WO2021035697A1 - Time code demodulation processing circuit and method - Google Patents

Abstract

A time code demodulation processing circuit and method. The circuit comprises: a sampling circuit for sampling a photon event of a reflected light beam detected by a pixel unit so as to form a sampling signal; a histogram memory for storing a histogram to be drawn including a plurality of histogram time units; a time code sequence control memory for storing a correlation between pre-written sampling signals and histogram time units needing to be started; and a time code sequence controller for controlling, according to the correlation stored in the time code sequence control memory, the sampling signal to enter a corresponding histogram time unit for superposition so as to draw the histogram. The circuit allows an emitter to emit a pulse string with a pulse period far lower than the maximum flight time corresponding to the maximum measurement range, such that a frame rate can be improved to a great extent.

Description

Time code demodulation processing circuit and method Technical field

The present invention relates to the field of computer technology, in particular to a time code demodulation processing circuit and method for time code time flight distance measurement.

Background technique

The Time of Flight (TOF) method calculates the distance of an object by measuring the flight time of the beam in space. Because of its high accuracy and large measurement range, it is widely used in consumer electronics, unmanned aerial vehicles, AR/ VR and other fields.

Distance measurement systems based on the time-of-flight principle, such as time-of-flight depth cameras and lidars, often include a light source emitting end and a receiving end. The light source emits a beam to the target space to provide illumination, and the receiving end receives the beam reflected by the target. Calculate the distance of the object by calculating the time required for the beam to be reflected and received. When the direct time flight method is used for measurement, the transmitter emits a pulsed beam to the target. The pulsed beam is emitted at a certain frequency. The time interval between adjacent pulses (pulse period) must not be less than the maximum flight time corresponding to the maximum measurement distance of the system. In order to avoid the situation that the signal cannot be recognized. Therefore, the frame rate of the system is often limited by the maximum measurement distance. When the measurement distance of the system reaches 100 meters or more, the frame rate is very low, and it is difficult to meet the high frame rate requirements of some practical applications.

In addition, when multiple systems work synchronously in the same space, interference is prone to occur, that is, the receiving end of a certain system will not only receive the optical signal from its own transmitter, but also receive the optical signal emitted by the transmitter of other systems. , Thus causing errors.

The disclosure of the above background technical content is only used to assist the understanding of the inventive concept and technical solution of the present invention. It does not necessarily belong to the prior art of the patent application. There is no clear evidence that the above content has been published on the filing date of the patent application. Under the circumstances, the above-mentioned background technology should not be used to evaluate the novelty and inventiveness of this application.

Summary of the invention

In order to solve at least one of the limitation of the frame rate of the system by the maximum measurement distance and the problem of multi-machine interference, the present application provides a time code demodulation processing circuit and a demodulation processing method for time code time flight distance measurement.

A time code demodulation processing circuit, connected to the pixel unit, includes:

A sampling circuit configured to sample the photon events of the reflected light beam detected by the pixel unit to form a sampling signal;

A histogram memory, configured to store a histogram to be drawn containing multiple histogram time units;

A time code sequence control memory, configured to store the correspondence between the pre-written sampling signal and the histogram time unit that needs to be turned on;

The time code sequence controller is configured to control the corresponding relationship stored in the memory according to the time code sequence to control the sampling signal to enter the corresponding histogram time unit for superimposition to draw the histogram.

Further, the processing circuit is configured to determine the time corresponding to the pulse waveform in the histogram; and determine the flight time according to the time corresponding to the pulse waveform.

Further, the time code is a regular time code [Δt, 2Δt, 3Δt,..., (n-1)Δt], where Δt is the pulse period, and n is the number of pulses included in the pulse train.

Further, the time code is a random time code [Δt ₁ , Δt ₁ + Δt ₂ , Δt ₁ + Δt ₂ + Δt ₃ ,..., Δt ₁ + Δt ₂ …+Δt _(n-1) ], Δt _i represents The time interval between the ith pulse and the (i+1)th pulse, i=1, 2,...(n-1), where n is the number of pulses contained in the pulse train.

Further, the time code is a double random time code, including a first random time code [Δt ₁ , Δt ₁ + Δt ₂ , Δt ₁ + Δt ₂ + Δt ₃ ,..., Δt ₁ + Δt ₂ …+Δt _{(n -1)} ] and the second random time code [ΔT ₁ , ΔT ₁ +ΔT ₂ , ΔT ₁ +ΔT ₂ +ΔT ₃ ,..., ΔT ₁ +ΔT ₂ …+ΔT _(N-1) ], where Δt _i represents The time interval between the i-th pulse and the (i+1)-th pulse in the pulse group, i=1, 2,...(n-1), n is the number of pulses in the pulse group; ΔT _j represents the j-th pulse The time interval between the pulse group and the (j+1)th pulse group, j=1, 2,...(N-1), and N represents the number of the pulse group.

A time code demodulation processing method, including the following steps:

Pre-write the corresponding relationship between the sampling signal and the histogram time unit in the histogram memory that needs to be turned on into the time code sequence control memory;

Sampling the photon events of the reflected light beam detected by the pixel unit by the sampling circuit to form the sampling signal;

The time code sequence controller controls the corresponding relationship stored in the memory according to the time code sequence to control the sampling signal to enter the histogram time unit in the histogram memory for superimposition to draw a histogram.

Further, the method further includes the following steps:

Determining the time corresponding to the pulse waveform in the histogram;

The flight time is determined according to the time corresponding to the pulse waveform.

Further, the time code is a regular time code [Δt, 2Δt, 3Δt,..., (n-1)Δt], where Δt is the pulse period, and n is the number of pulses included in the pulse train.

Further, the time code is a random time code [Δt ₁ , Δt ₁ + Δt ₂ , Δt ₁ + Δt ₂ + Δt ₃ ,..., Δt ₁ + Δt ₂ …+Δt _(n-1) ], Δt _i represents The time interval between the ith pulse and the (i+1)th pulse, i=1, 2,...(n-1), where n is the number of pulses contained in the pulse train.

Further, the time code is a double random time code, including a first random time code [Δt ₁ , Δt ₁ + Δt ₂ , Δt ₁ + Δt ₂ + Δt ₃ ,..., Δt ₁ + Δt ₂ …+Δt _{(n -1)} ] and the second random time code [ΔT ₁ , ΔT ₁ +ΔT ₂ , ΔT ₁ +ΔT ₂ +ΔT ₃ ,..., ΔT ₁ +ΔT ₂ …+ΔT _(N-1) ], where Δt _i represents The time interval between the i-th pulse and the (i+1)-th pulse in the pulse group, i=1, 2,...(n-1), n is the number of pulses in the pulse group; ΔT _j represents the j-th pulse The time interval between the pulse group and the (j+1)th pulse group, j=1, 2,...(N-1), and N represents the number of the pulse group.

