WO2021088646A1 - Dynamic threshold timing circuit, lidar, and time information obtaining method - Google Patents

Abstract

A dynamic threshold timing circuit (100), comprising: a comparator (101) having a first input terminal, a second input terminal and an output terminal, the first input terminal being capable of receiving an external input signal, and the second input terminal being capable of receiving a detection threshold; a time-to-digital converter (102) which is coupled with an output end of the comparator (101) so as to obtain time information of an output signal of the comparator (101); and a controller (103) which is configured to be capable of receiving an external input signal, generating a detection threshold according to the external input signal, and providing the detection threshold for a second input end of the comparator (101), wherein the detection threshold is related to noise in the external input signal.

Description

Dynamic threshold timing circuit, lidar, and method for acquiring time information Technical field

The present invention generally relates to the field of circuit technology, and more particularly to a dynamic threshold timing circuit, a laser radar including the same, and a method for collecting time information of an external input signal.

Background technique

Time-to-Digital Converter (TDC) is a measuring device or equipment that digitizes time information, and a timing circuit is a circuit that extracts time information from an analog signal to be measured. An analog signal carrying time information cannot be directly used as the input of TDC. A timing circuit needs to extract the time information from the signal, output the time signal carrying time information, and send it to TDC. Time information is usually carried by the signal edge of the level transition. The output of the TDC is only the digital quantization result of the measured time signal, and other information such as amplitude and waveform other than the time information cannot be obtained.

Common timing circuits, such as leading edge timing circuits, are mainly composed of a comparator and a threshold value generating circuit, and the threshold time information of the signal to be measured is obtained through the comparator. Because the timing circuit only pays attention to the condition of the signal to be measured near the threshold voltage, it is unable to monitor the baseline, resulting in the timing circuit's lack of grasp of the baseline state (the baseline value is determined by the circuit itself and will drift with temperature). For applications with high signal-to-noise ratio, this will not cause trouble, but in applications with lower signal-to-noise ratio, such as lidar (Lidar) telemetry applications, the baseline position and noise level cannot be grasped, which will cause timing If the circuit loses its reference, the signal under test cannot be detected, or a noise trigger will be generated.

In order to obtain the baseline status, there are methods to use a timing circuit with multiple thresholds to eliminate the influence of the baseline noise of the signal under test. However, because there is no full waveform information of the baseline, a specific baseline state cannot be obtained, and the relative position of the threshold and the baseline can only be estimated from the triggering laws of different thresholds, and the magnitude of the noise can be estimated. Therefore, this method is not intuitive enough, nor can it distinguish between noise and signal in principle.

Using an analog-to-digital converter (ADC) to measure the time of the signal under test is the main method to avoid this technical problem. ADC can sample to obtain the full waveform of the signal under test, which contains baseline information. Therefore, the ADC-based time measurement method can use the digital dynamic threshold method to measure the time information of the small signal while eliminating the influence of noise. However, due to the time measurement principle of the ADC, its time measurement accuracy is related to the number of sampling points on the edge of the signal to be measured. Therefore, for high-speed signals, in order to obtain accurate time information, an ADC with an ultra-high sampling rate is required. For applications such as Lidar, it is necessary to measure high-speed signals. For example, if the rise time of the signal to be measured is 8ns, in order to ensure that there are at least 4 sampling points along the edge of the signal to be measured, the sampling frequency of the ADC is required to be 500MHz (and if the sampling rate is determined according to the sampling law, for a signal with a rise time of 8ns , Only a sampling rate of 80MHz is enough. Lidar needs to get more accurate time measurement, and the sampling rate of ADC is several times higher than that of general applications. The increase in sampling rate also greatly increases the power consumption of the circuit. The increase in circuit power consumption usually results in a large amount of heat. For lidar applications, because a large number of devices are gathered in a small space, the increase in device heat is extremely detrimental to the operation of the system.

The content of the background technology is only the technology known to the inventor, and does not of course represent the existing technology in this field.

Summary of the invention

In view of at least one defect of the prior art, the present invention provides a dynamic threshold timing circuit, including:

A comparator, the comparator having a first input terminal, a second input terminal and an output terminal, the first input terminal is adapted to receive an external input signal, and the second input terminal is adapted to receive a detection threshold;

A time-to-digital converter, the time-to-digital converter is coupled to the output terminal of the comparator to obtain time information of the output signal of the comparator;

A controller configured to receive the external input signal, generate the detection threshold value according to the external input signal, and provide the detection threshold value to a second input terminal of the comparator, wherein the detection threshold value It is related to the noise in the external input signal.

According to one aspect of the present invention, the dynamic threshold timing circuit further includes an analog-to-digital converter, the analog-to-digital converter is coupled to the controller, and the external input signal is converted by the analog-to-digital converter After that, it is provided to the controller.

According to an aspect of the present invention, the controller is configured to generate the detection threshold in the following manner:

Obtaining noise data in the external input signal;

Obtaining the mean value V _{base of} the noise data;

_{Obtain the parameter σ base that} characterizes the dispersion of the noise data; and

Determine the detection threshold according to the average value V _base and the parameter σ _base.

