Detection circuit with adjustable output pulse width, receiving unit and laser radar

Abstract

The invention discloses a detection circuit with adjustable output pulse width, and the circuit comprises a single photon avalanche diode which can generate light current according to incident photons; the first input end of the comparator inputs an adjustable threshold signal, and the second input end of the comparator is coupled with the single photon avalanche diode so as to input an electric signal representing light current; the comparator is configured to output a waveform according to a comparison of the electrical signal and the adjustable threshold signal. The unit detection circuit provided by the invention has the following characteristics: when a plurality of photons are received by a single-photon avalanche diode in a short time, the pulse width of a circuit output signal is expanded, so that the information of the number of photons can be obtained through the signal pulse width, and the dynamic range of a single-photon avalanche diode device is expanded; in addition, the pulse width of the single-photon signal can be adjusted, in the range finding application, the pulse width of the single-photon signal can be configured to be close to the range finding light-emitting pulse width, a processing circuit can conveniently set a reasonable integral time window, and a better signal-to-noise ratio is obtained.

Description

Technical Field

[0001] The present invention generally relates to the field of optoelectronic technologies, and particularly to a detection circuit with adjustable output pulse width, a receiving unit including the detection circuit, a lidar, and a method for echo detection. Background Art

[0002] Currently, SPAD (Single Photon Avalanche Diode) units in lidar ranging applications can be divided into two categories: active quenching and passive quenching. Passive quenching SPAD units are as shown in Figure 1A . When a photon arrives, Figure 1A the diode 1 biased in Geiger mode in Figure 1B triggers an avalanche, generating Figure 1B the avalanche current 101 in Figure 2B the avalanche current 101 generates a voltage across the quenching resistor R ( Figure 2B the waveform 102 in Figure 2B ), and then the avalanche is quenched. The node 2 is discharged back to the ground potential by the quenching resistor R, and the diode 1 returns to the Geiger bias region. The waveform of node 2 becomes a digital pulse with a certain driving ability after passing through a buffer and is output to the subsequent processing circuit (the waveform 103 on the right in Figure 1). The buffer is usually composed of multiple inverters with a fixed switching threshold. The active quenching SPAD unit is shown in Figure 2. When a photon arrives ( Figure 2B the waveform 201 in

[0003] ), the diode 21 biased in Geiger mode triggers an avalanche. At this time, the NMOS transistor connecting the anode of the diode and GND is turned off (because the gate voltage 3 of the NMOS is 0V), and the NMOS is in a high-impedance state. The avalanche current generates a voltage at the drain of the NMOS transistor, and then the avalanche is quenched. The node 22 maintains a high level ( Figure 2B the waveform 202 in Figure 2B ), until after a delay of TDELAY (typical values are from a few ns to dozens of ns), the high level propagates to node 23 ( Figure 2B the waveform 203 in Figure 2B ), causing the NMOS to conduct, and node 22 is discharged to 0V, and the diode returns to the Geiger bias region. The pulse width of node 22 is approximately equal to the duration of TDELAY, and the waveform of node 22 becomes a digital pulse with a certain driving ability after passing through a buffer and is output to the subsequent processing circuit ( Figure 2B the waveform 204 in

[0003] ). The dotted part in the waveform 204 represents the dead time of the SPAD. During the time period corresponding to the dotted line, since the NMOS transistor continuously conducts and pulls node 22 to GND, the circuit is not in a normal working state waiting for photons to arrive. This period of time is regarded as the dead time until the NMOS transistor returns to the off state and the circuit returns to the working state.

[0003] In a passively quenched SPAD cell, the flip threshold of the buffer is fixed, so the width of the output pulse is fixed. When used in a lidar, device saturation is likely to occur under strong ambient light, resulting in abnormal ranging. In addition, since the output pulse width cannot be adjusted and cannot be adapted to the emission pulse width, in some cases of processing circuits, an optimized signal-to-noise ratio cannot be obtained, and the ranging performance deteriorates. In an actively quenched SPAD cell, the pulse width does not broaden with the photon sequence, thus losing the effective information required for ranging and judging the ambient light intensity. In addition, there is a dead time, causing signal distortion.

[0004] The content in the background art section is only the technology known to the applicant and does not necessarily represent the prior art in this field. Summary of the Invention

[0005] The present invention provides a detection circuit with adjustable output pulse width, a receiving unit applicable to a lidar, a lidar including the receiving unit, and a method for echo detection using the receiving unit.

[0006] The present invention provides a detection circuit with adjustable output pulse width, including:

[0007] A single-photon avalanche diode configured to generate a photocurrent according to incident photons; and

[0008] A comparator, with an adjustable threshold signal input to a first input terminal of the comparator, and a second input terminal of the comparator coupled to the single-photon avalanche diode to input an electrical signal representing the photocurrent; the comparator is configured to output a waveform according to a comparison result between the electrical signal and the adjustable threshold signal.

[0009] According to one aspect of the present invention, the cathode of the single-photon avalanche diode is coupled to a high voltage, the anode of the single-photon avalanche diode is grounded through a quenching resistor, and the anode is also coupled to the second input terminal of the comparator, where the electrical signal is an analog voltage output by the single-photon avalanche diode.

