Time-of-Flight (TOF) Sensing Device and Its Control Method

Abstract

The present invention provides a time-of-flight (TOF) sensing device and a control method therefor. The sensing device includes: a single-photon avalanche diode (SPAD) array, the SPAD array including N groups of SPAD pixels with different sensitivities, where N is a natural number greater than or equal to 2; a logic control circuit configured to be connected between the SPAD array and a readout circuit for controlling the gating or shutting off of the SPAD pixel groups according to the measured distance; and a readout circuit including a time-to-digital converter (TDC) and a static random-access memory (SRAM). Among them, the TDC is used to record the breakdown time information of the SPAD pixel groups, and the SRAM is used to store a histogram of the breakdown time information recorded by the TDC for the controller to call.

Description

Technical Field

[0001] The present invention relates to the field of 3D depth sensing, and in particular, to a sensing control device for a Time of Flight (TOF) sensor and a control method thereof. Background Art

[0002] With the development of lidar technology, the Time of flight (TOF) ranging method has received increasing attention. The TOF principle is to continuously emit light pulses to the object to be measured, and then use a sensor to receive the light reflected from the object to be measured, and obtain the distance of the object to be measured by detecting the flight time of the light pulse.

[0003] A TOF sensor is an active optical sensor, which at least includes two main parts: a transmitting device and a receiving device. The transmitting device emits short-pulse laser light, which irradiates the object to be measured, and part of the laser light is reflected and received by the receiving device.

[0004] When performing short-distance ranging, due to the strong reflected light, signal saturation may occur and ranging may not be possible, or a stacking effect may occur, causing the recorded signal (histogram) to be distorted and the ranging accuracy to decrease. Under strong background light, due to the influence of the background light, a Single Photon Avalanche Diode (SPAD) type detector may experience avalanche breakdown before the arrival of the real signal, and due to the limitation of the dead time, the SPAD cannot respond to the real signal, resulting in a limited maximum detection distance.

[0005] To solve the above technical problems, it is urgent to enhance the performance of the TOF 3D sensing device, so as to achieve accurate ranging in the ranging scenario with strong light intensity at short distances for the TOF 3D sensing device. Summary of the Invention

[0006] Technical Problems to be Solved

[0007] When performing short-distance ranging, due to the strong reflected light, the TOF sensor may experience signal saturation, resulting in inability to range, or a stacking effect may occur, causing the recorded signal to be distorted and the ranging accuracy to decrease.

[0008] Technical Solutions

[0009] To solve the above problems, the present invention provides a TOF sensing device with higher precision. By configuring multiple groups of pixel groups with different sensitivities in the SPAD array, each pixel in each group can independently control the turn-on time to cope with detections at different distances. In addition, by multiplexing the same multi-event time-to-digital converter for multiple groups of pixels and time-division multiplexing the corresponding TDC and SRAM resources, the resources of the TDC and SRAM are minimized, the efficiency of the device is improved, and the cost is reduced.

[0010] The present invention provides a time-of-flight (TOF) sensing device, comprising: an SPAD array, the SPAD array including N types of SPAD pixel groups with different sensitivities, where N is a natural number greater than or equal to 2; a logic control circuit configured to be connected between the SPAD array and a readout circuit for controlling the gating or shutting off of the SPAD pixel groups according to the measured distance; and a readout circuit, the readout circuit including a TDC and an SRAM, wherein the TDC is used to record the breakdown time information of the SPAD pixel groups, and the SRAM is used to store a histogram of the breakdown time information recorded by the TDC for the controller to call.

[0011] The present invention provides a time-of-flight (TOF) sensing device, wherein the SPAD pixel groups include SPAD pixel groups with high sensitivity, SPAD pixel groups with medium sensitivity, and SPAD pixel groups with low sensitivity.

[0012] The present invention provides a time-of-flight (TOF) sensing device, wherein the sensitivity of the SPAD pixel groups is determined by at least one of: different pixel sizes, different fill efficiencies, filters with different transmittances, and different overvoltage values.

