A multi-step DTOF ranging method based on dynamic resolution

Abstract

This invention discloses a multi-step DTOF ranging method based on dynamic resolution. It is a multi-step measurement method from initial target detection to high-precision target positioning, achieving the effect of a large number of histogram RAM bins required for traditional single-step ranging with fewer histogram RAM bins. While maintaining the counting accuracy of the time-to-digital converter (TDC), for a histogram RAM of depth N, two-step ranging can achieve N*N = N. 2 The ranging depth of bins; if three-step ranging is performed, then N*N*N = N 3 Distance depth measurement in bins; this is a method that trades 1 / N for k (k>=2) times the time cost. k‑1 This method requires significantly less histogram RAM resources, thus exponentially reducing the size of the required histogram RAM, resulting in substantial improvements in the area and power consumption of DTOF chips, especially large-area DTOF chips.

Description

Technical Field

[0001] This invention belongs to the field of integrated circuit technology, and in particular relates to a multi-step DTOF ranging method based on dynamic resolution. Background Technology

[0002] Semiconductor and single-photon avalanche diodes (SPADs) are single-photon avalanche diodes. With the advancement of SPAD technology, Time-to-Flight (DTOF) technology has a strong competitive advantage over other time-to-flight (TOF) technologies due to its high ranging accuracy over long distances and in complex background lighting environments, strong anti-interference capabilities, and fast dynamic response. However, because it uses time-correlated single-photon counting (TCSPC) technology, it needs to obtain target distance information through histogram statistical characteristics, which places a significant demand on the depth of histogram RAM bins. For example, if the ranging target range is 15m and the minimum accuracy of the ranging bin is 1.5cm, the required RAM depth is 15m / 0.015 = 1000 bins. Considering 12-bit peak counting, the corresponding RAM size is 12 x 1024 (assuming 2^34 bits for addressing). n (Integer), if a longer ranging range or higher ranging accuracy is required, the RAM will be correspondingly larger; this is especially serious in area arrays, which makes the area and power consumption of the RAM on the chip implementation the main limiting factors for chip cost and performance.

[0003] To address the aforementioned problems, this technical solution proposes a ranging method that reduces RAM bin requirements by adjusting resolution in multiple steps. This invention employs a k (k>=2)-step DTOF ranging method, and under flexible software control, achieves compression of the ranging histogram RAM, reaching 1 / N of the RAM size of conventional implementations. k-1 Size (N is the actual bin depth in the implementation), that is, the depth of N bins can achieve N k The equivalent effect of bins.

[0004] This multi-step ranging method is applicable to all cases where k>=2. For ease of description, we will only consider the case where k=2 in the following detailed description. Summary of the Invention

[0005] This invention provides a multi-step DTOF ranging method based on dynamic resolution, which solves the above problems.

[0006] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0007] A specific distance measurement process is achieved through two or more steps;

[0008] This technical solution uses a two-step ranging method as a specific example, with the following settings:

[0009] Let the number of bins in the histogram RAM be N, where N = 2. n =2 3 =8, and can be any other positive integer, without any range, but a larger n means a larger number of bins, a longer distance measurement, and more RAM (chip area, power consumption, etc.), which needs to be considered in the design; in this implementation, n is chosen as a positive integer 3;

[0010] The ranging range R bins, R = N * N = N 2 =2 2n =2 6 =64;

[0011] The TDC counter bit width K, K = 2n = 6; the counter bit width remains unchanged in all ranging steps, that is, the TDC accuracy remains unchanged.