[0010] According to one aspect of the present invention, the cathode of the single-photon avalanche diode is coupled to a high voltage through a quenching resistor, the anode of the single-photon avalanche diode is grounded, and the cathode is also coupled to the second input terminal of the comparator through a capacitor, where the electrical signal is a change amount of the voltage of the cathode of the single-photon avalanche diode.

[0011] According to one aspect of the present invention, the detection circuit further includes a threshold control unit configured to output the adjustable threshold signal, and the threshold control unit is coupled to the first input terminal of the comparator to provide the adjustable threshold signal to the first input terminal.

[0012] According to one aspect of the present invention, the adjustable threshold signal increases as the intensity of the incident light increases.

[0013] The present invention also provides a receiving unit applicable to a lidar, comprising:

[0014] A detection circuit, the detection circuit comprising:

[0015] A single-photon avalanche diode configured to generate a photocurrent according to incident photons; and

[0016] A comparator, a first input end of the comparator inputs an adjustable threshold signal, a second input end of the comparator is coupled to the single-photon avalanche diode to input an electrical signal representing the photocurrent; the comparator is configured to output a waveform according to a comparison result between the electrical signal and the adjustable threshold signal; and

[0017] A processing unit coupled to an output end of the comparator of the detection circuit and configured to calculate the intensity of the incident light according to the waveform output by the comparator.

[0018] According to one aspect of the present invention, a cathode of the single-photon avalanche diode is coupled to a high voltage, an anode of the single-photon avalanche diode is grounded through a quenching resistor, and the anode is also coupled to the second input end of the comparator, wherein the electrical signal is a voltage across the quenching resistor.

[0019] According to one aspect of the present invention, the cathode of the single-photon avalanche diode is coupled to a high voltage through a quenching resistor, the anode of the single-photon avalanche diode is grounded, and the cathode is also coupled to the second input end of the comparator through a capacitor, wherein the electrical signal is a voltage of the single-photon avalanche diode.

[0020] According to one aspect of the present invention, the receiving unit further comprises a threshold control unit, the threshold control unit is coupled to the processing unit and configured to adjust the adjustable threshold signal according to the intensity of the incident light, and the threshold control unit is coupled to the first input end of the comparator to provide the adjustable threshold signal to the first input end.

[0021] According to one aspect of the present invention, the threshold control unit is configured to increase the adjustable threshold signal as the intensity of the incident light increases.

[0022] According to one aspect of the present invention, the receiving unit comprises a plurality of groups of the detection circuits and a summator, output ends of the comparators of the plurality of groups of detection circuits are coupled to an input end of the summator, and the summator performs a summation operation on outputs of the plurality of groups of detection circuits.

[0023] According to one aspect of the present invention, the adjustable threshold signal of the detection circuit is set such that: the width of the output waveform of the comparator of the detection circuit for a single photon matches the width of the laser pulse of the lidar.

[0024] According to one aspect of the present invention, the adjustable threshold signal of the detection circuit is set such that: the full width at half maximum of the output waveform of the comparator of the detection circuit for a single photon is equal to the full width at half maximum of the laser pulse of the lidar.

[0025] According to one aspect of the present invention, the processing unit is configured to calculate the number of incident photons according to the pulse width of the waveform output by the comparator.

[0026] The present invention also provides a lidar, comprising:

[0027] A transmitting unit, the transmitting unit includes a laser, and the laser is configured to emit a laser pulse to the outside of the lidar to detect a target;

[0028] The receiving unit as described above, the receiving unit is configured to receive the echo after the laser pulse is reflected on the target;

[0029] A calculation unit, the calculation unit is coupled to the receiving unit and is configured to calculate the distance and / or reflectivity of the target according to the waveform output by the comparator of the receiving unit.

[0030] The present invention also provides a method for detecting an echo using the receiving unit as described above.

[0031] The present invention also provides a laser detection method, comprising:

[0032] Emitting a detection laser beam for detecting a target;

[0033] Receiving the echo from the target through a single-photon avalanche diode, wherein the single-photon avalanche diode generates a photocurrent according to the incident photons;

[0034] Comparing, through a comparator, an electrical signal representing the photocurrent with an adjustable threshold signal to generate a digital signal output;

[0035] Adjusting the adjustable threshold signal according to the waveform of the digital signal output.

[0036] According to one aspect of the present invention, the step of adjusting the adjustable threshold signal according to the waveform of the digital signal output includes: increasing the adjustable threshold signal as the incident light intensity increases.