[0013] The present invention provides a time-of-flight (TOF) sensing device, wherein the logic control circuit is configured to gate the SPAD pixel groups with low sensitivity within a first time period when the measured distance is less than a first threshold.

[0014] The present invention provides a time-of-flight (TOF) sensing device, wherein the logic control circuit is configured to gate the SPAD pixel groups with high sensitivity within a second time period when the measured distance is greater than a second threshold.

[0015] The present invention provides a time-of-flight (TOF) sensing device, wherein the logic control circuit is configured to gate the SPAD pixel groups with medium sensitivity within a third time period when the measured distance is greater than the first threshold and less than the second threshold.

[0016] The present invention provides a time-of-flight (TOF) sensing device, wherein the first time period, the second time period, and the third time period are dynamically adjusted according to the information of the previous frame.

[0017] The present invention provides a time-of-flight (TOF) sensing device, wherein N groups of SPAD pixels with different sensitivities in the SPAD array are configured to be arranged at intervals from each other, such that the pixels in the same pixel group are not adjacent to each other.

[0018] The present invention provides a time-of-flight (TOF) sensing device, wherein the logic control circuit is configured to control the gating or shutting off of the SPAD pixel groups to turn on the pixels at intervals.

[0019] The present invention provides a method for controlling a time-of-flight (TOF) sensing device. The sensing control device of the TOF sensor includes an SPAD array, a logic control circuit, and a readout circuit. The method includes: dividing the measured distance into N groups; gating and shutting off N groups of SPAD pixels with different sensitivities in the SPAD array according to the measured distance by the logic control circuit; and recording the breakdown time information of the gated SPAD pixel groups and storing a histogram of the breakdown time information by the readout circuit, wherein N is a natural number greater than or equal to 2.

[0020] The present invention provides a method for controlling a time-of-flight (TOF) sensing device, wherein gating and shutting off N groups of SPAD pixels with different sensitivities in the SPAD array according to the measured distance by the logic control circuit includes: when the measured distance is less than a first threshold, gating the SPAD pixel group with low sensitivity in a first time period.

[0021] The present invention provides a method for controlling a time-of-flight (TOF) sensing device, wherein gating and shutting off N groups of SPAD pixels with different sensitivities in the SPAD array according to the measured distance by the logic control circuit includes: when the measured distance is greater than a second threshold, gating the SPAD pixel group with high-low sensitivity in a second time period.

[0022] The present invention provides a method for controlling a time-of-flight (TOF) sensing device, wherein gating and shutting off N groups of SPAD pixels with different sensitivities in the SPAD array according to the measured distance by the logic control circuit includes: when the measured distance is greater than the first threshold and less than the second threshold, gating the SPAD pixel group with medium-high sensitivity in a third time period.

[0023] The present invention provides a method for controlling a time-of-flight (TOF) sensing device, wherein the first time period, the second time period, and the third time period are dynamically adjusted according to the information of the previous frame.

[0024] The present invention provides a method for controlling a time-of-flight (TOF) sensing device. Among them, the logical control circuit gates and shuts off N SPAD pixel groups with different sensitivities in the SPAD array according to the measured distance, including: controlling the gating or shutting off of the N SPAD pixel groups to turn on the pixels at intervals.

[0025] Advantageous Effects

[0026] Compared with the prior art, the present invention provides a sensing control method and device for a TOF sensor, having the following advantageous effects: the presence of low-sensitivity SPAD pixels avoids signal saturation and pile-up effects caused by too strong reflected light during short-distance ranging, effectively improving the ranging accuracy at short distances; high-sensitivity pixels are turned on for relatively long distances to reduce the interference of background light; the SPAD array is turned on in a time-sharing manner to reduce the dead time of the overall system; the pixels are turned on at intervals to effectively reduce the crosstalk between pixels. Description of the Drawings

[0027] Figure 1 is a schematic diagram of a TOF sensing device according to an embodiment of the present invention,