The beneficial effects of the present invention:

The present invention provides a time code demodulation processing circuit and a demodulation processing method for time code time flight distance measurement. The present invention can allow a transmitter to transmit pulses with a pulse period that is much lower than the maximum measurement range corresponding to the maximum flight time. String, which can greatly increase the frame rate. Further, a preferred embodiment of the present invention also provides a time code demodulation processing circuit and a demodulation processing method, which are used to implement anti-interference time code time flight distance measurement.

Description of the drawings

Fig. 1 is a schematic diagram of a time-of-flight distance measurement system according to an embodiment of the present invention.

Fig. 2(a) is a schematic diagram showing that the corresponding time code is a regular time code according to an embodiment of the present invention, and the transmitter transmits a pulse train containing n pulses with a pulse period Δt.

Fig. 2(b) is a schematic diagram showing that the corresponding time code is a regular time code according to an embodiment of the present invention, and the collector successively receives the photons in the pulse train reflected by the target after time t.

Fig. 3(a) is a schematic diagram of a frame period single-photon counting sequence string of regular time encoding according to an embodiment of the present invention.

Fig. 3(b) is a histogram formed after superimposing regular time codes according to an embodiment of the present invention.

Fig. 4(a) is a schematic diagram of the corresponding time code being a random time code according to an embodiment of the present invention, and the transmitter transmits a pulse train containing n pulses in a random time interval.

Fig. 4(b) is a schematic diagram showing that the corresponding time code is a random time code according to an embodiment of the present invention, and the collector successively receives the photons in the pulse train reflected by the target after time t.

Fig. 5(a) is a schematic diagram of a frame period single photon counting sequence string of random time encoding according to an embodiment of the present invention.

Fig. 5(b) is a histogram formed after random time code superposition according to an embodiment of the present invention.

Fig. 6(a) is a schematic diagram showing that the corresponding time code is a double random time code according to an embodiment of the present invention, and the transmitter transmits N*n pulses in a double random time interval.

Fig. 6(b) is a schematic diagram showing that the corresponding time code is a double random time code according to an embodiment of the present invention, and the collector successively receives photons in the pulse train reflected by the target after time t.

Fig. 7(a) is a schematic diagram of a single-photon counting sequence of N pulse group periods with double random time coding according to an embodiment of the present invention.

Fig. 7(b) is a histogram formed after double random time coding is superimposed according to an embodiment of the present invention.

Fig. 8 is a schematic diagram of a time code demodulation processing circuit according to an embodiment of the present invention.

Fig. 9 is a schematic diagram of another time code demodulation processing circuit according to an embodiment of the present invention.

detailed description

In order to make the technical problems, technical solutions, and beneficial effects to be solved by the embodiments of the present invention clearer, the following further describes the present invention in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, but not to limit the present invention.

It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, the connection can be used for fixing or circuit connection.

It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top" The orientation or positional relationship indicated by "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying what is meant. The device or element must have a specific orientation, be configured and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first" and "second" may explicitly or implicitly include one or more of these features. In the description of the embodiments of the present invention, "plurality" means two or more, unless otherwise specifically defined.

Time-of-flight measurement system

The invention provides a time-flight distance measuring system, which has stronger anti-ambient light ability and higher resolution.

Fig. 1 is a schematic diagram of a time-of-flight distance measurement system according to an embodiment of the present invention. The distance measurement system 10 includes a transmitter 11, a collector 12, and a processing circuit 13. The transmitter 11 provides a emitted light beam 30 to the target space to illuminate an object 20 in the space. At least part of the emitted light beam 30 is reflected by the object 20 to form a reflected light beam. 40. At least part of the light signals (photons) of the reflected light beam 40 are collected by the collector 12. The processing circuit 13 is connected to the transmitter 11 and the collector 12 respectively, and the trigger signals of the transmitter 11 and the collector 12 are synchronized to calculate the light beam from the transmitter The time required for 11 to be emitted and received by the collector 12, that is, the flight time t between the emitted light beam 30 and the reflected light beam 40, further, the distance D of the corresponding point on the object can be calculated by the following formula:

D=c·t/2 (1)

Among them, c is the speed of light.

The transmitter 11 includes a light source 111 and an optical element 112. The light source 111 can be a light source such as a light emitting diode (LED), an edge emitting laser (EEL), a vertical cavity surface emitting laser (VCSEL), etc., or an array light source composed of multiple light sources. Preferably, the array light source 111 is a monolithic semiconductor A plurality of VCSEL light sources are generated on the substrate to form a VCSEL array light source chip. The light beam emitted by the light source 111 may be visible light, infrared light, ultraviolet light, or the like. The light source 111 emits light beams outward under the control of the processing circuit 13. For example, in one embodiment, the light source 111 emits a pulsed light beam at a certain frequency (pulse period) under the control of the processing circuit 13, which can be used in the direct time flight method ( In Direct TOF measurement, the frequency is set according to the measurement distance, for example, it can be set to 1MHz～100MHz, and the measurement distance is from several meters to several hundred meters. It is understandable that it may be a part of the processing circuit 13 or a sub-circuit independent of the processing circuit 13 to control the light source 111 to emit related light beams, such as a pulse signal generator.

The optical element 112 receives the pulsed beam from the light source 111, and optically modulates the pulsed beam, such as diffraction, refraction, reflection, etc., and then emits the modulated beam into space, such as a focused beam, a flood beam, and a structured light beam. Wait. The optical element 112 may be a lens, a diffractive optical element, a mask, a mirror, etc., or may be a MEMS galvanometer.

The processing circuit 13 can be an independent dedicated circuit, such as a dedicated SOC chip, FPGA chip, ASIC chip, etc., or a general-purpose processor. For example, when the depth camera is integrated into smart terminals such as mobile phones, TVs, and computers, The processor in the terminal can be used as at least a part of the processing circuit 13.