[0037] Embodiments of the present invention provide a single - photon avalanche diode unit circuit (pixel level circuit). This unit circuit has two characteristics: when multiple photons are received by the single - photon avalanche diode in a short time, the pulse width of the circuit output signal will broaden, so that information about the number of photons can be obtained through the signal pulse width, expanding the dynamic range of the single - photon avalanche diode device. The pulse width of the single - photon signal can be set and adjusted. In dTOF ranging applications, this characteristic can be used to configure the pulse width of the single - photon signal to be close to the width of the ranging light - emitting pulse, facilitating the processing circuit to set a reasonable "integration time window" and obtaining a better signal - to - noise ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings forming a part of this disclosure are used to provide a further understanding of the disclosure. The schematic embodiments and descriptions thereof of the disclosure are used to explain the disclosure and do not constitute an improper limitation of the disclosure. In the drawings:

[0039] Figure 1A and 1B respectively show a passively quenched single - photon avalanche diode detection circuit and its waveform;

[0040] Figure 2A and 2B respectively show an actively quenched single - photon avalanche diode detection circuit and its waveform;

[0041] Figure 3A shows a detection circuit according to an embodiment of the first aspect of the present invention;

[0042] Figure 3B shows Figure 3A a schematic diagram of the waveforms of each node in the detection circuit;

[0043] Figure 4 shows Figure 3A a schematic diagram of adjusting the pulse width by adjusting the threshold in the circuit;

[0044] Figure 5 shows a schematic diagram of increasing the dynamic range of the single - photon avalanche diode device by increasing the threshold when the ambient light is strong;

[0045] Figure 6A shows a detection circuit according to another embodiment of the first aspect of the present invention;

[0046] Figure 6B shows Figure 6A a schematic diagram of the waveforms of each node in the detection circuit;

[0047] Figure 7 shows a schematic diagram of a receiving unit that can be used in a lidar according to the second aspect of the present invention;

[0048] Figure 8 FIG. shows a schematic diagram of a receiving unit according to a preferred embodiment of the second aspect of the present invention;

[0049] Figure 9 shows Figure 8 a waveform schematic diagram of each node in the receiving unit of, for explaining the selection and optimization of the threshold;

[0050] Figure 10 FIG. shows a schematic diagram of a lidar according to the third aspect of the present invention; and

[0051] Figure 11 FIG. shows a schematic diagram of a laser detection method according to the fourth aspect of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0052] In the following, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the drawings and the description are considered to be exemplary in nature and not restrictive.

[0053] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed 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 quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0054] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "mounted", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection: it may be a mechanical connection, an electrical connection, or a connection capable of mutual communication; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0055] In the present invention, unless otherwise clearly specified or limited, the first feature being "on" or "under" the second feature may include the direct contact between the first and second features, or may include the contact between the first and second features through additional features therebetween rather than direct contact. Moreover, the first feature being "above", "over" and "on top of" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "beneath" and "underneath" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the horizontal height of the first feature is less than that of the second feature.

[0056] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numerals and / or reference letters in different examples. Such repetition is for the purpose of simplification and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those of ordinary skill in the art may be aware of the application of other processes and / or the use of other materials.

[0057] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0058] First aspect

[0059] Figure 3A A detection circuit 10 according to an embodiment of the first aspect of the present invention is shown, the output pulse width of which can be adjusted and broadened, so as to reflect the width of the emission pulse. The following will be described in detail with reference to Figure 3A Detailed description.

[0060] As Figure 3A shown, the detection circuit 10 includes a single-photon avalanche diode 11 and a comparator 12. The single-photon avalanche diode is a kind of optoelectronic detection avalanche diode with single-photon detection ability, which operates in Geiger mode, can generate photocurrent according to incident photons, and can be used for the detection of extremely weak optical signals. The first input terminal of the comparator 12 ( Figure 3AThe inverting input terminal (-) of the comparator 12 inputs an adjustable threshold signal Threshold, and the second input terminal (the non-inverting input terminal + of the comparator 12 in FIG. 3) is coupled to the single-photon avalanche diode 11 to input an electrical signal representing the photocurrent. The comparator 12 outputs a waveform according to the comparison result between the electrical signal and the adjustable threshold signal Threshold. For example, when the electrical signal is higher than the adjustable threshold signal Threshold, a high level is output; when the electrical signal is lower than the adjustable threshold signal Threshold, a low level is output. Vice versa.

[0061] As Figure 3A shown, according to a preferred embodiment of the present invention, the detection circuit 10 may further include a quenching resistor 13. The cathode of the single-photon avalanche diode 11 is coupled to a high voltage +HV, and the anode is grounded through the quenching resistor 13. In the Geiger mode, it can respond to the incident photon input excitation P. The anode of the single-photon avalanche diode 11 is also coupled to the second input terminal (non-inverting input terminal +) of the comparator 12, so as to provide the analog voltage output by the single-photon avalanche diode 11 to the comparator 12 as an electrical signal. Figure 3A The circuit structure shown is applicable to a P-on-N structure single-photon avalanche diode device because the anode of a single-photon avalanche diode of this structure does not need to be grounded. Therefore, it can be configured according to Figure 3A the circuit structure shown. The anode of an N-on-P structure single-photon avalanche diode usually needs to be grounded, and its specific circuit structure will be described in detail below. Single-photon avalanche diodes of both of these structures can be used in the expandable and adjustable detection circuit of the present invention.