According to an aspect of the present invention, the parameter σ _base is the standard deviation of the noise data, and the detection threshold is (V _base +n*σ _base ), where n is a positive integer.

According to one aspect of the present invention, the dynamic threshold timing circuit further includes a digital-to-analog converter, the input of the digital-to-analog converter is coupled to the controller and receives the detection threshold, the digital-to-analog converter The output terminal of is coupled to the second input terminal of the comparator, and the detection threshold is digital-to-analog converted and then provided to the second input terminal of the comparator.

According to an aspect of the present invention, the sampling frequency of the analog-to-digital converter is less than or equal to 100 MHz.

According to an aspect of the present invention, the dynamic threshold timing circuit further includes a selection switch, the selection switch has a first position and a second position, when in the first position, the selection switch causes the external input signal to be Is coupled to the input terminal of the analog-to-digital converter, and the input terminal of the analog-to-digital converter is disconnected from the output terminal of the digital-to-analog converter; when in the second position, the selection switch enables the external The input signal is disconnected from the input terminal of the analog-to-digital converter, and the input terminal of the analog-to-digital converter is coupled to the output terminal of the digital-to-analog converter.

According to an aspect of the present invention, the controller is configured to use the analog-to-digital converter to sample the output of the digital-to-analog converter when the selector switch is in the second position, and to calibrate the detection threshold .

According to an aspect of the present invention, the controller calibrates the detection threshold in the following manner:

Controlling the digital-to-analog converter to output a first detection threshold DAC_1, and sampling the first detection threshold through the analog-to-digital converter to obtain a first detection threshold measurement value ADC_1;

Controlling the digital-to-analog converter to output a second detection threshold DAC_2, and sampling the second detection threshold through the analog-to-digital converter to obtain a second detection threshold measurement ADC_2;

The detection threshold input to the digital-to-analog converter is set to be (V _base +n*σ _base )*(DAC_2-DAC_1)/(ADC_2-ADC_1)+DAC_1.

According to one aspect of the present invention, the dynamic threshold timing circuit further includes an amplifier whose input terminal can receive the external input signal, and the output terminal is coupled to the first input terminal of the comparator and the analog signal. Digital converter, so that the external input signal is amplified by the amplifier, the amplified external input signal is provided to the first input terminal of the comparator, and the amplified external input signal is passed through the analog-to-digital converter After conversion, it is provided to the controller.

The present invention also provides a laser radar, including a photodetector and the above-mentioned dynamic threshold timing circuit;

The photodetector is suitable for receiving detection echoes reflected by obstacles;

The dynamic threshold timing circuit is coupled to the photodetector and is adapted to receive the signal output by the photodetector as the external input signal.

According to an aspect of the present invention, the lidar further includes a transmitting device, wherein the transmitting device is adapted to emit laser pulses;

The controller is coupled to the emitting device, and the controller is adapted to learn the time information of the laser pulse emitted by the emitting device, and based on the time information of the laser pulse emission and the echo received by the photodetector Time information, calculate the distance between the lidar and external obstacles.

The present invention also provides a method for collecting time information of external input signals, including:

Generating a detection threshold value according to an external input signal, wherein the detection threshold value is related to noise in the external input signal;

Comparing the external input signal with the detection threshold to generate an output signal;

Obtain the time information of the output signal.

According to an aspect of the present invention, the method further includes: performing analog-to-digital conversion on the external input signal.

According to an aspect of the present invention, the detection threshold is generated in the following manner:

Obtaining noise data in the external input signal;

Obtaining the mean value V _{base of} the noise data;

_{Obtain the parameter σ base that} characterizes the dispersion of the noise data of the external input signal; and

Determine the detection threshold according to the average value V _base and the parameter σ _base.

According to an aspect of the present invention, the parameter σbase is the standard deviation of the noise data, and the detection threshold is (V _base +n*σ _base ), where n is a positive integer.

According to an aspect of the present invention, the method further includes: performing digital-to-analog conversion of the detection threshold through a digital-to-analog converter and then providing the detection threshold to the comparator.

According to an aspect of the present invention, the sampling frequency of the analog-to-digital converter is less than or equal to 100 MHz.

According to an aspect of the present invention, the method further includes: sampling the output of the digital-to-analog converter by the analog-to-digital converter, and calibrating the detection threshold.

According to one aspect of the present invention, the detection threshold is calibrated in the following manner:

Controlling the digital-to-analog converter to output a first detection threshold DAC_1, and sampling the first detection threshold through the analog-to-digital converter to obtain a first detection threshold measurement value ADC_1;

Controlling the digital-to-analog converter to output a second detection threshold DAC_2, and sampling the second detection threshold through the analog-to-digital converter to obtain a second detection threshold measurement ADC_2;

The detection threshold input to the digital-to-analog converter is set to be (V _base +n*σ _base )*(DAC_2-DAC_1)/(ADC_2-ADC_1)+DAC_1.