The collector 12 includes a pixel unit 121 and an imaging lens unit 122. The imaging lens unit 122 receives and guides at least part of the modulated light beam reflected by the object to the pixel unit 121. In an embodiment, the pixel unit 121 is composed of a single photon avalanche photodiode (SPAD), or an array pixel unit composed of multiple SPAD pixels. The array size of the array pixel unit represents the resolution of the depth camera, such as 320x240 Wait. SPAD can respond to the incident single photon to realize the detection of single photon. Because of its high sensitivity and fast response speed, it can realize long-distance and high-precision measurement. Compared with CCD/CMOS and other image sensors based on the principle of light integration, SPAD can count single photons, such as the use of time-correlated single photon counting (TCSPC) to realize the collection of weak light signals and the calculation of flight time . Generally, connected to the pixel unit 121 also includes a readout circuit composed of one or more of a signal amplifier, a time-to-digital converter (TDC), an analog-to-digital converter (ADC) and other devices (not shown in the figure). ). These circuits can be integrated with the pixels, and they can also be part of the processing circuit 13. For ease of description, the processing circuit 13 will be collectively regarded.

In some embodiments, the distance measurement system 10 may also include a color camera, an infrared camera, an IMU, and other devices. The combination of these devices can achieve richer functions, such as 3D texture modeling, infrared face recognition, SLAM and other functions.

In some embodiments, the transmitter 11 and the collector 12 can also be arranged in a coaxial form, that is, the two are realized by optical devices with reflection and transmission functions, such as a half mirror.

In the direct time-of-flight distance measurement system using SPAD, a single photon incident on the SPAD pixel will cause an avalanche, the SPAD will output an avalanche signal to the TDC circuit, and then the TDC circuit will detect the time interval between the photon emission from the emitter 11 and the avalanche. After multiple detections, the time interval is passed through a time-correlated single photon counting (TCSPC) circuit for histogram statistics to recover the waveform of the entire pulse signal, so as to achieve accurate flight time detection, and finally calculate the distance information of the object according to the flight time. Assuming that the pulse period emitted by the pulse beam is Δt, the maximum measurement range of the distance measurement system is Dmax, and the corresponding maximum flight time is

Generally, Δt≥t ₁ is required to avoid signal aliasing, where c is the speed of light. If the number of times of multiple detections required by TCSPC is n, the time (frame period) to realize a single distance measurement will not be less than n*t ₁ . For example, the maximum measurement range is 150m, the corresponding pulse period Δt=1us, n=100000, then the frame period will not be less than 100ms, and the frame rate will be less than 10fps. It can be seen that the maximum measurement range in the TCSPC method limits the pulse period, which further affects the frame rate of distance measurement.

In order to solve this problem, according to the following embodiments, the system and method for time-coded time-of-flight measurement provided by the present invention can be implemented by several different time-coded pulse modulation and demodulation schemes, which are described in detail as follows.

Regular time coded pulse modulation and demodulation method

Figures 2(a) and 2(b) are schematic diagrams of time-coded pulse modulation according to an embodiment of the present invention. The transmitter 11 will be much smaller than the maximum flight time corresponding to the maximum measurement range Dmax

The pulse period Δt transmits a pulse train, and the pulse train contains n pulses, as shown in Figure 2(a). If the measured target is at D and the corresponding flight time is t, the collector 12 will successively receive the photons in the pulse train reflected by the target after the time t, as shown in Fig. 2(b). In order to avoid the mutual influence of pulse beams in two adjacent frame periods, the frame period T is set to T≥(n-1)·Δt+t ₁ , that is, when the target is at the maximum measurement distance, the last in the pulse train The time required for a pulse to be transmitted by the transmitter 11 until received by the collector 12 is exactly t ₁ , which ensures that all pulse trains in a single frame period will be received and there will be no adjacent frame periods The impact of the pulse within. In an embodiment, the maximum measurement range is also assumed to be Dmax=150m, n=100000, but the pulse period Δt=100ns, which is much smaller than the 1us in the previous embodiment, the frame period T≈10ms, and the frame rate is as high as 100fps.

It should be noted that the waveform of each pulse in the transmitted pulse train is often not as regular as the square wave shown in the figure, so the figure is only used as an example. The received pulse train is only an example, and what the collector 12 receives is actually a photon number sequence that can reflect the received pulse train, which will be described in detail later.

If you want to achieve such a high frame rate distance calculation, the traditional TCSPC method will no longer be applicable. For this purpose, the present invention provides a new time-coded continuous single-photon counting demodulation method.

Figures 3(a) and 3(b) are time-coded continuous single-photon counting demodulation methods according to an embodiment of the present invention. While the transmitter 11 emits a pulse train containing n pulses, the collector 12 will be activated to collect part of the photons in the pulse reflected from the target, and the processing circuit 13 will process and record the corresponding time of each incident photon, such as Use the TDC circuit to collect the incident photon time, and then use the processing circuit to identify and record the photon time, and finally form the frame period single photon counting time series as shown in Figure 3(a). Each square of the time series is It is the minimum time unit determined by the TDC time resolution. When a photon event is detected by the TDC within the time of the minimum time unit, it will be recorded (for example, the photon count value 1 in the figure means that the photon is detected in the minimum time unit) , The value in each square is the photon count value (0 or 1), and the total time length of the sequence string can be equal to the frame period. The time sequence string can be acquired by any appropriate method and stored in the memory, such as continuous acquisition by a TDC with a higher bandwidth, or acquisition by a TDC with a lower bandwidth through multiple acquisitions and splicing.

In one embodiment, the frame period single photon counting time series can also be collected by other types of circuits. For example, the sampling circuit can respond to the SPAD avalanche signal to directly obtain the time series. Therefore, the frame period single-photon counting sequence can also be referred to as the frame period single-photon sampling sequence.

In one embodiment, the collected frame period single photon counting time series is stored in the memory, and then the histogram circuit in the processor 13 draws the histogram based on the time series, which is similar to the traditional histogram drawing in TCSPC. The principle is different. The histogram in this embodiment will adopt a time-coded continuous single-photon count superposition method. In one embodiment, the minimum time unit (minimum storage unit bin) of the histogram is the same as the minimum time unit of the time series. For the time unit to be drawn, superimposition is performed according to the time code when the burst is transmitted, such as sequentially Overlay. The pulse train emits a total of n pulses with a pulse period Δt, and the corresponding time code is a regular time code, namely [Δt, 2Δt, 3Δt,..., (n-1)Δt]. The superposition based on the time code refers to the current The time unit to be drawn is the starting unit, and the photon counts in all time units that are separated from the starting unit by Δt, 2Δt, 3Δt,..., (n-1)Δt in the sequence string and the starting unit The photon count values are sequentially superimposed, and the superimposed photon count is used as the value of the time unit in the histogram. For example, for the superimposition of the first time unit of the histogram, as shown by the arrow in Figure 3(a). The histogram formed by time-coding and superimposing multiple time units is shown in Figure 3(b).