[0062] Figure 3B shows Figure 3A in the circuit structure, when the single-photon avalanche diode 11 receives the photon input excitation P, the waveform A2 at the non-inverting input terminal of the comparator 12 and the waveform A3 at the output terminal of the comparator 12. When the photon input excitation P is a single photon, as Figure 3BAs shown by the single arrow in the photon input excitation P, the waveform A2 at the non-inverting input terminal of the comparator 12 corresponds to the signal waveform of a single photon, including a steeply rising front edge and an exponentially decaying trailing edge. The steeply rising front edge is due to the fact that the processes of avalanche and quenching occur very quickly, usually with a time < 1 ns, that is, the rise time of the front edge of the single photon signal < 1 ns. The exponentially decaying trailing edge corresponds to the recharge process of the single photon avalanche diode. After the avalanche is quenched by the quenching resistor, the high voltage power supply +HV charges the junction capacitance of the single photon avalanche diode through the quenching resistor 13 (with a resistance of RQ), and the charging time constant is RQxCD, thus forming an exponentially decaying trailing edge of the single photon signal. The typical value of the charging time constant ranges from a few ns to dozens of ns. Through the comparator 12, a digital waveform A3 is generated at the output terminal of the comparator 12. When the voltage of the waveform A2 is higher than the threshold Threshold, it corresponds to the high level of the waveform A3, and vice versa corresponds to the low level of the waveform A3.

[0063] When the photon input excitation P includes multiple consecutive photons, such as Figure 3B As shown by the three adjacent arrows in the photon input excitation P, the waveform A2 includes a corresponding number of single photon signal waveforms. Each single photon signal waveform includes a steeply rising front edge and an exponentially decaying trailing edge, as described above. And because the multiple consecutive photons are relatively close and the value of the threshold Threshold is low, lower than the valleys of the multiple consecutive single photon signal waveforms, the waveform A3 accordingly has a broadened output signal waveform.

[0064] Figure 4 The schematic diagram showing the pulse width adjustment by adjusting the threshold Threshold is shown. As Figure 4 shown, for the same photon input excitation P including one photon, when a lower threshold Threshold1 is adopted, the width of the waveform A3 obtained at the output terminal of the comparator 12 is significantly wider; when a higher threshold Threshold2 is adopted, the width of the waveform A3' obtained at the output terminal is significantly reduced. Therefore, by adjusting the threshold at which the comparator 12 flips, the time length during which the analog signal waveform output by the single photon avalanche diode 11 exceeds the threshold can be adjusted, thereby adjusting the width of the digital pulse output by the detection circuit 10 including the single photon avalanche diode.

[0065] The above pulse width adjustment function can achieve good application effects in many occasions. For example, when used in a lidar system, when the ambient light is strong (as Figure 5 shown, the incident photon excitation P includes multiple closely adjacent arrows), by increasing the threshold Threshold, the dynamic range of the single photon avalanche diode device can be increased, making it less likely to saturate. Specifically, as Figure 5As shown, when a lower threshold Threshold1 is adopted, in the case of strong ambient light, the single-photon avalanche diode device 11 is frequently triggered into avalanche by the incident ambient photons. As a result, before the single-photon avalanche diode 11 is fully charged after avalanche quenching, it is triggered into avalanche again. The waveform A3 at the output end of the comparator 12 is a waveform with a continuous high level. At this time, the detection circuit 10 cannot perform normal ranging measurements, nor can it accurately measure the ambient light intensity level. After adjusting to adopt a higher threshold Threshold2, the signal of the waveform A3' at the output end of the comparator 12 can change from a continuous high level to a random pulse output. At this time, although the ambient light noise is large, the single-photon avalanche diode device is not completely saturated and still has a certain ranging ability (usually, when the noise is large, multiple measurements are required to improve the signal-to-noise ratio to extract the effective signal), and it can evaluate the actual intensity of the ambient light through information such as the noise pulse width and frequency.

[0066] Those skilled in the art can easily understand that in the above embodiment, the comparator 12 adopts a voltage comparator, but the present invention is not limited thereto. The voltage comparator is only one embodiment, and a current comparator or other circuit structures with configurable flip thresholds (action thresholds) can also be adopted.

[0067] Based on the passive quenching SPAD unit, the above embodiment of the present invention adds a comparator with a configurable threshold. The comparator also acts as a buffer, and its output has a certain driving ability and can drive the subsequent processing circuit. This enables the output signal of the single-photon signal to have two characteristics: the width of the single-photon signal can be changed by adjusting the threshold; when a continuous photon sequence arrives, the output signal broadens along with the photon sequence. Those skilled in the art understand that the broadening of the output signal is beneficial to a certain extent and can be used to judge the intensity of the incident light or the ambient light. The specific degree of broadening can be determined according to the specific usage scenario and is not limited in the present invention.