[0028] Figure 2 is a schematic diagram of a SPAD array according to an embodiment of the present invention, and

[0029] Figure 3 is a schematic diagram of the working timing of a SPAD array according to an embodiment of the present invention. Detailed Embodiments

[0030] Before proceeding with the following detailed description, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms "coupled," "connected," and their derivatives refer to any direct or indirect communication or connection between two or more elements, whether or not those elements are in physical contact with each other. The terms "transmit," "receive," and "communicate," and their derivatives, encompass both direct and indirect communication. The terms "comprise" and "include," and their derivatives, mean including but not limited to. The term "or" is inclusive, meaning and / or. The phrase "associated with," and its derivatives, means including, included within, interconnected, containing, contained within, connected or connected to, coupled or coupled to, communicating with, cooperating with, interlacing, juxtaposed, adjacent, bound or bound to, having, having an attribute, having a relationship or having a relationship with, and so on. The term "controller" refers to any device, system, or part thereof that controls at least one operation. Such a controller may be implemented in hardware, or in a combination of hardware and software and / or firmware. The functions associated with any particular controller may be centralized or distributed, whether local or remote. The phrase "at least one," when used in conjunction with a list of items, means that different combinations of one or more of the listed items may be used, and only one item from the list may be required. For example, "at least one of A, B, C" includes any one of the following combinations: A, B, C, A and B, A and C, B and C, A and B and C.

[0031] Definitions of other specific words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many cases, if not most cases, such definitions apply to the prior and future use of the words and phrases so defined.

[0032] In this patent document, the application combination of modules and the hierarchical division of sub-modules are only for illustration purposes. Without departing from the scope of the present disclosure, the application combination of modules and the hierarchical division of sub-modules can have different forms.

[0033] Figure 1 is a schematic diagram of a TOF sensing device according to an embodiment of the present invention.

[0034] Reference Figure 1 , the sensing control device of the time-of-flight (TOF) sensing device includes an SPAD array, a logic control circuit 140, a readout circuit, and a controller 130.

[0035] The SPAD array includes N groups of SPAD pixels with different sensitivities, where N is a natural number greater than or equal to 2. The SPAD array is capable of detecting the incidence of photons and outputting a pulse signal.

[0036] According to an embodiment of the present invention, the sensitivity can be determined by a) different pixel sizes or fill factors; b) filters with different transmittances; and c) different overvoltage levels.

[0037] According to an embodiment of the present invention, the SPAD pixel group includes one or a plurality of identical-sensitivity SPAD pixels connected in parallel.

[0038] The logic control circuit 140 is configured to be connected between the SPAD array and the readout circuit for controlling the gating or shutting off of the SPAD pixel group. Wherein, according to an embodiment of the present invention, each SPAD pixel group can control the SPAD gating / shutting-off time via an external enable signal through the logic control circuit 140. Specifically, the logic control circuit 140 can be configured to independently control N SPAD pixel groups. For example, the logic control circuit 140 can be configured to gate SPAD pixel groups with different sensitivities at different time periods according to the measured distance. According to an embodiment of the present invention, the logic control circuit 140 can be configured to only turn on the SPAD pixel groups with lower sensitivity at a relatively short distance to avoid the influence of event pile-up on the accuracy. In addition, the logic control circuit 140 can also be configured to only turn on the SPAD pixel groups with higher sensitivity at a relatively long distance to reduce the interference of background light. In addition, by time-divisionally turning on (enabling) the SPAD pixel groups in the SPAD array through the logic control circuit 140, the dead time of the overall system is reduced. In addition, the logic control circuit 140 can also be configured to time-divisionally turn on (enable) different SPAD pixel groups in the SPAD array to turn on the pixels at intervals, thereby effectively reducing the crosstalk between pixels.

[0039] The readout circuit includes a Time to Digital Convertor (TDC) 110 and a Static Random-Access Memory (SRAM) 120.