According to an aspect of the present invention, the method further includes: amplifying the external input signal,

The step of generating a detection threshold value according to an external input signal includes: performing an analog-to-digital conversion on the amplified external input signal through an analog-to-digital converter;

The step of comparing the external input signal with a detection threshold includes: comparing the amplified external input signal with the detection threshold.

The embodiment of the present invention combines the advantages of low power consumption of the TDC time measurement circuit, and realizes a dynamic threshold circuit that can be dynamically calibrated. Compared with the TDC time measurement circuit with a fixed threshold, the present invention can monitor the baseline state, dynamically adjust the trigger threshold, and simultaneously realize the dynamic calibration of the threshold, which reduces the amplitude requirement of the signal to be measured. Compared with the ADC time measurement method, this method is more suitable for compact, power-constrained measurement equipment such as Lidar due to its lower power consumption.

Description of the drawings

The drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the exemplary embodiments of the present invention and the description thereof are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the attached picture:

Figure 1 shows a dynamic threshold timing circuit according to an embodiment of the present invention;

Figure 2 shows a dynamic threshold timing circuit according to a preferred embodiment of the present invention;

Figure 3 shows a typical external input signal including signal waveform data and noise data;

Figure 4 shows a dynamic threshold timing circuit according to a preferred embodiment of the present invention; and

Fig. 5 shows a method for collecting time information of an external input signal according to an embodiment of the present invention.

Detailed ways

In the following, only certain exemplary embodiments are briefly described. As those skilled in the art can realize, the described embodiments may be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the drawings and description are to be regarded as illustrative in nature and not restrictive.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", " "Back", "Left", "Right", "Straight", "Horizontal", "Top", "Bottom", "Inner", "Outer", "Clockwise", "Counterclockwise" and other directions or The positional relationship is based on the position or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the pointed device or element must have a specific orientation, be constructed and operated in a specific orientation, Therefore, it cannot be understood as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more than two, unless otherwise specifically defined.

In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection. Connected or integrally connected: It can be mechanically connected, or electrically connected or can communicate with each other; it can be directly connected or indirectly connected through an intermediate medium, which can be the internal communication of two components or the interaction of two components relationship. For those of ordinary skill in the art, the specific meanings of the above-mentioned terms in the present invention can be understood according to specific situations.

In the present invention, unless otherwise clearly defined and defined, the first feature "on" or "under" the second feature may include the first and second features in direct contact, or may include the first and second features Not in direct contact but through other features between them. Moreover, the "above", "above" and "above" of the first feature on the second feature include the first feature directly above and obliquely above the second feature, or it simply means that the first feature is higher in level than the second feature. The “below”, “below” and “below” of the first feature of the second feature include the first feature directly above and obliquely above the second feature, or it simply means that the level of the first feature is smaller than the second feature.

The following disclosure provides many different embodiments or examples for realizing different structures of the present invention. In order to simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are only examples, and are not intended to limit the 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 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.

The preferred embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described here are only used to illustrate and explain the present invention, and are not used to limit the present invention.

FIG. 1 shows a dynamic threshold timing circuit 100 according to an embodiment of the present invention, which will be described in detail below with reference to FIG. 1.

As shown in FIG. 1, the dynamic threshold timing circuit 100 includes a comparator 101, a time-to-digital converter 102 and a controller 103. Wherein, the comparator 101 has a first input terminal (as shown in Fig. 1 in the same direction input terminal +), a second input terminal (as shown in Fig. 1 the inverting input terminal of the comparator 101 -) and an output terminal. Wherein, the first input terminal can receive an external input signal. The external input signal can be, for example, a signal output by a photodetector of a lidar (such as an avalanche photodiode APD). The dynamic threshold timing circuit 100 can be used to obtain the external input. The time information of the signal; the second input can receive the detection threshold. According to an embodiment of the present invention, when the external input signal is higher than the detection threshold, the output terminal of the comparator 101 outputs a high level; when the external input signal is lower than the detection threshold, the output The output terminal of the comparator 101 outputs a low level. Those skilled in the art can easily understand that the opposite arrangement is also feasible.

The time-to-digital converter 102 is coupled to the output terminal of the comparator 101 to obtain time information of the timing signal output by the comparator. The signal output by the comparator 101 carries time information during the high-level and low-level transitions. The time-to-digital converter 102 can obtain the time point of the high and low level transition, that is, obtain the digitized time information, and output the digitized time information, for example, to the controller 103. The controller 103 calculates the distance between the lidar and the external obstacle by using the time-of-flight method (TOF), for example, based on the time information of laser pulse emission and the time information of the echo (ie, external input signal) received by the photodetector.

The controller 103 is configured to receive the external input signal, generate the detection threshold value according to the external input signal, and provide the detection threshold value to the second input terminal of the comparator 101. As shown in Figure 1, in addition to being sent to the first input terminal of the comparator 101, the external input signal is also sent to the first port 1031 of the controller 103, and the controller 103 generates according to the external input signal. The detection threshold is detected, and the detection threshold is provided to the second input terminal of the comparator 101 through the second port 1032.

