A method and system for processing fmcw lidar signals

Abstract

The application provides a kind of FMCW laser radar signal processing method and system, method includes: the laser signal generated by laser is divided into measurement light signal and local light signal;Input measurement light signal to light modulator, modulate by modulated sine wave sweep signal;Amplify modulated measurement light signal, emit to the detection target by circulator, collimating mirror, receive reflected signal;Coupling with reflected signal, enhance the energy of signal light, carry out photoelectric signal conversion;Amplify converted electrical signal, carry out electrical mixing in mixer, output intermediate frequency signal;Low-pass filter processing is carried out to intermediate frequency signal;In signal processing system, intermediate frequency signal is converted into pulse square wave by high-speed comparator, carries out capacitance analog interpolation processing, measures intermediate frequency signal period, calculates intermediate frequency signal frequency value.The application solves the technical problem that the counting error of ±1 word leads to the period of to-be-measured intermediate frequency signal, the distance calculation precision of detection target is low.

Description

Technical Field

[0001] This invention relates to the field of lidar signal processing method design, and specifically to an FMCW lidar signal processing method. Background Technology

[0002] FMCW (Frequency Modulated Continuous Wave) lidar, as a novel high-precision non-contact ranging technology, is based on the frequency modulation of continuous light. It calculates the target distance by analyzing the frequency shift information of the echo signal. Compared to traditional pulse lidar, it offers advantages such as high ranging accuracy and unambiguous distance measurement. With advancements in laser and optoelectronic device manufacturing processes, FMCW lidar has experienced rapid development and found widespread applications in both military and civilian fields. However, extracting detailed distance information places higher demands on the signal processing algorithms and systems of FMCW lidar.

[0003] FMCW lidar originated from frequency-modulated laser ranging technology and has evolved from pulsed FMCW and analog FMCW to all-digital FMCW. Early FMCW systems were primarily used in the military field. With advancements in lidar core components, especially the application of high-speed digital signal processing chips, FMCW technology has rapidly penetrated various civilian applications. For example, automotive lidar is one indication of the maturity of FMCW technology. Simultaneously, FMCW technology itself has been continuously optimized, from single-channel FMCW to multi-channel reception, and from mechanical scanning to phased array. These developments have provided FMCW lidar with stronger imaging capabilities and better real-time performance. For instance, the existing invention patent application document CN102788980A, entitled "A Frequency-Modulated Continuous Wave Automotive Collision Avoidance Radar System," includes: a radar sensor, a filter, an automatic gain control amplifier, an analog-to-digital converter, a digital signal processor, and a corresponding warning device. The signal obtained after passing through the radar sensor contains leaked modulation signals, intermediate frequency signals, and high-frequency signals. The filter removes the leaked modulation waves and high-frequency components. In digital signal processing, FFT is used for spectrum analysis to convert frequency measurement results into distance and velocity information. Different alarm methods are applied based on the measurement results. However, the analysis of fine features of echo signals presents a greater challenge. For example, the existing invention patent application document CN112099038A, entitled "A Multi-Object Recognition Method and Device Based on FMCW LiDAR," describes a method that includes: sampling K points in the time domain of a single chirped period; calculating the spectrum of K points using FFT; if the spectrum of a single chirped period has two or more difference frequencies, dividing K points into N time windows according to the sampling order, with each time window including M points; performing FFT calculation on the sampling sequence within each time window to obtain an independent spectrum, identifying windows with additional difference frequencies; analyzing the characteristics of windows with additional difference frequencies and the preceding and following windows; and determining the sequence and positional relationship of the scanned multi-target objects based on the changing pattern of the number of difference frequencies, and calculating the distance and velocity values ​​of the multi-target objects. However, the aforementioned traditional FFT-based spectrum analysis method suffers from problems such as large errors and limited distance resolution. Furthermore, the requirements for digital echo signals are increasing, and low-precision ADCs are struggling to meet ranging needs. To achieve higher distance resolutions, such as centimeter-level or even millimeter-level, the signal processing methods and architecture of FMCW lidar require improvement and innovation.

[0004] In summary, the existing technology has a counting error of ±1 digit, which leads to low accuracy in calculating the period of the intermediate frequency signal under test and the distance to the target. Summary of the Invention

[0005] The technical problem to be solved by this invention is: how to solve the technical problem that the counting error of ±1 word exists in the prior art, which leads to low accuracy in calculating the period of the intermediate frequency signal under test and the distance of the target.

[0006] The present invention solves the above-mentioned technical problems by adopting the following technical solution: An FMCW lidar signal processing method includes:

[0007] S1. A laser signal is generated using a laser, and the laser signal is divided and processed according to a first preset ratio through a first proportional coupler to obtain a measurement optical signal and a first local oscillator optical signal.

[0008] S2. Input the measurement optical signal to the optical modulator, use the signal generator to generate a modulated sine wave sweep signal, and modulate the measurement optical signal to obtain the modulated measurement optical signal.