[0068] Figure 6A Fig. 10 shows a detection circuit 10 according to another embodiment of the present invention. The circuit structure in Fig. 6 is applicable to a single-photon avalanche diode with an N-on-P structure because its anode usually needs to be grounded. As Figure 6AAs shown, the cathode of the single-photon avalanche diode 11 is coupled to the high voltage +HV through a quenching resistor 13, and the anode of the single-photon avalanche diode 11 is grounded, operating in Geiger mode. The cathode is also coupled to the second input terminal (the inverting input terminal in the figure) of the comparator 12 through a capacitor 14, so as to provide the change amount of the cathode voltage of the single-photon avalanche diode 11 to the inverting input terminal of the comparator 12 as the electrical signal. The capacitor 14 can block direct current and pass alternating current, so that only the change amount of the cathode voltage of the single-photon avalanche diode 11 can be provided to the inverting input terminal of the comparator 12. Similarly, the non-inverting input terminal of the comparator 12 is connected to the adjustable threshold Threshold. Figure 6B It shows Figure 6A During the operation of the detection circuit 10, according to the incident photon excitation P, the waveform A2 at the inverting input terminal of the comparator 12 and the waveform A3 at the output terminal of the comparator 12. Similar to that described above with reference to Figure 3A described, the difference is, for example, that in Figure 6A the circuit structure of, the change amount of the cathode voltage of the single-photon avalanche diode 11 (i.e., the waveform A2) is a downward sharp pulse. The specific working mode can be referred to the above description about Figure 3A , and will not be elaborated here.

[0069] Additionally preferably, the detection circuit 10 further includes a bias resistor R B , and the inverting input terminal of the comparator 12 is connected to the bias voltage V B through this bias resistor R BIAS , as Figure 6A shown.

[0070] Additionally, according to a preferred embodiment of the present invention, the detection circuit 10 further includes a threshold control unit, which is configured to generate and output the adjustable threshold signal according to the intensity of the ambient light. The threshold control unit is coupled to the first input terminal of the comparator to provide the adjustable threshold signal Threshold to the first input terminal. The following will be described with reference to Figure 7 . The threshold control unit can, for example, dynamically adjust the adjustable threshold signal, thereby changing the width of the single-photon signal in the output waveform A3 of the detection circuit, and can make the output signal widen as the continuous photon sequence arrives.

[0071] The detection circuit according to the first aspect of the present invention is described above. When a single-photon avalanche diode is triggered into avalanche by a photon, it will then go through a quenching and charging process and return to the normal operating state. For the detection circuit unit proposed in the embodiments of the present invention, if during the charging and recovery process, another photon or several other photons are incident on the photosensitive region of the single-photon avalanche diode and trigger an avalanche, it will cause the output signal of the detection circuit to broaden. The broadening rule is briefly described below. The total pulse width output by the detection circuit 10 is the total duration of the incident photon sequence plus the duration (pulse width) of the single-photon output pulse. For example, when the single-photon output pulse width is 5 ns, and 3 photons arrive continuously within a time length of 7 ns, then the total pulse width output by the detection circuit is 7 ns + 5 ns = 12 ns. A photon sequence in the sense of the present invention means that the maximum time interval between adjacent photons in a photon sequence needs to be less than a single-photon pulse width. If the time interval between two adjacent photons in a photon sequence exceeds a single-photon pulse width, then what is output is not a broadened pulse but two output pulses, and this photon sequence will be regarded as two photon sequences.

[0072] The broadening characteristic can play a quite significant role in the optoelectronic system. In the detection circuits of some single-photon avalanche diodes that do not have the broadening characteristic, within the time period after avalanche recovery (the typical value of the recovery time is several ns to dozens of ns), if other photons are incident on the photosensitive region of the single-photon avalanche diode, it will not cause any change in the output signal of the single-photon avalanche diode. It is equivalent to the recovery time of the single-photon avalanche diode being the "dead time" of the detection circuit. Therefore, for the detection circuit of a single-photon avalanche diode without the broadening characteristic, when the echo signal is strong to a certain extent, the signal intensity cannot be distinguished, information is lost, resulting in ranging errors and the inability to measure the reflectivity. Compared with the detection circuit of a single-photon avalanche diode without the broadening characteristic, the broadening characteristic of the present invention can obtain additional information, and it can distinguish whether an output pulse is caused by a single photon or multiple consecutive photons from the output pulse width. Therefore, the dynamic range of the single-photon avalanche diode detection circuit is increased, and pulse intensity information can still be obtained in the case of strong saturation signals. Using this information, more accurate ranging results and measurement results of the target object reflectivity can be obtained.

[0073] Second aspect

[0074] The second aspect of the present invention relates to a receiving unit 20 applicable to a lidar, including the detection circuit 10 described above and a processing unit 21, as Figure 7 shown. Figure 7 The detection circuit 10 shown in Figure 3A is the same as that shown inFigure 6A The detection circuit 10 shown above is within the protection scope of the present invention.

[0075] The specific structure and working mode of the detection circuit 10 are as described in detail above with reference to Figure 3A - 6B and will not be elaborated here. The detection circuit 10 generates a digital waveform A3 at the output end of the comparator 12 according to the incident photon excitation P. The processing unit 21 is coupled to the output end of the comparator 12 of the detection circuit 10, so it can receive this digital waveform A3 and calculate the intensity of the incident photon excitation P according to this waveform. According to an embodiment of the present invention, the processing unit 21 is configured to calculate the number of incident photons according to the pulse width of the waveform output by the comparator 12, and further obtain the reflectivity of the target object according to the calculation result.