In the present invention, the detection threshold is related to the noise in the external input signal, for example, is related to the mean value of the noise data, the dispersion degree of the noise data, and other parameters. In this way, the detection threshold can be dynamically adjusted during the operation of the circuit, so that the comparison threshold of the comparator is dynamically adjusted according to the noise in the external input signal, so even in applications with a lower signal-to-noise ratio, such as lasers In the distance measurement application of radar (Lidar), it will not cause false triggering of noise, so that the time information of the tiny signal can be obtained accurately.

Fig. 2 shows a schematic circuit diagram of a dynamic threshold timing circuit 100 according to a preferred embodiment of the present invention. This is described in detail below with reference to FIG. 2.

As shown in FIG. 2, according to a preferred embodiment of the present invention, the dynamic threshold timing circuit 100 further includes an analog-to-digital converter (ADC) 104. As shown in FIG. 2, the external input signal is also coupled to the input terminal of the analog-to-digital converter 104, and the output terminal of the analog-to-digital converter 104 is coupled to the first port 1031 of the controller 103, Therefore, the external input signal is provided to the controller 103 after the analog-to-digital converter 104 performs analog-to-digital conversion.

As described above, the detection threshold is related to the noise in the external input signal. The method for obtaining the detection threshold according to a preferred embodiment of the present invention is described below.

After receiving the external input signal, the controller 103 may generate the detection threshold in the following manner:

Step 1: Obtain noise data in the external input signal. After the controller 103 receives the sampled data of the analog-to-digital converter 104, it can remove the signal waveform data in the sampled data (for example, using a priori preset threshold for removing the signal waveform data), and only keep the external input signal Noise data.

Figure 3 is a typical external input signal including signal waveform and noise. The horizontal axis is time and the vertical axis is amplitude. The corresponding calculation is performed after multiple sampling by the analog-to-digital converter. This noise is called baseline noise, and its average value is Reflects the baseline value, and its standard deviation reflects the intensity of the baseline noise. When removing the signal waveform data in the sampled data, the signal waveform data of the external input signal whose amplitude is higher than the preset threshold can be removed according to the preset threshold. The threshold can also be selected according to the measured scene. For example, when the measurement is performed during the day, the preset threshold can be set to be higher to retain as much noise data as possible; when the measurement is performed at night, the preset threshold can be set to be lower, so that as much as possible Ground removal of signal waveform data. In addition, the “removal of the signal waveform data in the sampled data” in the present invention does not necessarily remove all the signal waveform data in the sampled data, and some signal waveform data with lower amplitude (close to noise) can also be retained. These are all within the protection scope of the present invention. Step 2: Obtain the mean value V _{base of} the noise data. On the basis of the noise data obtained in step 1, for example, by averaging the noise data data, the mean value V _{base of the} noise data can be obtained.

Step 3: Obtain a parameter σ _{base that} characterizes the dispersion of the noise data. On the basis of the noise data obtained in step 1, a parameter σ _base that can characterize its dispersion is obtained, and the parameter may be, for example, the standard deviation of the noise data.

Step 4: Determine the detection threshold according to the average value V _base and the parameter σ _base. According to a preferred embodiment of the present invention, when the parameter σ _base is the standard deviation of the noise data, the detection threshold is V _base +n*σ _base , where n is a positive integer.

When measuring a signal with a low signal-to-noise ratio, in order to make full use of the signal-to-noise ratio, the controller calculates the lowest threshold of the low-noise false trigger probability. For lidar applications, ambient light noise is the main noise in light scenarios. Ambient light noise is a kind of shot noise, which conforms to the Poisson distribution. When the mean value of the Poisson distribution is high, it can be approximated as a Gaussian distribution, with the mean value λ and the standard deviation

Therefore, the relationship between the probability of noise crossing and the threshold voltage can be obtained according to the Gaussian distribution model. Suppose that in order to realize that the false trigger probability of noise is lower than p, the trigger threshold needs to be set to be greater than or equal to nσ (the setting of n needs to consider the single pulse/multi-pulse transmission of lidar at the same time). The controller can then calculate that the detection threshold should be set to V _base +n*σ _base . The controller provides the calculation result to the comparator to realize the signal timing measurement of the dynamic threshold.

According to a preferred embodiment of the present invention, as shown in FIG. 2, the dynamic threshold timing circuit 100 further includes a digital-to-analog converter (DAC) 105. The input terminal of the digital-to-analog converter 105 and the second of the controller 103 The port 1032 is coupled to and receives the detection threshold, the output terminal of the digital-to-analog converter 105 is coupled to the second input terminal of the comparator 101, and the detection threshold is digital-to-analog converted and provided to the comparison The second input terminal of the 器101. As mentioned above, the controller can calculate that the detection threshold should be set to V _base +n*σ _base . The controller sends the digital sequence for which the detection threshold should be set as the setting value of the digital-to-analog converter DAC to the digital-to-analog converter. The threshold voltage output by the digital-to-analog converter is connected to the comparator through the driver, and the signal timing measurement of the dynamic threshold can be realized.