Depending on the distance of the target and the reflectivity of the target, only a few photons in each pulse may enter the collector 12 and generate an avalanche with a certain probability to cause a single photon counting event. From the statistical probability point of view, the collector 12 has the highest probability of collecting a photon counting event only when each pulse in the pulse train emitted by the transmitter 11 is reflected back to the collector 12 during the entire frame period. In other words, the probability of collecting photons at the moment of receiving the pulse train shown in Figure 2(b) is the highest, which means that the photon count value on the corresponding time unit in the time series in Figure 3(a) is The probability of "1" is significantly higher than other time units. Therefore, after the time-coded histogram is superimposed, there will be a peak at time t+(Δt, 2Δt, 3Δt,..., (n-1)Δt), that is, the number of collected photons is the largest, and because the superposition is successively superimposed , So the value of the time peak will gradually decrease in the future. But as long as the time of the first pulse peak is determined, the flight time t of the target can be calculated.

Generally, the time resolution of TDC is smaller than the pulse width, that is, the width of each time unit of the time series is smaller than the pulse width. After time-coded continuous single-photon counting is superimposed, the obtained histogram will show much Each time unit has a higher value and forms a waveform diagram reflecting the pulse shape. In this case, the time corresponding to the highest point of the waveform diagram can be used as the flight time to be measured.

It is understandable that when the frame period T>(n-1)·Δt+t ₁ , the photon acquisition time does not need to cover the entire frame period, but only needs to be within the time of [(n-1)·Δt+t ₁ ] Acquisition, that is, the length of the frame period single photon counting sequence string is [(n-1)·Δt+t ₁ ], and data processing can be performed during the rest of the frame period, such as histogram calculation, flight time calculation, and distance calculation Wait.

In one embodiment, when drawing the time-coded continuous single-photon count superimposed histogram, the size of the smallest time unit may be an integer multiple of each time unit in the frame period single-photon count sequence string, such as 2 times, thus Can reduce the amount of calculation and memory required for histogram drawing.

In one embodiment, when drawing the time-coded continuous single-photon count superimposition histogram, the interval between adjacent time units, that is, the step length, can be greater than 1, for example, time coding superimposition is performed every other time unit, which can also reduce The amount of calculation and memory required for drawing.

In one embodiment, the total time length of the histogram is [(n-1)·Δt+t ₁ ], _{when the time unit after time t 1 is} superimposed, there will be no more photon counts in the time unit in the time series. Values are superimposed, and the time unit involved in the superposition will gradually decrease. In fact, the preferred embodiment does not need to be drawn with the same frame cycle length histogram, but only needs to draw from zero to the period histogram of t _1, since only the target within the maximum measurement range, The first wave crest must appear, and the flight time t can be determined with the first wave crest.

In one embodiment, when searching for the pulse waveform in the histogram, it can be searched by setting a threshold value. Values above the threshold value are retained, and values below the threshold value are regarded as noise.

In one embodiment, the drawing order of the histogram can also be changed, that is, it is not necessary to start from 0 to draw time unit by time unit. For example, the dichotomy can be used to draw from the middle time. Once the first pulse waveform is found, continue drawing in the direction of the earlier time unit until no waveform is found in the earlier time period when the current pulse waveform is separated by Δt. At this time, it is considered that the time corresponding to the current pulse waveform is the flight time of the target. In short, any suitable search algorithm that can locate the first pulse waveform is suitable for this scheme. In this embodiment, the total time length of the histogram will be adaptively changed based on the execution process of the search algorithm. Once the first pulse waveform is drawn and detected, the calculation will stop, and then the first pulse waveform can be used for The wave crest position is determined to obtain the flight time t. Generally speaking, the total time length of the adaptively changed histogram will not exceed the maximum flight time t ₁ , so that the amount of calculation and memory consumption can be greatly reduced.

As shown in Figure 3(a) and Figure 3(b), using a new time-coding-based continuous single-photon counting demodulation method, compared with the traditional TCSPC, it has higher memory requirements and a relatively large amount of calculation. , But the benefits brought by it are also very obvious, that is, the transmitter 11 can be allowed to transmit pulse trains with a pulse period much lower than the maximum measurement range corresponding to the maximum flight time, so that the frame rate can be greatly improved. Nevertheless, the modulation and mediation methods shown in FIGS. 2(a) to 3(b) are still difficult to solve the problem of multi-machine interference. The present invention also provides a time-coded time-of-flight measurement method that can resist interference.

It is understandable that, in some embodiments, the process of drawing a frame period single-photon count time series string and drawing a histogram based on the time series string can also be combined into one, that is, the histogram can be drawn directly based on the photon count, or of course. Extend the two steps to more than three steps. The implementation principles are the same, but the implementation forms are different, and the corresponding hardware circuits will also be different. For example, the detailed description of the combination of two will be described in the specific processing circuit design later. The realization form of one can reduce the storage capacity. Therefore, any realization form that utilizes this principle falls within the protection scope of the present invention.

Random time coded pulse modulation and demodulation method

4(a) and 4(b) are schematic diagrams of random time-coded pulse modulation according to an embodiment of the present invention. Compared with the embodiment shown in Fig. 2(a) and Fig. 2(b), the pulses in this embodiment will be transmitted at preset random (pseudo-random) intervals, that is, the pulses are coded with random time [Δt ₁ , Δt ₁ +Δt ₂ ,Δt ₁ +Δt ₂ +Δt ₃ ,…,Δt ₁ +Δt ₂ …+Δt _(n-1) ], Δt _i represents the i-th pulse and the (i+1)th pulse The time interval of each pulse, i=1, 2,...(n-1), as shown in Figure 4(a). If the measured target is at D and the corresponding flight time is t, the collector 12 will successively receive the photons in the pulse train reflected by the target after the time t, as shown in Fig. 4(b). In order to avoid the mutual influence of pulse beams in two adjacent frame periods, the frame period T is set to

That is, when the most target is located at the maximum measurement distance, the time required for the last pulse in the pulse train from the beginning of reflection by the transmitter 11 to the end of being received by the collector 12 is exactly t ₁ , which ensures that it is in a single frame All the bursts in the period will be received and will not be affected by the pulses in the adjacent frame period. In an embodiment, the maximum measurement range is also assumed to be Dmax=150m, n=100000, if the average value of the random pulse period

It is much smaller than the 1 us in the previous embodiment, the frame period is T≈10 ms, and the frame rate is as high as 100 fps.

Figures 5(a) and 5(b) are random time coding continuous single photon counting demodulation methods according to an embodiment of the present invention. As in the embodiment shown in Figure 3(a) and Figure 3(b), while the transmitter 11 emits N pulse trains, the collector 12 will be activated to collect some of the photons in the pulse reflected from the target, and the processing circuit 13 will process and record the corresponding time of each incident photon, and finally form the frame period single photon count time series as shown in Figure 5(a). The time series records the photon count value in each time unit, and the time series The total time length of the string is the frame period.