[0040] The TDC 110 is configured with a high-precision clock for recording the breakdown moment information of the SPAD pixels, that is, the moment when the SPAD array breaks down and generates a pulse signal.

[0041] The SRAM 120 stores the SPAD breakdown moment information recorded by the TDC 110 in the form of a histogram, for storing the histogram of the breakdown moment, that is, storing the photon information histogram of the SPAD breakdown moment information.

[0042] The controller 130 is configured to call and process data processing according to the histogram of the breakdown moment.

[0043] Figure 2 is a schematic diagram of the SPAD array according to an embodiment of the present invention.

[0044] refer to Figure 2 ,exist Figure 2 What is shown in FIG. 1 is a SPAD array when N=3, in which pixel groups with different sensitivities are configured to be arranged at intervals from each other so that pixels in the same pixel group are not adjacent to each other. Specifically, in the first row of the SPAD array, pixels in the second SPAD pixel group and the third SPAD pixel group are arranged at intervals starting with pixels in the second SPAD pixel group; and in the second row of the SPAD array, pixels in the third SPAD pixel group and the first SPAD pixel group are arranged at intervals starting with pixels in the third SPAD pixel group, and the arrangement of the first row and the second row is repeated to form a SPAD array. Figure 2 The array arrangement shown in , when different SPAD pixel groups in the SPAD array are turned on (turned on) by the logic control circuit 140 in a time-sharing manner, the pixels can be turned on at intervals to effectively reduce the crosstalk between pixels. Figure 2 The arrangement of the SPAD array when N=3 is shown in FIG. 3 , however, those skilled in the art should understand that the principles of the present invention can also be applied to SPAD arrays when N is other values, which does not deviate from the scope of the present invention.

[0045] Figure 3 Schematic diagram of the working timing of the SPAD array according to an embodiment of the present invention.

[0046] exist Figure 3 The working timing diagram when N=3 is shown in FIG. 1 , however, those skilled in the art should understand that the principle of the present invention can also be applied to SPAD arrays when N is other values, which does not deviate from the scope of the present invention.

[0047] refer to Figure 3 In the first time period T1, only the first SPAD pixel group with the lowest sensitivity is enabled; in the second time period T2, the second SPAD pixel group with the middle sensitivity is enabled, while the first SPAD pixel group continues to be turned on; in the third time period T3, all pixel groups including the third SPAD pixel group with the highest sensitivity are turned on. When the SPAD undergoes avalanche breakdown, a short pulse is generated and transmitted to the TDC via the logic control circuit, and the arrival time is recorded; the time recorded by the TDC is written into the SRAM. One frame of ranging is completed, and the above process is repeated to continue working.

[0048] According to the embodiment of the present invention, the first time period T1, the second time period T2, and the third time period T3 may be dynamically adjusted according to information of previous frames.

[0049] According to an embodiment of the present invention, a method for controlling a TOF sensing device is provided, including: dividing a measured distance into N groups, where N is a natural number greater than or equal to 2; gating and shutting off N SPAD pixel groups with different sensitivities in the SPAD array according to the measured distance by a logic control circuit; and recording the breakdown time information of the gated SPAD pixel groups and storing a histogram regarding the breakdown time by a readout circuit. After one frame of distance measurement is completed, the above process is repeated for continuous operation.

[0050] The method for controlling a TOF sensing device according to an embodiment of the present invention further includes: when the measured distance is less than a first threshold, gating the SPAD pixel group with low sensitivity in a first time period; when the measured distance is greater than a second threshold, gating the SPAD pixel group with high sensitivity in a second time period; and when the measured distance is greater than the first threshold and less than the second threshold, gating the SPAD pixel group with medium-high sensitivity in a third time period.

[0051] The method for controlling a TOF sensing device according to an embodiment of the present invention further includes: controlling the gating or shutting off of the N SPAD pixel groups to turn on the pixels at intervals.