In the embodiment of FIG. 2, the controller 103 can dynamically update the detection threshold according to the noise condition of the external input signal, so as to provide the comparator 101 with a reference for comparison.

In an embodiment of the present invention, the analog-to-digital converter 105 may perform sampling at a lower sampling rate, for example, its sampling frequency may be less than or equal to 100 MHz, which is much lower than the 500 MHz required in the prior art. Applications such as lidar are extremely advantageous. Assuming that the noise of the external input signal conforms to the Gaussian distribution, the mean value is μ, the standard deviation is σ, and it is sampled N times, the sampled mean value obtained conforms to the Gaussian distribution, the mean value is also μ, and the standard deviation is

That is, the higher the sampling number of Gaussian random numbers, the smaller the sampling error, and the more the sampling mean can reflect the true distribution mean. When N>25, it can be approximately considered that the sampling standard deviation obeys the mean σ, and the standard deviation is

Gaussian distribution. From this, it can be calculated how large the number of samples should be selected to meet sufficient baseline mean and baseline standard deviation measurement accuracy. For example, when the number of samples reaches 50, the mean measurement error is ±28.3%σ (95.4% confidence level), and the standard deviation measurement error is ±20.1% (95.4% confidence level); when the number of samples reaches 100, the mean measurement error is ±20%σ (95.4% confidence level), the measurement error of the standard deviation is ±14.2% (95.4% confidence level). So 50 to 100 samples can reach a considerable accuracy. Assuming that one measurement time is 1us (50-100 times of ADC sampling for one measurement), an ADC of 50MHz to 100MHz can be selected for measurement. Compared with the 500M sampling frequency of the prior art, the frequency is significantly reduced, thus greatly reducing power consumption.

Fig. 4 shows a dynamic threshold timing circuit 100 according to a preferred embodiment of the present invention. The following focuses on the differences from the embodiment in FIG. 2.

As shown in FIG. 4, the dynamic threshold timing circuit 100 further includes a selection switch 106, such as a single-pole double-throw switch. The selection switch 106 has a first position and a second position. When in the first position, the selection switch 106 enables the external input signal to be coupled to the input terminal of the analog-to-digital converter 104, and the analog-to-digital converter 104 The input terminal of the DAC is disconnected from the output terminal of the digital-to-analog converter 105; when in the second position, the selector switch 106 causes the external input signal to be disconnected from the input terminal of the analog-to-digital converter 104, so The input terminal of the analog-to-digital converter 104 is coupled to the output terminal of the digital-to-analog converter 105. The selector switch 106 is shown in the first position in FIG. 4. When in the first position, the working mode of the dynamic threshold timing circuit 100 is basically the same as the solution shown in FIG. 2. Although not shown in the figure, those skilled in the art can easily understand that the selection switch 106 can be controlled by the controller 103 to switch between the first position and the second position. In addition, the dynamic threshold timing circuit 100 further includes an ADC driver and a DAC driver. After receiving the detection threshold, the digital-to-analog converter 105 performs digital-to-analog conversion, and then, after being driven by the DAC driver, it is sent to the second input terminal of the comparator 101 as a reference for comparison. After the external input signal is driven by the ADC driver, it is provided to the analog-to-digital converter 104 for analog-to-digital conversion, and then is provided to the first port 1031 of the controller 103. I won't repeat them here.

The inventor of the present invention found that because the ADC driver, DAC driver, and baseline values all have certain deviations and temperature drifts, the scales of the analog-to-digital converter 104 and the digital-to-analog converter 105 are inconsistent, so the detection threshold is opened loop If set, the accuracy of the detection threshold cannot be guaranteed. The solution of the embodiment of FIG. 4 can calibrate the detection threshold setting. As shown in FIG. 4, when the selector switch 106 is in the second position, the output terminal of the digital-to-analog converter 105 is connected to the input terminal of the analog-to-digital converter 104, and the detection threshold output by the digital-to-analog converter can be sampled. . Because the threshold has less noise, it is possible to measure an accurate threshold with a smaller number of samples. The calibration process is as follows: first, the controller controls the digital-to-analog converter to output the first detection threshold DAC_1, and then controls the selector switch to switch to the second position within a short period of time, and collects the first detection threshold through the analog-to-digital converter 104 A detection threshold is output, and the first detection threshold measurement value ADC_1 is obtained. When the next threshold measurement window is reached, the controller sets the digital-to-analog converter 105 to output the second detection threshold DAC_2, and similarly, the second detection threshold measurement ADC_2 is obtained through the analog-to-digital converter 104. Therefore, it can be calculated that when the mean value of the measured noise data is V _base and the standard deviation of the noise is σ _base , the detection threshold set by the controller should be (V _base +n*σ _base )*(DAC_2-DAC_1)/( ADC_2-ADC_1)+DAC_1. In this way, real-time calibration is performed before the detection threshold is sent to the comparator, which can eliminate the detection threshold setting deviation caused by offset, temperature drift and inconsistent scale.