In one embodiment, the collected frame period single photon counting time series is stored in the memory, and then the histogram circuit in the processor 13 draws a histogram based on the time series, which is similar to Figure 3(a) and Figure 3. Similar to the embodiment shown in (b), the histogram in this embodiment will also adopt a time-coded continuous single-photon count superposition method. The difference is that the time code is a random time code. For the time unit to be drawn, it will be coded according to the time when the burst is transmitted [Δt ₁ , Δt ₁ + Δt ₂ , Δt ₁ + Δt ₂ + Δt ₃ ,... , Δt ₁ +Δt ₂ …+Δt _(n-1) ] to superimpose, for example, superimpose sequentially. The current time unit to be drawn will be the starting unit, and the subsequent sequence in the sequence will be separated from the starting unit by Δt ₁ , Δt ₁ + Δt ₂ , Δt ₁ + Δt ₂ + Δt ₃ ,..., Δt ₁ + Δt ₂ … The photon count value in all time units of +Δt _(n-1) is sequentially superimposed with the photon count value in the starting unit, and the superimposed photon count is used as the value of the time unit in the histogram. For example, for the superposition method of the first time unit of the histogram, as shown by the arrow in Figure 5(a). The histogram formed by time-coding and superimposing multiple time units is shown in Figure 5(b).

In one embodiment, when drawing a time-coded continuous single-photon count superimposed histogram, the size of the smallest time unit may be an integer multiple of the frame period single-photon count sequence string, such as 2 times, thereby reducing the histogram drawing The amount of calculation and memory required at the time.

In one embodiment, when drawing the time-coded continuous single-photon count superimposition histogram, the interval between adjacent time units, that is, the step length, can be greater than 1, for example, time coding superimposition is performed every other time unit, which can also reduce The amount of calculation and memory required for drawing.

In one embodiment, the total time length of the histogram is [(n-1)·Δt+t ₁ ], _{when the time unit after time t 1 is} superimposed, there will be no more photon counts in the time unit in the time series. Values are superimposed, and the time unit involved in the superposition will gradually decrease. In fact, the preferred embodiment does not need to be drawn with the same frame cycle length histogram, but only needs to draw from zero to the period histogram of t _1, since only the target within the maximum measurement range, The first wave crest must appear, and the flight time t can be determined with the first wave crest.

In one embodiment, when searching for the pulse waveform in the histogram, it can be searched by setting a threshold value. Values above the threshold value are retained, and values below the threshold value are regarded as noise.

In one embodiment, the drawing order of the histogram can also be changed, that is, it is not necessary to start from 0 to draw time unit by time unit. For example, the dichotomy can be used to draw from the intermediate time, so that the pulse waveform can be quickly found. In short, the use of any suitable search algorithm that can locate the pulse waveform is suitable for this solution. In this embodiment, the total time length of the histogram will be adaptively changed based on the execution process of the search algorithm. Once the pulse waveform is detected, the calculation will stop, and then the pulse waveform can be used to determine the peak position to obtain the flight time t . Since this embodiment uses random time coding, in the histogram after superimposition, only one or more histogram time units corresponding to the time t of the reflection of the first pulse in the pulse train will form a higher value. There will be no multiple pulse waveforms like in Figure 3(b). In other words, only the time t of the reflection of the first pulse is used as the starting unit, and each time unit of subsequent superposition corresponds to the time of the reflection of each pulse in the pulse train. At this time, the probability of collecting photons is the highest. And the starting unit is highly unique due to random time coding. Therefore, once the time of the pulse waveform (peak) is identified in the histogram, the flight time t of the target can be calculated. Generally speaking, the total time length of the adaptively changed histogram will not exceed the maximum flight time t ₁ , so that the amount of calculation and memory consumption can be greatly reduced.

Similarly, in some embodiments, the process of drawing a frame period single-photon count timing string and drawing a histogram based on the timing string can also be combined into one, that is, the histogram can be drawn directly based on the photon count, or of course the two The two steps are expanded into more than three steps. The implementation principles are the same, but the implementation forms are different, and the corresponding hardware circuits will also be different. For example, the detailed description will be combined into one in the specific processing circuit design later. The realization form of, can reduce the storage capacity, so any realization form that uses this principle is within the protection scope of the present invention.

Double random time code pulse modulation and demodulation method

6(a) and 6(b) are schematic diagrams of dual random time-coded pulse modulation according to an embodiment of the present invention. Compared with the embodiment shown in Fig. 4(a) and Fig. 4(b), the pulse train in this embodiment will be transmitted at a preset double random (pseudo-random) interval, that is, all transmitted pulses are divided into multiple pulses Group, each pulse group contains multiple pulses, the pulses in the pulse group are coded with the first random time [Δt ₁ , Δt ₁ + Δt ₂ , Δt ₁ + Δt ₂ + Δt ₃ ,..., Δt ₁ + Δt ₂ …+ Δt _(n-1) ], Δt _i represents the time interval between the i-th pulse and the (i+1)-th pulse in each group, i=1, 2,...(n-1), n is The number of pulses in a pulse group; the second random time code is used between groups [ΔT ₁ , ΔT ₁ + ΔT ₂ , ΔT ₁ + ΔT ₂ + ΔT ₃ ,..., ΔT ₁ + ΔT ₂ …+ΔT _{(N- 1)} Transmit in the form of ], ΔT _j represents the time interval between the jth pulse group and the (j+1)th pulse group, j=1, 2,...(N-1), N represents the number of pulse groups, As shown in Figure 6(a), a total of N*n pulses are emitted for a single measurement. If the measured target is at D and the corresponding flight time is t, the collector 12 will successively receive the photons in the pulse train reflected by the target after the time t, as shown in Fig. 6(b). In order to avoid the mutual influence of pulse beams in two adjacent frame periods, the frame period T is set to

That is, when the most target is located at the maximum measurement distance, the time required for the last pulse in the pulse train from the beginning of reflection by the transmitter 11 to the end of being received by the collector 12 is exactly t ₁ , which ensures that it is in a single frame All the bursts in the period will be received and will not be affected by the pulses in the adjacent frame period. In an embodiment, the maximum measurement range is also assumed to be Dmax=150m, n=1000, N=100, if the average value of the pulse period in the group

Periodic Mean Between Groups

It is much smaller than the 1 us in the previous embodiment, the frame period is T≈10 ms, and the frame rate is as high as 100 fps.