[0076] In addition, as Figure 7 shown, the detection circuit 10 further includes a threshold control unit 15, which is coupled to the processing unit 21 and is configured to adjust the adjustable threshold signal according to the incident light intensity. The threshold control unit 15 is coupled to the first input end of the comparator 12 to provide the adjustable threshold signal Threshold to the first input end. For example, the threshold control unit 15 can increase the adjustable threshold signal as the incident light intensity increases. Preferably, the incident light intensity can be divided into multiple intervals, and each interval corresponds to an adjustable threshold signal. The higher the incident light intensity, the higher the adjustable threshold signal. The threshold control unit 15 can select an appropriate adjustable threshold signal according to the interval where the current incident light intensity is located.

[0077] Figure 8 shows a preferred embodiment according to the present invention, in which the receiving unit 20 of the lidar includes multiple groups of the detection circuits 10 and a summator 22, constituting a detection channel. Each detection circuit constitutes a pixel. Figure 8 Four pixels, namely pixel 1 - 4, are schematically shown. Those skilled in the art can easily understand that Figure 8 this is a schematic example. In a ranging circuit based on a single - photon avalanche diode array, multiple single - photon avalanche diodes are usually grouped into a channel (or called a macro - unit). In the example shown in the following figure, a channel / macro - unit includes four single - photon avalanche diodes, but the present invention is not limited thereto. A channel can be composed of any number of single - photon avalanche diodes equal to or more than one. As Figure 8As shown, the output ends of the comparators 12 of the multiple groups of detection circuits 10 are all coupled to the input end of the summer 22. The summer 22 performs a summation operation on the outputs of the multiple groups of detection circuits. The output end of the summer 22 can be connected to the processing unit 21 (not shown in the figure) for example. By using the summer 22 to perform the summation operation, the effective signals can be accumulated, so that the signal output is stronger and the signal-to-noise ratio is higher.

[0078] Preferably, by adjusting the pulse width of the single-photon signal output to match the pulse width of the lidar light emission, the signal-to-noise ratio can be further optimized and improved. Figure 8 In the circuit structure, the output digital signals of multiple pixels are subjected to an accumulation summation operation (Σ). When the accumulation result exceeds a certain numerical threshold, it is determined that there is an effective signal at this time, that is, an effective ranging echo pulse is received. The basis for this method of determining the ranging pulse signal is that the noise signals caused by ambient light or the dark count of the single-photon avalanche diode are randomly distributed on the time axis ( Figure 9 in the horizontal direction). The probability that these noise signals occur simultaneously within a very narrow time window (a few ns) is extremely low. Therefore, when multiple detection circuits 10 of single-photon avalanche diodes generate output signals (and then accumulate a relatively large value) within a very narrow time window, it is very likely that this is caused by the effective echo signal optical pulse. Furthermore, the processing circuit and the algorithm program can extract the ranging information, target reflectivity information, etc. required by the lidar through the pulse trigger time and pulse waveform after summing the output signals of multiple pixels. In the embodiment of the present invention, the threshold within a single pixel can be adjusted to adjust the width of the digital pulse signal output by this pixel. When this width is adapted to the width of the laser pulse, a more optimized ranging signal-to-noise ratio and a higher detection probability can be obtained. According to a preferred embodiment of the present invention, the threshold is adjusted so that the time width of the output digital signal of each pixel (or detection circuit) in response to a single-photon input is equal to the full width at half maximum of the laser pulse. At this time, most of the energy of the optical pulse signal emitted by the laser is concentrated within the time window corresponding to the full width at half maximum, Figure 8The processing circuit shown in sums up the single-photon counts that occur within this time window. In other words, by setting the pulse width of the output signal, the length of the integration time window is set, and the processing circuit will accumulate the single-photon events that occur within the time window. If the integration time window is set to be narrower than the laser pulse, then the emitted light energy will be wasted, and most of the effective emitted signals will not be collected, resulting in a decrease in the ranging signal-to-noise ratio and the detection probability. If the integration time window is set to be wider than the laser pulse, then the total amount of the signal does not change significantly, but the total amount of noise that enters this wider time window will increase, resulting in a decrease in the ranging signal-to-noise ratio and the detection probability. Therefore, there is an optimal integration time window width. By adjusting the pulse width of the output signal of the detection circuit of the single-photon avalanche diode, this optimal time window width can be selected, thereby obtaining an optimized ranging signal-to-noise ratio and an optimized detection probability. Therefore, by setting the adjustable threshold signal of the detection circuit such that the width of the output waveform of the comparator of the detection circuit for a single photon matches the width of the laser pulse of the lidar, the signal-to-noise ratio of the circuit can be improved. Preferably, the width of the output waveform of the comparator of the detection circuit for a single photon is equal to the full width at half maximum of the laser pulse of the lidar.