Therefore, in the solution of the embodiment in FIG. 4, the controller can control that when the selector switch 106 is in the second position, the analog-to-digital converter 104 is used to sample the output of the digital-to-analog converter 105 , Calibrate the detection threshold.

As shown in FIG. 4, the dynamic threshold timing circuit 100 further includes an amplifier 104 for amplifying the external input signal. Those skilled in the art can easily understand that the amplifier 104 usually performs equal-scale amplification. The amplified external input signal and the original external input signal only have a change in amplitude, and can still be regarded as the same signal. The input terminal of the amplifier 104 can receive the external input signal, and the output terminal is coupled to a subsequent circuit for providing an amplified external input signal, for example, to the controller. The output terminal of the amplifier 104 is also coupled to the first input terminal of the comparator 101.

In addition, those skilled in the art can easily understand that the amplifier 104 is not a necessary circuit component of the dynamic threshold timing circuit 100. For example, when the external input signal is a voltage signal and the intensity is moderate, the amplifier 104 can be omitted. In addition, according to a preferred embodiment of the present invention, if the external input signal is a current signal, such as a current signal output by a photodetector, the amplifier 104 may be a transimpedance amplifier (TIA), thereby converting the current signal into Voltage signal.

The present invention also provides a laser radar, including a photodetector and the dynamic threshold timing circuit 100 shown in FIG. 1, FIG. 2, and FIG. 4. The photodetector is suitable for receiving detection echoes reflected by obstacles. The dynamic threshold timing circuit is coupled to the photodetector and is adapted to receive the signal output by the photodetector as the external input signal.

In addition, the lidar may also include a transmitting device suitable for emitting laser pulses. The controller is coupled to the emitting device, and the controller is adapted to learn the time information of the laser pulse emitted by the emitting device, and based on the time information of the laser pulse emission and the echo received by the photodetector Time information, calculate the distance between the lidar and external obstacles.

The present invention also provides a method 200 for collecting time information of an external input signal. The method 200 can be implemented by, for example, the dynamic threshold timing circuit 100 shown in FIGS. 1, 2, and 4. This is described in detail below with reference to FIG. 5.

As shown in FIG. 5, in step 201: a detection threshold is generated according to an external input signal, where the detection threshold is related to noise in the external input signal.

For example, the detection threshold may be generated in the following manner: obtaining the noise data in the external input signal; obtaining the mean value V _{base of the noise data; obtaining the parameter σ base} representing the dispersion of the noise data of the external input signal; And determining the detection threshold according to the average value V _base and the parameter σ _base. According to a preferred embodiment of the present invention, the parameter σ _base is the standard deviation of the noise data, and the detection threshold is V _base +n*σ _base , where n is a positive integer.

In step 202: compare the external input signal with the detection threshold to generate an output signal. After using a comparator to compare the external input signal with the detection threshold, a high and low level jump can be generated, which contains the time information of the external input signal.

At step 203: Obtain the time information of the output signal.

The time-to-digital converter can obtain digitized time information according to the jump of the high and low pulses.

According to an aspect of the present invention, the method further includes: performing analog-to-digital conversion of the external input signal through an analog-to-digital converter, and then using it to generate the detection threshold. Especially when the external input signal is an analog signal, it is often necessary to perform analog-to-digital conversion first to form a digital signal, and then use it to generate a detection threshold.

In addition, according to an aspect of the present invention, the method further includes: performing digital-to-analog conversion of the detection threshold through a digital-to-analog converter and then providing the detection threshold to the comparator.

With the method of the present invention, the sampling frequency of the analog-to-digital converter can be made less than or equal to 100MHz. Compared with the sampling frequency of 500MHz in the prior art, the sampling frequency of the analog-to-digital converter in the present invention is significantly reduced, so that the amount of heat is generated. And power consumption is also significantly improved.

According to one aspect of the present invention, the method further includes sampling the output of the digital-to-analog converter by the analog-to-digital converter, and calibrating the detection threshold. For example, the detection threshold can be calibrated in the following manner:

Controlling the digital-to-analog converter to output a first detection threshold DAC_1, and sampling the first detection threshold through the analog-to-digital converter to obtain a first detection threshold measurement value ADC_1;

Controlling the digital-to-analog converter to output a second detection threshold DAC_2, and sampling the second detection threshold through the analog-to-digital converter to obtain a second detection threshold measurement ADC_2;

The detection threshold input to the digital-to-analog converter is set to be (V _base +n*σ _base )*(DAC_2-DAC_1)/(ADC_2-ADC_1)+DAC_1.