Fig. 7(a) and Fig. 7(b) are a double random time coding continuous single photon counting demodulation method according to an embodiment of the present invention. The difference from the embodiment shown in Fig. 5(a) and Fig. 5(b) is that while the transmitter 11 transmits N*n pulses, the collector 12 does not collect during the entire pulse train transmission time period. Instead, the collector 12 will be activated to collect part of the photons in the pulse reflected from the target only during the time that each pulse group is emitted (considering the photon return time difference, it can be appropriately greater than the time period of the pulse group), the processing circuit 13 The corresponding time of each incident photon incidence will be processed and recorded, and finally a single photon counting time series of N pulse group cycles as shown in Figure 7(a) will be formed, and each time unit of the time series will record the photon count value. , The total time length of the sequence string is the time period corresponding to the pulse group.

In one embodiment, the collected N pulse group period single photon counting time series are stored in the memory, and then the histogram circuit in the processor 13 draws a histogram based on the time series. When drawing the histogram, the method of superimposing and fusing the traditional TCSPC with the time code in the embodiment shown in Figs. 3 and 5 is actually used. That is to say, the drawing is performed in two steps (the two steps are not sequential, and can also be crossed). The first step is similar to the traditional TCSPC method, that is, the photon counting in the corresponding time unit between the N pulse group period single photon counting sequence series Superimpose, as shown by the upward plus arrow in Figure 7(a); in the second step, the total sequence obtained in the first step is coded according to the first time of pulse emission in the pulse group [Δt ₁ , Δt ₁ + Δt ₂ , Δt ₁ + Δt ₂ + Δt ₃ ,…, Δt ₁ + Δt ₂ …+Δt _(n-1) ] superimpose, that is, take the current time unit to be superimposed as the starting unit, and combine the subsequent ones in the sequence string with this The starting unit is separated by Δt ₁ , Δt ₁ +Δt ₂ , Δt ₁ +Δt ₂ +Δt ₃ ,..., Δt ₁ +Δt ₂ …+Δt _(n-1) The photon count value and the starting unit in all time units The photon count values in are sequentially superimposed, and the superimposed photon count is used as the value of the time unit in the histogram. For example, for the superposition method of the first time unit of the histogram, as shown by the horizontal plus sign in Figure 7(a). Finally, the histogram shown in Figure 7(b) will be obtained.

In some embodiments, time code superposition can also be performed first and then TCSPC, that is, the single photon counting sequence of each pulse group period is superimposed according to the first time code, as shown in the horizontal plus sign in Figure 7(a) As shown; and then superimpose the corresponding time units in the N superimposed time series, as shown by the arrow plus sign in Figure 7 (a). Finally, the histogram shown in Figure 7(b) will be obtained.

Similarly, the size of the minimum time unit of the histogram can be an integer multiple of the minimum time unit of the time series. In addition, the interval between two adjacent time units of the histogram can also be greater than 1, for example, time code superimposition is performed every other time unit, which can also reduce the amount of calculation and memory required for rendering.

Similarly, the time length of the histogram can be adjusted adaptively and does not need to be the same as the period length of the pulse group. Generally, only need to draw _{the histogram from 0 to t 1 in} the time period, because only when there is a target in the maximum measurement range, the first wave crest will definitely appear, and the first wave crest can be determined Flight time t is out.

In one embodiment, when searching for the pulse waveform in the histogram, it can be searched by setting a threshold value. Values above the threshold value are retained, and values below the threshold value are regarded as noise.

In one embodiment, the drawing order of the histogram can also be changed, that is, it is not necessary to start from 0 to draw time unit by time unit. For example, the dichotomy can be used to draw from the intermediate time, so that the pulse waveform can be quickly found. In short, the use of any suitable search algorithm that can locate the pulse waveform is suitable for this solution. In this embodiment, the total time length of the histogram will be adaptively changed based on the execution process of the search algorithm. Once the pulse waveform is detected, the calculation will stop, and then the pulse waveform can be used to determine the peak position to obtain the flight time t . Since this embodiment uses random time coding, in the histogram after superimposition, only one or more histogram time units corresponding to the time t of the reflection of the first pulse in the pulse train will form a higher value. There will be no multiple pulse waveforms like in Figure 3(b). In other words, only the time t of the reflection of the first pulse is used as the starting unit, and each time unit of subsequent superposition corresponds to the time of the reflection of each pulse in the pulse train. At this time, the probability of collecting photons is the highest. And the starting unit is highly unique due to random time coding. Therefore, once the time of the pulse waveform (peak) is identified in the histogram, the flight time t of the target can be calculated. Generally speaking, the total time length of the adaptively changed histogram will not exceed the maximum flight time t ₁ , so that the amount of calculation and memory consumption can be greatly reduced.

Compared with the random modulation and demodulation method shown in Figures 4(a), 4(b) and Figures 5(a), 5(b), Figures 6(a), 6(b) and 7(a), Since the dual random modulation and demodulation method shown in 7(b) does not collect photons in the entire frame period, it can not only effectively reduce ambient light noise, but also greatly reduce the entry of photons emitted by other devices when multiple devices coexist. This anti-multi-machine interference effect is better.

Time code demodulation processing circuit and processing method

In order to realize the time code demodulation in the above embodiment, the present invention also provides a time code demodulation processing circuit and processing method.

Fig. 8 is a time code demodulation processing circuit according to an embodiment of the present invention. The time code demodulation processing circuit 82 is connected to the pixel unit 81. The pixel unit 81 may be a SPAD pixel for detecting the photons of the reflected light beam. The processing circuit 82 detects The arrival of each photon event is processed to calculate the flight time of the photon back and forth.

The time code demodulation processing circuit 82 of this embodiment includes a sampling circuit 821, a timing string memory 822, a read address register 823, a time code sequence memory 824, an addition register 825, a histogram time unit counter (referred to as a bin counter) 826, and a histogram Figure memory 827.

After the pixel unit 81 collects the photon signal of the reflected light beam, it will output a photon detection event represented by the pulse signal. During a period of time, the sampling circuit 821 will sample the pulse signal under the control of the clock signal (for example, 1 GHz) sent by the clock generator. A single-photon counting timing string is formed in the frame period. It can be understood that the sampling circuit 821 may also include a TDC circuit as described above, as long as it can generate a single-photon counting timing sequence from a photon counting event. The sampling time interval of the sampling circuit 821 is generally not less than the pulse width, so as to avoid the situation that photons cannot be sampled at a time corresponding to a pulse width. In one embodiment, when the pixel unit 81 detects a photon, the sampling circuit 821 will output a digital signal 1. When no photon is detected, the sampling circuit 821 will output a digital signal 0. Therefore, within a period of time, the sampling circuit 821 will output a digital signal of 0. A sequence of 0 and 1 is output, and the sequence formed in one frame period is the single photon counting sequence of the frame period.