[0079] will be described in detail with reference to Figure 9 the waveform shown. Figure 9 In , the time width w of the output digital signal of each pixel (i.e., waveform A3 output by the detection circuit) is equal to the full width at half maximum of the laser pulse. As shown in the waveforms of pixels 1 - pixel 4, within this time width w, four pixels generate outputs (i.e., the rising edges of the outputs of the four pixels all fall within this time width). After being accumulated and summed by the summer 22, the height of the waveform output by the summer 22 is four times the height of the waveform of a single pixel. Since the probability that noise signals occur simultaneously within a time width w is extremely low, the output of the noise signals usually does not accumulate. Even after passing through the summer, the height of the output waveform is only one time the height of the waveform of a single pixel. In this case, the signal-to-noise ratio of the detection unit can be characterized as 4. If the threshold is further increased such that the time width w of the output digital signal of each pixel (i.e., waveform A3 output by the detection circuit) decreases, then within this time width w, the outputs generated by the four pixels cannot all be accumulated, and the height of the waveform output by the summer 22 is less than four times the height of the waveform of a single pixel. For example, it may be two times or three times. In this case, the signal-to-noise ratio decreases significantly. On the contrary, if the threshold is further decreased such that the time width w of the output digital signal of each pixel (i.e., signal waveform A3) increases, although the outputs generated by the four pixels within this time width w can all be accumulated and the height of the waveform output by the summer 22 is equal to four times the height of the waveform of a single pixel, within this time width w, the noise signals may also be accumulated through the summer. Therefore, the signal-to-noise ratio will also decrease.

[0080] The broadening characteristic can play a quite significant role in an optoelectronic system. In the detection circuits of some single-photon avalanche diodes (SPADs) without the broadening characteristic, within the time period after avalanche recovery (the typical value of the recovery time is several nanoseconds to dozens of nanoseconds), if other photons enter the photosensitive region of the SPAD, it will not cause any change in the output signal of the SPAD. It is equivalent to that the recovery time of the SPAD is the "dead time" of the detection circuit. Therefore, for the detection circuit of the SPAD without the broadening characteristic, when the echo signal is strong enough, the signal intensity cannot be distinguished, information is lost, and thus ranging errors and the inability to measure the reflectivity will occur. Compared with the detection circuit of the SPAD without the broadening characteristic, this broadening characteristic of the present invention can obtain additional information, and can distinguish whether an output pulse is caused by a single photon or multiple consecutive photons from the output pulse width. Therefore, the dynamic range of the SPAD detection circuit is increased, and pulse intensity information can still be obtained in the case of strong saturation signals. Using this information, more accurate ranging results and measurement results of the target reflectivity can be obtained.

[0081] When the receiving unit detects that the current echo signal is too strong, the threshold for SPAD inversion can also be adjusted upward to obtain more accurate information about the signal light pulse, as described above with reference to Figure 4 what has been described.

[0082] In addition, those skilled in the art understand that the above-mentioned receiving unit 20 can be used as a unit, with each unit corresponding to a channel, and arranged in an array form to form a single-photon avalanche diode detection array, constituting multiple receiving channels of a lidar for measuring incident light, and all of these are within the protection scope of the present invention.

[0083] The present invention also relates to a method for echo detection using the receiving unit as described above.

[0084] In addition, when used in lidar, the output pulse width and recovery time of the single-photon avalanche diode detection circuit are required to be as short as possible. Such optimization can make the dynamic range of the single-photon avalanche diode device larger and less likely to saturate under ambient light noise. Some designs are needed to make the output pulse width and recovery time of the single-photon avalanche diode detection circuit as short as possible. In the single-photon avalanche diode detection circuit of this patent, the recovery time, also known as the quenching time constant, is determined by the quenching resistance value and the junction capacitance of the single-photon avalanche diode. Reducing the quenching resistance value or reducing the junction capacitance of the diode can shorten the quenching time constant. If the quenching resistance value is too small, quenching may not succeed, and the lower limit is usually in the tens of kiloohms. Reducing the junction capacitance usually requires reducing the photosensitive area of a single single-photon avalanche diode, and reducing the photosensitive surface of a single single-photon avalanche diode means that more single-photon avalanche diode units can be placed under the same total photosensitive surface area, which also increases the dynamic range of a channel / macro cell (less likely to be saturated by ambient light). Therefore, according to the preferred embodiment of the present invention, in lidar applications, the photosensitive area of a single single-photon avalanche diode usually does not exceed 500um 2 .

[0085] Third aspect

[0086] Figure 10Fig. 30 shows a lidar 30 according to the third aspect of the present invention. As shown in the figure, the lidar 30 includes a transmitting unit 31 and the receiving unit 20 as described above. The transmitting unit 31 includes a laser array configured to emit a plurality of laser beams for detecting a target object OB. After the laser beams encounter the target object OB, diffuse reflection occurs, and part of the reflected echo returns to the lidar and is received by the receiving unit 20. As shown above, the receiving unit 20 includes a single-photon avalanche diode and a comparator, and can receive the echo reflected by the laser beam from the detected target object OB and convert it into a digital signal for output. Although not shown, those skilled in the art can easily understand that the transmitting unit 31 may further include a transmitting lens group located downstream of the optical path of the laser array for modulating (collimating) the laser beams emitted by the laser array into parallel light and emitting them into the ambient space around the lidar 30. Similarly, the receiving unit 20 may also include a receiving lens group, and the single-photon avalanche diode is located on its focal plane for converging the echo reflected by the emitted laser beam from the detected target object OB onto the single-photon avalanche diode. As shown in the figure, the laser beam L1 emitted by the transmitting unit 31 is projected onto the target object OB, and diffuse reflection occurs. Part of the laser beam is reflected back to form an echo L1'. The receiving unit 20 receives the reflected echo L1' and converts it into an electrical signal. The processing unit 21 of the receiving unit 20 is configured to calculate the distance and / or reflectivity of the target object according to the waveform output by the comparator of the receiving unit. For example, the processing unit 21 can calculate the distance of the target object according to the time of flight TOF of the echo (the time period from the laser emission to the single-photon avalanche diode reception) and the speed of light. Additionally or alternatively, the processing unit 21 calculates the reflectivity of the target object according to the pulse width of the signal.

