo-TDC3 is phase-delayed compared to the reference clock 2 of Histo-TDC2. And so on.

[0088] refer to Figure 2 A delay chain is a timing processing structure composed of multiple cascaded delay units. Each delay unit introduces a predetermined time delay into the input signal, and the delay units are cascaded sequentially, allowing the delay time to accumulate stage by stage as the signal propagates along the delay chain. When the input signal is a frequency-doubled clock, the delay chain structure can be used to delay the frequency-doubled clock, obtaining reference clocks with different time offsets from the outputs of different stages of the delay chain, thus forming a multi-phase reference clock.

[0089] refer to Figure 3 In one embodiment, the clock generation module employs a phase-locked loop (PLL) circuit and a delay chain structure to generate a multi-phase reference clock. The PLL circuit generates multiple reference clocks with predetermined phase differences based on a frequency-multiplied clock, and the delay chain structure further introduces a time delay into the reference clocks output by the PLL circuit to obtain a multi-phase reference clock that meets preset phase relationship requirements.

[0090] In this embodiment, when the phase offset granularity provided by the phase-locked loop circuit is limited and it is difficult to directly generate a reference clock with the required phase relationship, the delay chain structure is used to refine the delay of the reference clock, thereby achieving more flexible phase adjustment. Thus, the characteristics of the phase-locked loop circuit and the delay chain structure can be combined to generate multiple reference clocks with the same frequency and a fixed phase difference.

[0091] In this invention, the multi-phase reference clock signals generated by the clock generation module have the same frequency and exhibit a predetermined phase difference relationship in the time dimension. The phase difference can be characterized by a time offset, and the time offset is equivalent to the phase offset of the clock signal.

[0092] In one embodiment, the period of the multi-phase reference clock signal is assumed to be... The multi-phase reference clock signals are set at equal time intervals, and the time offset between adjacent multi-phase reference clock signals is... , Reference signal period of Divide into equal parts, thus forming The time offsets of the multi-phase reference clock signals with the same frequency and equal phase intervals are as follows: .

[0093] It should be understood that the aforementioned multi-phase reference clock signals with equal time intervals can be implemented using a phase-locked loop (PLL) circuit, a delay chain structure, or a combination of a PLL circuit and a delay chain structure. By configuring the PLL circuit and / or the delay chain structure, the number of multi-phase reference clock signals and their time offsets can be made to meet system requirements.

[0094] Please refer to Figure 4 This embodiment provides a lidar system for high-speed area array imaging. In this lidar system, the echo receiving unit includes a linear array or area array SPAD sensor, a corresponding multi-channel sensor driving circuit, and subsequent signal processing logic. The system is configured with multiple histogram time-to-digital converter groups, sufficient to allow each histogram time-to-digital converter group to be connected one-to-one, continuously to a pixel output channel of the sensor.

[0095] Please refer to Figure 5 All histogram time-to-digital converters (TDCs) share the same set of multi-phase reference clocks provided by the clock generation module and are subject to unified timing control. The data processing module can access data from all TDC modules in parallel, synchronously generating distance information for multiple points to achieve high frame rate imaging.

[0096] In some embodiments, the lidar system employs a one-dimensional linear array or a two-dimensional area array SPAD sensor to measure target surfaces with large areas. In this case, the number of SPAD pixels may exceed the number of multi-channel multi-phase TDC modules that the lidar system can provide, or allocating corresponding multi-channel multi-phase TDC modules to all output channels of the SPAD pixels will greatly increase the system cost.

[0097] Please refer to Figure 6 To address situations with a large number of pixels or limited system logic resources, this embodiment provides a low-cost lidar system. The signal processing circuit of the echo receiving unit in this lidar system includes a multiplexer. The multiplexer time-division multiplexes the output channels of multiple pixels to a set of histogram time-to-digital converters. A timing control module controls the channel selection of the multiplexer. The system iterates through all pixels via multiple time-varying measurement cycles, and finally, the main control unit reconstructs the distance information of the entire array. This embodiment significantly reduces system complexity and cost while maintaining high-precision ranging capabilities.

[0098] Please refer to Figure 7 In this embodiment, the pixel outputs of two sensors are connected to a multiplexer. The system needs to allocate m / 2 multi-phase Histo-TDC modules for m pixel sensors, which is equivalent to saving half the number of logic units.

[0099] In one embodiment, the lidar system uses a scanning method for measurement, and the target surface corresponding to the SPAD pixels in its receiving device will continuously move. In another embodiment, the lidar measures a moving target object. In both embodiments, during the repeated measurement of a specific area of ​​the target, because the entire repeated measurement process requires a very short time and the displacement distance of the target surface during the repeated measurement is very small, it can be assumed that the target object does not move relative to the lidar system within the extremely short time required for measurement, and the position being detected by the lidar does not move relative to the target object.