The frame period single photon counting time series sampled by the sampling circuit 821 will be sequentially stored in the time series memory 822 according to the memory unit address. Generally, the memory size of the time series memory 822 is different according to the sampling time, for example, when sampling The duration is 1000ns, the sampling interval is 1ns, and the corresponding memory is 1000bits.

The time code sequence memory 824 is used to store pre-written time code sequences, such as the regular time code sequence shown in FIG. 2(a) or the random time code sequence shown in FIG. 4(a).

The read address register 823 is used to store the address of the memory unit in the time series memory 822 that needs to be read out. Under the control of the clock signal, the time series memory 822 will read the data at the corresponding address according to the address in the read address register 823 to Addition register 825. Subsequently, the read address register 823 will automatically jump to the next address that needs to be read. For example, if the current address is x, it will automatically jump to the next address that needs to be read based on the time code sequence stored in the time code sequence memory 824. The address of: x+Δt _i , where Δt _i is the time interval sequence value stored in the time code sequence memory 824.

The addition register 825 is used to perform addition calculations, and add the data currently stored in it with the data in the corresponding storage unit transferred from the time sequence memory 822. When all the sequences in the time code sequence memory 824 have been read, the The addition register 825 completes the calculation of a histogram time unit bin, and then writes the value into the histogram memory 827 to draw the histogram.

The bin counter 826 is used to store the number of the currently drawn bin. When all the sequences in the time code sequence memory 824 are read, that is, after the current bin drawing is finished, pulses are sent to the bin counter 826 and the addition register 825, and the bin counter 826 The number is automatically +1 to start the drawing of the next bin, the value of this bin is written into the histogram memory 827, and the addition register 825 is cleared to 0 at the same time.

After the bins of the histogram are drawn, the processing circuit 82 may further calculate the flight time based on the histogram.

In the embodiment shown in FIG. 8, the sampling of the data and the drawing of the histogram are performed sequentially in time sequence, that is, the sampling of the frame period single photon counting time series is first saved in the time series memory 822, and then the time series is executed. Data processing to obtain histogram. In order to reduce the processing time and increase the frame rate, in one embodiment, a multi-timing string memory 822 may be used, for example, a dual timing string memory 822 is used, and when one frame of data is sampled, it is stored in the first timing string memory 822. Subsequently, when the histogram is drawn using the time series in the first time series memory 822, the sampling circuit 821 works synchronously, and saves the sampled time series in the second time series memory 822. In this reciprocation, when the histogram is drawn using the time series in the second time series memory 822, the sampling circuit 821 saves the sampled time series in the first time series memory 822. In this way, the sampling time can be greatly increased, and the frame rate can be increased.

In an embodiment, based on the processing circuit shown in FIG. 8, the present invention also provides a time code demodulation method, which includes the following steps:

Save the time code sequence in the time code sequence memory 824 in advance;

The sampling circuit 821 samples the photon events of the reflected light beam detected by the pixel unit 81 to form a frame period single photon counting time series and save it in the time series memory 822;

Save the address of the memory unit in the timing string memory 822 that currently needs to be read into the read address register 823, and the address will automatically jump to the next address that needs to be read according to the time code sequence;

According to the address in the read address register 823, read the data at the corresponding address from the timing string memory 822 to the addition register 825;

The addition register 825 executes the addition operation between the data currently saved and the data read out by the timing string memory 822, and transmits the operation result to the corresponding bin of the histogram memory 827 to draw a histogram;

The number of the previously drawn bin is stored in the bin counter 826, and the number is automatically increased by 1 when the current bin drawing is completed.

The embodiment shown in FIG. 8 has higher requirements on the memory. For the current technological trend of highly integrating SPAD photosensitive and data processing circuits into a single chip, if the processing circuit is monolithically integrated, the capacity of the on-chip memory will be higher. It is not conducive to mass production of chips. To solve this problem, the present invention provides a demodulation method for real-time histogram drawing.

Figure 9 is a real-time time code demodulation processing circuit according to an embodiment of the present invention. The time code demodulation processing circuit 92 is connected to the pixel unit 91. The pixel unit 91 may be a SPAD pixel for detecting photons of the reflected light beam. The processing circuit 92 Each detected photon event is processed to calculate the round-trip flight time of the photon.

Considering that when the bins of each time unit of the histogram are superimposed, under the premise that the time code is determined, the time unit (that is, the time point of the corresponding photon event) in the sequence string required for each bin to perform the superposition calculation is based on time The code is known. Based on this, the corresponding relationship between each bin address and the time unit address in the time sequence that needs to be superimposed can be saved in advance. The photon count value output by the sampling circuit 921 in real time will be based on the corresponding relationship, and the current The bin corresponding to the photon count value, and then the photon count value is gated to enter the corresponding bin for superposition.

The time code demodulation processing circuit 92 of this embodiment includes a sampling circuit 921, a time code sequence controller 922, a time code sequence control memory 923, and a histogram memory 924.

After the pixel unit 91 collects the photon signal of the reflected light beam, it will output a photon detection event represented by the pulse signal. The sampling circuit 921 samples the pulse signal under the control of the clock signal (for example, 1 GHz) sent by the clock generator to output the sampling signal ( That is, the photon count value is 0 or 1), the sampling signal is sent to the time code sequence controller 922, and the time code sequence controller 922 will control the corresponding relationship stored in the memory 923 according to the time code sequence to control the sampling signal to enter the histogram memory 924 For example, the sampling signal can be selected by means of three-state gates, transmission gates, etc. to superimpose in the corresponding bins. The time code sequence control memory 923 saves the corresponding relationship between the sampling signal and the bin that needs to be turned on. For example, it contains a storage space of n x j, where n is the number of time bins, and j is the number of bins in the pixel unit. The number of bits of the measurement sequence is the same. For each clock function, the corresponding n bits of data are transmitted to the time code sequence controller 922 to control the gating of the corresponding sampling signal.

In an embodiment, based on the time code demodulation processing circuit shown in FIG. 9, the present invention also provides a time code demodulation method, which includes the following steps:

Pre-write the corresponding relationship between the sampling signal and the bin in the histogram memory 924 that needs to be turned on into the time code sequence control memory 923;

Sampling the photon events of the reflected light beam detected by the pixel unit 921 by the sampling circuit to form the sampling signal;

The time code sequence controller 922 controls the corresponding relationship stored in the memory 923 according to the time code sequence to control the sampling signal to enter the corresponding bin in the histogram memory 924 for superimposition to draw a histogram.