[0052] Although the present disclosure has been described with exemplary embodiments, various changes and modifications can be suggested to those skilled in the art. The present disclosure is intended to cover such changes and modifications that fall within the scope of the appended claims.

[0053] Any description in the present invention should not be construed as implying that any particular element, step, or function is an essential element that must be included within the scope of the claims. The scope of the patent subject matter is defined only by the claims.

Claims

1. A time-of-flight (TOF) sensing device, comprising: A single-photon avalanche diode (SPAD) array, wherein the SPAD array includes N groups of SPAD pixels with different sensitivities, and N is a natural number greater than or equal to 2; A logic control circuit configured to be connected between the SPAD array and the readout circuit for controlling the gating or shutting off of the SPAD pixel groups according to the measured distance; A readout circuit, which includes a time-to-digital converter (TDC) and a static random access memory (SRAM). The TDC is used to record the breakdown time information of the SPAD pixel groups, and the SRAM is used to store a histogram of the breakdown time information recorded by the TDC for the controller to call. Among them, the SPAD pixel groups include SPAD pixel groups with high sensitivity, SPAD pixel groups with medium sensitivity, and SPAD pixel groups with low sensitivity, and Among them, the logic control circuit is configured to gate the SPAD pixel groups with low sensitivity within a first time period when the measured distance is less than a first threshold; to gate the SPAD pixel groups with low sensitivity and medium sensitivity within a second time period when the measured distance is greater than the first threshold and less than a second threshold; and to gate the SPAD pixel groups with low sensitivity, medium sensitivity, and high sensitivity within a third time period when the measured distance is greater than the second threshold. Among them, the N groups of SPAD pixels with different sensitivities in the SPAD array are configured to be arranged at intervals such that the pixels of the same pixel group are not adjacent to each other.

2. The time-of-flight (TOF) sensing device according to claim 1, wherein the sensitivity of the SPAD pixel groups is determined by at least one of: different pixel sizes, different fill factors, filters with different transmittances, and different overvoltage.

3. The time-of-flight (TOF) sensing device according to claim 1, wherein, The first time period, the second time period, and the third time period are dynamically adjusted according to the information of the previous frame.

4. The time-of-flight (TOF) sensing device according to claim 1, wherein, The logic control circuit is configured to control the gating or shutting off of the SPAD pixel groups to turn on the pixels at intervals.

5. A method for controlling a time-of-flight (TOF) sensing device, wherein the sensing control device of the TOF sensor includes a single-photon avalanche diode (SPAD) array, a logic control circuit, and a readout circuit. The method includes: Dividing the measured distance into N groups; Gating and shutting off N groups of SPAD pixels with different sensitivities in the SPAD array by the logic control circuit according to the measured distance; And Recording the breakdown time information of the gated SPAD pixel groups by the readout circuit and storing a histogram of the recorded breakdown time information, wherein N is a natural number greater than or equal to 2, wherein gating and shutting off N groups of SPAD pixels with different sensitivities in the SPAD array by the logic control circuit according to the measured distance includes: When the measured distance is less than the first threshold, a group of SPAD pixels with low sensitivity is gated within the first time period; when the measured distance is greater than the first threshold and less than the second threshold, a group of SPAD pixels with low sensitivity and medium sensitivity is gated within the second time period; and when the measured distance is greater than the second threshold, a group of SPAD pixels with low sensitivity, medium sensitivity, and high sensitivity is gated within the third time period. Among them, N groups of SPAD pixels with different sensitivities in the SPAD array are configured to be arranged at intervals from each other, so that the pixels of the same pixel group are not adjacent to each other.

6. The method according to claim 5, wherein The first time period, the second time period, and the third time period are dynamically adjusted according to the information of the previous frame.

7. The method according to claim 5, wherein, Gating and shutting off N groups of SPAD pixels with different sensitivities in the SPAD array according to the measured distance by the logic control circuit includes: controlling the gating or shutting off of the N groups of SPAD pixels to turn on the pixels at intervals.

Images