[0012] The present invention provides a multi-step DTOF ranging method based on dynamic resolution, comprising the following steps:

[0013] S1. By progressively adjusting from coarse to fine resolution and gradually improving the positioning accuracy of the target: The ranging accuracy is adjusted to low by the distance accuracy controller, that is, the low n bits of the TDC counter are discarded, and only the high n bits cnt[2n-1:n] are sent to the histogram to cover the entire target ranging range, thereby obtaining the approximate range of the object to be measured. This distance value is used as the high n bits of the final ranging value; After digital signal analysis, let the final bin value of the object to be measured be N. msb ;

[0014] S2. By adjusting the distance accuracy controller, only the high-order bit information selected in the above steps is received, that is, only the value of the high n bits of TDC is N. msb Only then are the low n bits cnt[n-1:0] count values ​​sent to the histogram for statistics; the DSP analyzes this histogram statistics to obtain higher-precision position information of the object to be measured within the target range, and this position information is set as N. lsb , which are the lower n bits of the final ranging value;

[0015] S3. Combine the high and low n bits of data obtained in steps S1 and S2 to obtain the final 2n bits distance value {N}. msb N lsb}

[0016] Furthermore, the step-by-step adjustment in step S1 consists of at least two steps.

[0017] Furthermore, the resolution includes single pixels and array pixels.

[0018] The present invention has the following advantages over the prior art:

[0019] (1) The present invention is based on dynamic resolution adjustment, which decomposes the distance measurement process of the object to be measured into multiple steps from coarse to fine, thereby reducing the demand for histogram RAM.

[0020] (2) The present invention obtains a relatively coarse distance range of the object under test by using an initial relatively coarse accuracy; on this basis, the fine position of the object under test is gradually obtained by subsequent more precise positioning.

[0021] (3) Based on the technology of this invention, by using k-step ranging and k times the ranging time, N is obtained. k-1 Achieving a distance measurement accuracy multiple times, i.e., obtaining N bins of RAM depth. k The effect of bins;

[0022] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is an overall block diagram of a multi-channel implementation scheme that includes front-end transmitting, receiving, and digital processing modules;

[0025] Figure 2 This is a measurement schematic diagram of a two-step target measurement according to the present invention;

[0026] Figure 3 This is a flowchart illustrating the two-step method in its specific implementation. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The present invention provides a multi-step DTOF ranging method based on dynamic resolution, comprising the following steps:

[0029] S1. By progressively adjusting from coarse to fine resolution and gradually improving the positioning accuracy of the target: The ranging accuracy is adjusted to low by the distance accuracy controller DataCtlr, that is, the low n bits of the TDC counter are discarded, and only the high n bits cnt[2n-1:n] are sent to the histogram to cover the entire target ranging range, thereby obtaining the approximate range of the object to be measured. This distance value is used as the high n bits of the final ranging value; After digital signal analysis (DSP), let the final bin value of the object to be measured be N. msb ;

[0030] S2. By adjusting the distance accuracy controller DataCtlr, only the high-order bits selected in the above steps are received, that is, only the high n bits of TDC are N. msb Only then are the low n bits cnt[n-1:0] count values ​​sent to the histogram for statistics; the DSP analyzes this histogram statistics to obtain higher-precision position information of the object to be measured within the target range, and this position information is set as N. lsb , which are the low n bits of the final ranging value;

[0031] S3. Combine the high and low n bits of data obtained in steps S1 and S2 to obtain the final 2n bits distance value {N}. msb N lsb}

[0032] The step-by-step adjustment in step S1 consists of at least two steps.

[0033] Resolution includes single pixel and array pixel;

[0034] The specific implementation method is as follows:

[0035] like Figure 1 The diagram shows the basic principle and related module structure of this design. A Vertical-Cavity Surface-Emitting (VCSEL) laser, under the control of a controller, emits periodic laser pulses that illuminate the target object. Part of the laser is reflected back, triggering a single-photon avalanche diode (SPAD) trigger pulse at the receiver, thus obtaining the direct time-of-flight (DTOF) of the photons. This DTOF is then sent to a Time-to-Digital Converter (TDC) via an Analog Front-End (AFE) circuit to obtain the digitized delay. Based on the relationship between the speed of light (c) and the time difference (Δt), d = cΔt / 2, the distance d of the target object can be calculated. The DataController (DataCtlr) following the TDC selects different TDC counting fields for different ranging steps and inputs them into a statistical histogram (Historam). After digital signal processing (DSP), the final statistical result of the target position is obtained.