It is understandable that the processing circuits shown in Figs. 8 and 9 are not only applicable to the demodulation methods in the embodiments shown in Figs. 3(a), 3(b) and 5(a), 5(b), but are also applicable The demodulation method in the embodiment shown in Figs. 7(a) and 7(b).

It is understandable that in the above description, in order to facilitate the elaboration of the relationship between the various parts, each module is described independently. In practical applications, multiple modules can also be combined, such as timing string memory, time code memory, etc. It is the same memory. Therefore, equivalent alternatives through merging, splitting, etc. should also be regarded as the protection scope of the present invention.

It can be understood that when the distance ranging system of the present invention is embedded in a device or hardware, corresponding structural or component changes will be made to adapt to requirements. The essence of the distance ranging system of the present invention is still adopted, so it should be regarded as the present invention The scope of protection. The above content is a further detailed description of the present invention in combination with specific/preferred embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, they can also make several substitutions or modifications to the described embodiments, and these substitutions or modifications should be regarded as It belongs to the protection scope of the present invention. In the description of this specification, reference to the description of the terms "one embodiment", "some embodiments", "preferred embodiment", "examples", "specific examples", or "some examples" etc. means to incorporate the implementation The specific features, structures, materials or characteristics described in the examples or examples are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples and the features of the different embodiments or examples described in this specification without contradicting each other. Although the embodiments of the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope defined by the appended claims. In addition, the scope of the present invention is not intended to be limited to specific embodiments of the processes, machines, manufacturing, material composition, means, methods, and steps described in the specification. A person of ordinary skill in the art will easily understand that the above-mentioned disclosures, processes, machines, processes, machines, processes that currently exist or will be developed later that perform substantially the same functions as the corresponding embodiments described herein or obtain substantially the same results as the embodiments described herein can be used. Manufacturing, material composition, means, method, or step. Therefore, the appended claims intend to include these processes, machines, manufacturing, material compositions, means, methods, or steps within their scope.

Claims (10)

1. A time code demodulation processing circuit, connected to a pixel unit, characterized in that it comprises:

   A sampling circuit configured to sample the photon events of the reflected light beam detected by the pixel unit to form a sampling signal;

   A histogram memory, configured to store a histogram to be drawn containing multiple histogram time units;

   A time code sequence control memory, configured to store the correspondence between the pre-written sampling signal and the histogram time unit that needs to be turned on;

   The time code sequence controller is configured to control the corresponding relationship stored in the memory according to the time code sequence to control the sampling signal to enter the corresponding histogram time unit for superimposition to draw the histogram.
2. The time code demodulation processing circuit of claim 1, wherein the processing circuit is configured to determine the time corresponding to the pulse waveform in the histogram; and determine the flight time according to the time corresponding to the pulse waveform .
3. The time code demodulation processing circuit according to claim 1, wherein the time code is a regular time code [Δt, 2Δt, 3Δt,..., (n-1)Δt], where Δt is a pulse period, n Is the number of pulses contained in the pulse train.
4. The time code demodulation processing circuit according to claim 1, wherein the time code is a random time code [Δt ₁ , Δt ₁ + Δt ₂ , Δt ₁ + Δt ₂ + Δt ₃ ,..., Δt ₁ + Δt ₂ …+Δt _(n-1) ], Δt _i represents the time interval between the i-th pulse and the (i+1)th pulse, i=1,2,...(n-1), where n is the pulse train The number of pulses included.
5. The time code demodulation processing circuit according to claim 1, wherein the time code is a double random time code, including a first random time code [Δt ₁ , Δt ₁ + Δt ₂ , Δt ₁ + Δt ₂ + Δt ₃ ,…,Δt ₁ +Δt ₂ …+Δt _(n-1) ] and the second random time code [ΔT ₁ , ΔT ₁ +ΔT ₂ , ΔT ₁ +ΔT ₂ +ΔT ₃ ,…, ΔT ₁ +ΔT ₂ …+ΔT _(N-1) ], where Δt _i represents the time interval between the i-th pulse and the (i+1)-th pulse in the pulse group, i=1, 2,…(n-1), n is The number of pulses in the pulse group; ΔT _j represents the time interval between the jth pulse group and the (j+1)th pulse group, j=1,2,...(N-1), N represents The number of pulse groups.
6. A time code demodulation method, characterized in that it comprises the following steps:

   Pre-write the corresponding relationship between the sampling signal and the histogram time unit in the histogram memory that needs to be turned on into the time code sequence control memory;

   Sampling the photon events of the reflected light beam detected by the pixel unit by the sampling circuit to form the sampling signal;

   The time code sequence controller controls the corresponding relationship stored in the memory according to the time code sequence to control the sampling signal to enter the histogram time unit in the histogram memory for superimposition to draw a histogram.
7. 8. The time code demodulation processing method of claim 6, further comprising the following steps:

   Determining the time corresponding to the pulse waveform in the histogram;

   The flight time is determined according to the time corresponding to the pulse waveform.
8. The time code demodulation processing method according to claim 6, wherein the time code is a regular time code [Δt, 2Δt, 3Δt,..., (n-1)Δt], where Δt is the pulse period, n Is the number of pulses contained in the pulse train.
9. The time code demodulation processing method according to claim 6, wherein the time code is a random time code [Δt ₁ , Δt ₁ + Δt ₂ , Δt ₁ + Δt ₂ + Δt ₃ ,..., Δt ₁ + Δt ₂ …+Δt _(n-1) ], Δt _i represents the time interval between the i-th pulse and the (i+1)th pulse, i=1,2,...(n-1), where n is the pulse train The number of pulses included.
10. The time code demodulation processing method according to claim 6, wherein the time code is a double random time code, including a first random time code [Δt ₁ , Δt ₁ + Δt ₂ , Δt ₁ + Δt ₂ + Δt ₃ ,…,Δt ₁ +Δt ₂ …+Δt _(n-1) ] and the second random time code [ΔT ₁ , ΔT ₁ +ΔT ₂ , ΔT ₁ +ΔT ₂ +ΔT ₃ ,…, ΔT ₁ +ΔT ₂ …+ΔT _(N-1) ], where Δt _i represents the time interval between the i-th pulse and the (i+1)-th pulse in the pulse group, i=1, 2,…(n-1), n is The number of pulses in the pulse group; ΔT _j represents the time interval between the jth pulse group and the (j+1)th pulse group, j=1,2,...(N-1), N represents The number of pulse groups.

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