Exceptionally, in the method 200, the external input signal may be amplified first, and then used to generate the detection threshold and for comparison after the amplification. Therefore, the step of generating the detection threshold value according to the external input signal includes: performing analog-to-digital conversion of the amplified external input signal through an analog-to-digital converter; and the step of comparing the external input signal with the detection threshold value includes: The external input signal is compared with the detection threshold.

The embodiment of the present invention solves the technical problem that the time measurement circuit based on the time-to-digital converter cannot measure the tiny signal while eliminating the false trigger of noise.

Take the Lidar application based on avalanche photodiodes (APD) as an example. Lidar's light noise intensity is not static. The higher the ambient light power in the detector's field of view, the stronger the ambient light noise. Specifically, the standard deviation of ambient light noise can be approximately calculated as: i _n =√2q×I _DB ×M ² ×F×B. Where q is the electron charge constant, I _DB is the photoelectric reaction current of the APD, M is the gain of the APD, F is the additional noise figure, and B is the system bandwidth. The stronger the ambient light intensity entering the photosensitive surface of the APD, the _{larger the I DB} and the stronger the noise. Therefore, in order for the false trigger probability of noise to be lower than p in any environment, the fixed threshold must be set to n×in _,max ×G, where n is the normal distribution N(0,in _,max ) x satisfies the n value of P(x>ni _n,max )<p, i _n,max is the maximum photoelectric reaction current generated by ambient light energy, and G is the circuit gain; or use a dynamic threshold, so that the threshold is set to n×i _n × G, where i _n is the photoelectric reaction current generated by ambient light on the APD at any time. In the former of the two methods, since the signal amplitude is also required to exceed the threshold in low ambient light conditions to achieve detection, it will waste active luminescence energy in low ambient light conditions and reduce the efficiency of the detector. There are two main low ambient light conditions: one is the low power of the ambient light source-such as cloudy or night, and the other is the low reflectivity of the target object-such as detecting tires. In particular, when the low ambient light conditions belong to the latter, Lidar needs more energy to make the detection signal trigger the threshold, which will increase the power consumption of laser emission. The second dynamic threshold setting method can lower the trigger threshold when the noise is low, and the detector signal amplitude requirement is reduced accordingly, which avoids the waste of emission energy and improves the efficiency of the detector.

Since the analog-to-digital converter collects the full waveform of the signal to be measured, the time measurement circuit based on the analog-to-digital converter realizes the time measurement of the signal to be measured is completely digital. Therefore, it is very convenient to deploy a dynamically adjusted threshold on a time measurement circuit based on an analog-to-digital converter. However, as described in the previous article, the time measurement circuit based on a single analog-to-digital converter has a sampling frequency of the analog-to-digital converter that is much higher than twice the signal Nyquist frequency and much higher than the frequency required to meet the baseline sampling accuracy. The power consumption of the analog-to-digital converter is positively related to the sampling frequency. Therefore, in order to achieve the same time measurement accuracy, the analog-to-digital converter time measurement method alone needs to consume more power, which is not suitable for the application of compact equipment.

The invention combines the advantages of low power consumption of the TDC time measurement circuit, and realizes a dynamic threshold circuit that can be dynamically calibrated. Compared with the TDC time measurement circuit with a fixed threshold, the present invention can monitor the baseline state and the noise level, dynamically adjust the trigger threshold, and realize the dynamic calibration of the threshold at the same time, which reduces the amplitude requirement of the signal to be measured. Compared with the time measurement method that uses the analog-to-digital converter alone, this method is more suitable for compact, power-constrained measurement equipment such as Lidar due to lower power consumption.

The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the present invention. Within the scope of protection.

Finally, it should be noted that the above descriptions are only 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, it is still for those skilled in the art. The technical solutions described in the foregoing embodiments may be modified, or some of the technical features may be equivalently replaced. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (20)

1. A dynamic threshold timing circuit, including:

   A comparator, the comparator having a first input terminal, a second input terminal and an output terminal, the first input terminal is adapted to receive an external input signal, and the second input terminal is adapted to receive a detection threshold;

   A time-to-digital converter, the time-to-digital converter is coupled to the output terminal of the comparator to obtain time information of the output signal of the comparator;

   A controller configured to receive the external input signal, generate the detection threshold value according to the external input signal, and provide the detection threshold value to a second input terminal of the comparator, wherein the detection threshold value It is related to the noise in the external input signal.
2. The dynamic threshold timing circuit according to claim 1, further comprising an analog-to-digital converter, the analog-to-digital converter is coupled to the controller, and the external input signal is converted by the analog-to-digital converter and then Provided to the controller.
3. The dynamic threshold timing circuit according to claim 2, wherein the controller is configured to generate the detection threshold in the following manner:

   Obtaining noise data in the external input signal;

   Obtaining the mean value V _{base of} the noise data;

   _{Obtain the parameter σ base that} characterizes the dispersion of the noise data; and