[0100] Please refer to Figure 8 This embodiment also provides a ranging method, which includes:

[0101] Step S100: Generate a set of histogram data using the lidar system of the above embodiment;

[0102] Step S200: Generate equivalent histogram data based on a set of histogram data;

[0103] Step S300: Calculate the flight time of the laser pulse based on the equivalent histogram data;

[0104] Step S400: Calculate the distance based on the flight time of the laser pulse and the speed of light.

[0105] In this embodiment, in a set of histogram time-to-digital converters, the phase difference of the reference clocks of two adjacent histogram time-to-digital converters is... Fixed; phase difference Multiply by the number of time-to-digital converters in a set of histograms , equal to the clock period of the reference clock .

[0106] In one embodiment, the histogram time-to-digital converter includes a measurement window control module. During each ranging cycle, after the Start signal, the measurement window control module opens a finite, configurable time window at regular intervals, capturing only valid Stop signals within this window. This embodiment effectively suppresses background noise and sensor dark counting, improving the signal-to-noise ratio and system anti-interference capability. Furthermore, this embodiment can also shield the signal within the first time unit of the first histogram time-to-digital converter, facilitating subsequent calculation of equivalent histogram data.

[0107] Please refer to Figure 9 In one embodiment, step S200 includes:

[0108] Step S210: Calculate the number of equivalent time units in the equivalent histogram data based on the number of histogram time-to-digital converters in the same histogram time-to-digital converter group and the number of time units in the histogram data.

[0109] Step S220: Calculate the equivalent clock period of the equivalent time unit in the equivalent histogram data based on the clock period of the reference clock and the number of histogram time-to-digital converters in the same histogram time-to-digital converter group.

[0110] Step S230: Calculate the equivalent photon count for each time unit in the equivalent histogram data based on the photon count for each time unit in each histogram data.

[0111] In one embodiment, step S210 uses the following calculation formula:

[0112]

[0113] in, The number of equivalent time units;

[0114] This represents the number of time units in the histogram data.

[0115] This represents the number of histogram time-to-digital converters in the same histogram time-to-digital converter group.

[0116] In one embodiment, step S220 uses the following calculation formula:

[0117]

[0118] in, The equivalent clock period for an equivalent time unit;

[0119] The clock period of the reference clock;

[0120] This represents the number of histogram time-to-digital converters in the same histogram time-to-digital converter group.

[0121] In one embodiment, step S230 uses the following calculation formula:

[0122] for :

[0123]

[0124] for ,

[0125]

[0126] for ,

[0127]

[0128] Where i is the sequence number of the equivalent time unit;

[0129] n is the number of histogram time-to-digital converters in the same histogram time-to-digital converter group;

[0130] It is a positive integer;

[0131] It is an integer, and ;

[0132] For the first Equivalent photon count for each equivalent time unit;

[0133] The first in the same histogram time-to-digital converter group The first histogram data of the time-to-digital converter Photon count per time unit;

[0134] The first in the same histogram time-to-digital converter group The first histogram data of the time-to-digital converter Photon count per time unit.

[0135] Please refer to Figure 10 In one embodiment, a set of histogram time-to-digital converters includes three histogram time-to-digital converters. Each time the timing control module sends a start signal and the timer begins operation, the input signal is shielded within the time range corresponding to the first time unit of the Histo-TDC1 to meet the computational processing requirements. After the required number of repeated measurements is met, the timing control module controls the data processing module to process the time unit register data of the three histogram time-to-digital converters, obtaining the equivalent histogram data corresponding to the three histogram time-to-digital converters. The data in the first three equivalent time units of the equivalent histogram data is equal to 0.

[0136] Please refer to Figure 11 In one embodiment, step S300 includes:

[0137] Step S310: Determine the time unit number of the echo signal based on the equivalent histogram data;

[0138] Step S320: Obtain the flight time of the laser pulse based on the time unit sequence number of the echo signal and the equivalent clock period.

[0139] In one embodiment, step S310 includes:

[0140] Step S311: Determine a time unit interval from the equivalent histogram data. The time unit interval includes the rising edge of the photon count value, the peak value of the photon count value, and the falling edge of the photon count value.

[0141] Step S312: Based on the photon count values ​​of each equivalent time unit within the time unit interval, perform a weighted average process on the sequence number of the equivalent time unit to obtain the weighted average time unit sequence number.

[0142] Step S313: Round down the weighted average time unit number to obtain the time unit number of the echo signal.

[0143] In one embodiment, in step S312, the weighted average time unit number is calculated using the following formula:

[0144]

[0145] in, The value of the calculated weighted average time unit number is also the centroid location. This is the equivalent time unit number. For the equivalent histogram data, the first The equivalent photon count corresponding to each equivalent time unit.

[0146] In one embodiment, step S320 includes:

[0147] The time of flight of the laser pulse is obtained by multiplying the time unit number of the echo signal by the equivalent clock period.