[0036] For a two-step ranging of an 8-bin histogram, the TDC count value is 6 bits, meaning the total number of count bins is 2. 2*3 =64 bins; In the first step of coarse resolution ranging, corresponding to 8 bins of the histogram, the lower 3 bits of the TDC count value are discarded under the control of DataCtlr, and only the higher 3 bits (i.e., coarse precision) are retained. Figure 2 As shown in -spep1, after histogram processing, the coarse distance value of the target object can be obtained, i.e., the high 3 bits are at the 3rd bin, that is, the coarse distance of the target R = 6'b011_xxx. The low 3 bits are to be measured in the next step.

[0037] Based on the high 3 bits of the target distance value, the DataCtlr controls the input histogram data. Only when the high 3 bits of data equal the target value from the previous step (i.e., a value of 3) is sent to the histogram for statistical analysis, thus obtaining a more precise target location, i.e., a low 3 bits of distance of 4. Figure 2 - As shown in step 2.

[0038] Through the above steps 1 and 2, a complete target distance value based on the two-step method is R = 6'011_100, which is 28. Thus, we obtained a 64-bin ranging distance using an 8-bin histogram RAM through the two-step method.

[0039] The digital signal processing module (DSP) is used for digital processing such as histogram filtering, peak search, and centroid interpolation.

[0040] Figure 3 The flowchart below illustrates the specific operation of this two-step ranging method. Considering the flexibility of software control, we implement it using embedded MCU firmware (FW). When a ranging command is received, the FW sets the current step flag to 1, configures the data controller (DataCtlr) to select the corresponding TDC counting bit, as described earlier, and then initiates hardware acquisition of the object's histogram. After DSP processing, the first-step ranging value is obtained. When the FW detects the end of the first-step ranging, it configures DataCtlr based on the obtained ranging value, sets the step flag to 2, and initiates the second-step hardware operation. When the high-order bit of the TDC count matches the result of step flag 1, DataCtlr sends the low-order bit of the count to the histogram, acquires the histogram data, processes it through the DSP, obtains the second-step ranging value, and combines the two-step ranging results to obtain a frame of high-precision target distance. To obtain the next frame, the above steps are repeated.

[0041] The above is a two-step implementation example, achieving the functionality of a 64-bin histogram RAM with only 8 bins of histogram RAM and the time cost of two distance measurements. Multi-step implementations are similar, obtaining the final distance measurement value sequentially from coarse to fine, and from high to low accuracy, thus completing the full distance measurement.

[0042] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A multi-step DTOF ranging method based on dynamic resolution, characterized in that, Includes the following steps: S1. By progressively adjusting from coarse to fine resolution and gradually improving the positioning accuracy of the target: The ranging accuracy is adjusted to low by the distance accuracy controller, that is, the low n bits of the TDC counter are discarded, and only the high n bits scnt[2n-1:n] are sent to the histogram to cover the entire target ranging range, thereby obtaining the approximate range of the object to be measured. This distance value is used as the high n bits of the final ranging value; After digital signal analysis, let the final bin value of the object to be measured be N. msb ; S2. By adjusting the distance accuracy controller, only the high-order bit information selected in the above steps is received, that is, only the value of the high n bits of TDC is N. msb Only then are the low n bits cnt[n-1:0] count values ​​sent to the histogram for statistics; The DSP analyzes the histogram statistics to obtain higher-precision position information of the object under test within the target range. This position information is set as N. lsb , which are the lower n bits of the final ranging value; S3. Combine the high and low n bits of data obtained in steps S1 and S2 to obtain the final 2n bits distance value {N}. msb N lsb }; The step-by-step adjustment in step S1 consists of at least two steps; The resolution includes single pixels and array pixels.

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