   Determine the detection threshold according to the average value V _base and the parameter σ _base.
4. The dynamic threshold timing circuit according to claim 3, wherein the parameter σ _base is the standard deviation of the noise data, and the detection threshold is (V _base +n*σ _base ), where n is a positive integer.
5. The dynamic threshold timing circuit according to claim 2, further comprising a digital-to-analog converter, the input of the digital-to-analog converter is coupled with the controller, and the detection threshold is received, and the output of the digital-to-analog converter The terminal is coupled to the second input terminal of the comparator, and the detection threshold is digital-to-analog converted and then provided to the second input terminal of the comparator.
6. The dynamic threshold timing circuit according to claim 2, wherein the sampling frequency of the analog-to-digital converter is less than or equal to 100 MHz.
7. The dynamic threshold timing circuit according to claim 5, further comprising a selection switch, the selection switch has a first position and a second position, when in the first position, the selection switch enables the external input signal to be coupled To the input terminal of the analog-to-digital converter, the input terminal of the analog-to-digital converter is disconnected from the output terminal of the digital-to-analog converter; when in the second position, the selection switch makes the external input signal Disconnected from the input terminal of the analog-to-digital converter, and the input terminal of the analog-to-digital converter is coupled to the output terminal of the digital-to-analog converter.
8. The dynamic threshold timing circuit according to claim 7, wherein the controller is configured to use the analog-to-digital converter to sample the output of the digital-to-analog converter when the selector switch is in the second position , Calibrate the detection threshold.
9. 8. The dynamic threshold timing circuit according to claim 8, wherein the controller calibrates the detection threshold in the following manner:

   Controlling the digital-to-analog converter to output a first detection threshold DAC_1, and sampling the first detection threshold through the analog-to-digital converter to obtain a first detection threshold measurement value ADC_1;

   Controlling the digital-to-analog converter to output a second detection threshold DAC_2, and sampling the second detection threshold through the analog-to-digital converter to obtain a second detection threshold measurement ADC_2;

   The detection threshold input to the digital-to-analog converter is set to be (V _base +n*σ _base )*(DAC_2-DAC_1)/(ADC_2-ADC_1)+DAC_1.
10. The dynamic threshold timing circuit according to any one of claims 2-9, further comprising an amplifier, the input terminal of the amplifier can receive the external input signal, and the output terminal is coupled to the first input terminal of the comparator And the analog-to-digital converter, so that the external input signal is amplified by the amplifier, the amplified external input signal is provided to the first input terminal of the comparator, and the amplified external input signal is passed through the After conversion by the analog-to-digital converter, it is provided to the controller.
11. A laser radar, comprising a photodetector and the dynamic threshold timing circuit according to any one of claims 1-10;

    The photodetector is suitable for receiving detection echoes reflected by obstacles;

    The dynamic threshold timing circuit is coupled to the photodetector and is adapted to receive the signal output by the photodetector as the external input signal.
12. The lidar according to claim 11, further comprising a transmitting device, wherein:

    The emitting device is suitable for emitting laser pulses;

    The controller is coupled to the emitting device, and the controller is adapted to learn the time information of the laser pulse emitted by the emitting device, and based on the time information of the laser pulse emission and the echo received by the photodetector Time information, calculate the distance between the lidar and external obstacles.
13. A method for collecting time information of external input signals, including:

    Generating a detection threshold according to an external input signal, wherein the detection threshold is related to noise in the external input signal;

    Comparing the external input signal with the detection threshold to generate an output signal;

    Obtain the time information of the output signal.
14. The method according to claim 13, further comprising: performing analog-to-digital conversion on the external input signal.
15. The method according to claim 14, wherein the detection threshold is generated in the following manner:

    Obtaining noise data in the external input signal;

    Obtaining the mean value V _{base of} the noise data;

    _{Obtain the parameter σ base that} characterizes the dispersion of the noise data of the external input signal; and

    Determine the detection threshold according to the average value V _base and the parameter σ _base.
16. The method according to claim 15, wherein the parameter σ _base is the standard deviation of the noise data, and the detection threshold is (V _base +n*σ _base ), where n is a positive integer.
17. The method according to claim 14, further comprising: performing digital-to-analog conversion of the detection threshold value through a digital-to-analog converter and then providing it to the comparator.
18. The method according to claim 14, wherein the sampling frequency of the analog-to-digital converter is less than or equal to 100 MHz.
19. The method according to claim 17, further comprising: sampling the output of the digital-to-analog converter with the analog-to-digital converter to calibrate the detection threshold.
20. The method according to claim 19, wherein the detection threshold is calibrated by:

    Controlling the digital-to-analog converter to output a first detection threshold DAC_1, and sampling the first detection threshold through the analog-to-digital converter to obtain a first detection threshold measurement value ADC_1;

    Controlling the digital-to-analog converter to output a second detection threshold DAC_2, and sampling the second detection threshold through the analog-to-digital converter to obtain a second detection threshold measurement ADC_2;

    The detection threshold input to the digital-to-analog converter is set to be (V _base +n*σ _base )*(DAC_2-DAC_1)/(ADC_2-ADC_1)+DAC_1.

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