[0087] Fourth aspect

[0088] The fourth aspect of the present invention provides a laser detection method 40, as Figure 11 shown, which will be described in detail below with reference to Figure 11 ...

[0089] In step S41, a detection laser beam is emitted for detecting a target object.

[0090] In step S42, an echo from the target object is received by a single-photon avalanche diode, where the single-photon avalanche diode generates a photocurrent according to incident photons.

[0091] In step S43, an electrical signal representing the photocurrent is compared with an adjustable threshold signal by a comparator to generate a digital signal output.

[0092] In step S44, the adjustable threshold signal is adjusted according to the waveform of the digital signal output.

[0093] According to a preferred embodiment of the present invention, the step of adjusting the adjustable threshold signal according to the waveform of the digital signal output includes: increasing the adjustable threshold signal as the intensity of the incident light increases. After obtaining the digital signal output of the comparator, the intensity of the incident light can be obtained according to its waveform, for example, by calculating the number of incident photons to evaluate the intensity of the incident light, and then the adjustable threshold signal can be increased simultaneously according to the increase in intensity.

[0094] The preferred embodiments of the four aspects of the present invention have been described in detail above. Through the solution of the preferred embodiment of the present invention, when the ambient light is strong, by increasing the threshold of the detection circuit, the dynamic range of the single-photon avalanche photodiode device can be increased, making it less likely to saturate. By adjusting the pulse width of the single-photon signal output to match the pulse width of the lidar light emission, an optimized signal-to-noise ratio can be achieved. Compared with the detection unit of the single-photon avalanche photodiode without the broadening characteristic, this broadening characteristic can obtain additional information, and it can be distinguished from the output pulse width whether an output pulse is caused by a single photon or multiple consecutive photons, increasing the dynamic range of the single-photon avalanche photodiode device. In the case of a strong saturation signal, the pulse intensity information can be obtained, and using this information, more accurate ranging results and measurement results of the target reflectivity can be obtained. In addition, by adjusting the pulse width of the single-photon signal output to match the pulse width of the lidar light emission, an optimized signal-to-noise ratio can be achieved.

[0095] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A receiving device for a lidar, comprising: A detector configured to receive incident light and generate a photocurrent, the detector including a single - photon avalanche diode, A detection circuit coupled to the detector, the detection circuit configured to output a pulse signal based on the photocurrent, the detection circuit having a first threshold, the first threshold configured to make the pulse width of the pulse signal related to the number of photons included in the incident light, and A processing circuit configured to determine the intensity of the incident light based on the pulse width of the pulse signal.

2. The receiving device according to claim 1, wherein When the photocurrent exceeds the first threshold, the detection circuit outputs a high level, and when the photocurrent is lower than the first threshold, the detection circuit outputs a low level.

3. The receiving device according to claim 2, wherein The detection circuit includes a comparator, a first input terminal of the comparator is coupled to the detector, a second input terminal of the comparator receives the first threshold, and an output terminal of the comparator outputs the pulse signal.

4. The receiving device according to claim 1, wherein The receiving device includes a plurality of detectors and a plurality of detection circuits, and the plurality of detectors and the plurality of detection circuits are connected in one - to - one correspondence.

5. The receiving device according to claim 1 or 4, characterized in that The processing circuit is configured to determine the intensity of the incident light based on the pulse width of the pulse signal and the single - photon pulse width.

6. The receiving device according to claim 1, characterized in that, The detector further includes a quenching resistor configured to quench the photocurrent.

7. A receiving device for a lidar, comprising: A detector configured to receive incident light and generate a photocurrent, the detector including a single - photon avalanche diode, and A detection circuit coupled to the detector, the detection circuit configured to output a pulse signal based on the photocurrent, The detection circuit has a second threshold, and the second threshold is configured to make the number of the pulse signals related to the number of photons included in the incident light.

8. The receiving device according to claim 7, wherein When the photocurrent exceeds the second threshold, the detection circuit outputs a high level, and when the photocurrent is lower than the second threshold, the detection circuit outputs a low level.

9. The receiving device according to claim 8, wherein, The detection circuit includes an inverter, an input terminal of the inverter is coupled to the detector, and an output terminal of the inverter outputs the pulse signal.

10. The receiving device according to claim 7, characterized in that, It further includes a processing circuit configured to accumulate the pulse signals within a preset time window.

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