[0148] In one embodiment, after the weighted average processing (centroid algorithm processing) in step S312, the centroid position is obtained as 9.55. After the rounding processing in step S313, the time unit number of the obtained echo signal is 10.

[0149] The scope of protection of the ranging method in this application is not limited to the execution order of the steps listed in this embodiment. Any solution implemented by adding, subtracting, or replacing steps in the prior art based on the principles of this application is included within the scope of protection of this application.

[0150] In the embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, or methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative. For instance, the division of modules / units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules or units may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection of apparatuses or modules or units may be electrical, mechanical, or other forms.

[0151] The modules / units described as separate components may or may not be physically separate. The components shown as modules / units may or may not be physical modules; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules / units can be selected to achieve the objectives of the embodiments of this application, depending on actual needs. For example, the functional modules / units in the various embodiments of this application may be integrated into one processing module, or each module / unit may exist physically separately, or two or more modules / units may be integrated into one module / unit.

[0152] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0153] The descriptions of the processes or structures corresponding to the above figures each have their own emphasis. For parts of a process or structure that are not described in detail, please refer to the relevant descriptions of other processes or structures.

[0154] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this application should still be covered by the claims of this application.

Claims

1. A ranging method based on a lidar system, characterized in that, The lidar system includes: The timing control module is used to generate laser trigger signals and start timing signals; A laser emitting unit is used to respond to the laser trigger signal and emit laser pulses; The echo receiving unit is used to receive the echo signal and generate a stop timing signal; Clock source, used to generate a reference clock; A clock generation module is used to receive the reference clock and generate multiple reference clocks with the same frequency and a fixed phase difference. The histogram time-to-digital converter group includes multiple histogram time-to-digital converters, each of which is connected to a reference clock; each histogram time-to-digital converter is used to receive the start timing signal and the stop timing signal, and generate histogram data based on the time difference between the two. The ranging method includes: The lidar system is used to generate a set of histogram data; Generate equivalent histogram data based on the aforementioned set of histogram data; The flight time of the laser pulse is calculated based on the equivalent histogram data. The distance is calculated based on the flight time and speed of light of the laser pulse; The step of generating equivalent histogram data based on the set of histogram data includes: The number of equivalent time units in the equivalent histogram data is calculated based on the number of histogram time-to-digital converters in the same histogram time-to-digital converter group and the number of time units in the histogram data. The equivalent clock period of the equivalent time unit in the equivalent histogram data is calculated based on the clock period of the reference clock and the number of histogram time-to-digital converters in the same histogram time-to-digital converter group. Based on the photon counts of each time unit in each histogram data, calculate the equivalent photon counts of each equivalent time unit in the equivalent histogram data; The equivalent photon count for each time unit in the equivalent histogram data is calculated based on the photon count for each time unit in each histogram data using the following formula: for : ； for , ； for , ； Where i is the sequence number of the equivalent time unit; n is the number of histogram time-to-digital converters in the same histogram time-to-digital converter group; It is a positive integer; It is an integer, and ; For the first Equivalent photon count for each equivalent time unit; The first in the same histogram time-to-digital converter group The first histogram data of the time-to-digital converter Photon count per time unit; The first in the same histogram time-to-digital converter group The first histogram data of the time-to-digital converter Photon count per time unit.

2. The ranging method based on a lidar system according to claim 1, characterized in that, The histogram time-to-digital converter includes: A counter is used to record the number of clock cycles between the start timing signal and the stop timing signal; Multiple time unit registers are provided, with one time unit register corresponding to each clock cycle number. When the counter receives the stop timing signal once, the value in the time unit register corresponding to the clock cycle number is incremented by one.

3. The ranging method based on a lidar system according to claim 1, characterized in that, The clock generation module is configured to: receive the reference clock, perform frequency multiplication on the reference clock to obtain a frequency multiplied clock, and delay the frequency multiplied clock to generate multiple reference clocks, each reference clock having the same frequency and a fixed phase difference.

4. The ranging method based on a lidar system according to claim 1, characterized in that, The clock generation module uses a phase-locked loop circuit or an FPGA delay chain.

5. The ranging method according to claim 1, characterized in that, The equivalent clock period of the equivalent time unit in the equivalent histogram data is calculated based on the clock period of the reference clock and the number of histogram time-to-digital converters in the same histogram time-to-digital converter group, using the following calculation formula: ； in, The equivalent clock period for an equivalent time unit; The clock period of the reference clock; This represents the number of histogram time-to-digital converters in the same histogram time-to-digital converter group.

6. The ranging method according to claim 1, characterized in that, The calculation of the laser pulse flight time based on the equivalent histogram data includes: The time unit number of the echo signal is determined based on the equivalent histogram data. The flight time of the laser pulse is obtained based on the time unit number of the echo signal and the equivalent clock period.

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