[0009] S3. Amplify and modulate the measurement light signal to obtain the amplified measurement light signal. Use a circulator and collimating lens to transmit the collimated measurement light signal to the detection target and receive the reflected measurement light signal.

[0010] S4. Using the second proportional coupler, the reflected measurement light signal and the first local oscillator light signal are coupled and processed according to the second preset ratio to obtain the energy-enhanced light signal. The energy-enhanced light signal is then input to the balanced detector for photoelectric signal conversion to obtain the converted electrical signal.

[0011] S5. The converted electrical signal is amplified and processed using a transimpedance amplifier. The second local oscillator signal generated by the signal generator is used to perform electrical mixing operation on the converted electrical signal and the second local oscillator signal in the mixer to obtain and output the intermediate frequency signal.

[0012] S6. Perform low-pass filtering on the intermediate frequency signal to remove the high-frequency mixing components in the intermediate frequency signal and obtain a low-pass filtered signal. Use a signal processing system to perform capacitor-based analog interpolation on the low-pass filtered signal. The signal processing system includes: a first high-speed comparator Comp1, a second high-speed comparator Comp2, AND gates, NOT gates, a first constant current source CS1, a second constant current source CS2, an integrating capacitor, and a timer.

[0013] S7. Measure the period of the low-pass filter signal, calculate the intermediate frequency signal value based on the period, and obtain the current time value T0 by counting N0 pulses within T0.

[0014] This invention proposes a novel hardware architecture and intermediate frequency (IF) calculation method based on the traditional FMCW lidar pulse measurement method, combined with capacitance analog interpolation. This enables high-precision and high-efficiency FMCW lidar signal measurement. Therefore, the FCMW lidar signal processing method designed in this paper has significant advantages and application prospects in terms of architecture, cost, and detection accuracy. This invention achieves high-precision IF signal measurement of FMCW lidar through a simple architecture, offering advantages such as low cost and high resolution.

[0015] In a more specific technical solution, in S1, the laser includes: a distributed feedback laser and a vertical cavity surface-emitting laser.

[0016] In a more specific technical solution, S1 includes:

[0017] S11. Allow the local oscillator optical signal to enter the first input port of the second proportional coupler;

[0018] S12. Allow the measurement optical signal to enter the optical modulator and supply an external bias voltage to the optical modulator;

[0019] S13. Use a signal generator to generate a sinusoidal sweep frequency modulation wave, and send the sinusoidal sweep frequency modulation wave to the optical modulator and the back-end circuit mixer respectively.

[0020] In a more specific technical solution, S3 includes:

[0021] S31. The measurement optical signal is amplified and processed using an erbium-doped fiber amplifier (EDFA) to obtain the amplified measurement optical signal.

[0022] S32. The measurement optical amplification signal is input into the first port of the circulator, and the circulator output signal is output from the second port of the circulator.

[0023] S33. The output signal of the circulator is fed into the collimating lens. The collimating lens is used to collimate the output signal of the circulator to obtain and emit the collimated light signal to the detection target.

[0024] S34. The reflected light signal is detected by the target. The reflected light signal enters the collimating lens, enters from the second port of the circulator, and exits from the third port of the circulator.

[0025] In a more specific technical solution, S4 includes:

[0026] S41. Using a balanced detector, the energy-enhanced optical signal is converted into an electrical signal;

[0027] S42. Using a balanced detector, DC component elimination and common-mode noise elimination operations are performed on the energy-enhanced optical signal.

[0028] In a more specific technical solution, S6 includes:

[0029] S61. Using the first high-speed comparator Comp1, the intermediate frequency signal f x Perform pulse square wave conversion to obtain the square wave intermediate frequency signal;

[0030] S62. Input the square wave intermediate frequency signal to the first port of the AND gate, so that the preset frequency reference clock signal will enter the second port of the AND gate through an NOT gate to obtain the AND gate output signal, so as to adjust the switching state of the first switch S1 and the second switch S2.

[0031] S63. Based on the switch state, control the charging and discharging operations of the first constant current source CS1 and the second constant current source CS2 on the integrating capacitor C1.

[0032] This invention employs a capacitor deployed after a transimpedance amplifier (TIA) and a high-speed comparator. After the comparator converts the intermediate frequency signal waveform into a square wave, the charging and discharging process of the capacitor is controlled by a logic circuit. A timer records the time information of the intermediate frequency signal. Then, the waveform information is broadened during the capacitor discharge process, and a high-precision counter is used to count the pulses within one cycle to finally measure the frequency of the waveform, thereby improving the accuracy of the distance information of the FMCW lidar.

[0033] In a more specific technical solution, S63 also includes:

[0034] S631, based on the capacitor's discharge time mT a Charging time (mT) b The time interval T is obtained by using the following logic:

[0035] T = T0 + T a -T b (1)

[0036] In the formula, T0 is the time value obtained by counting N0 pulses, T a T is the time length between the arrival of the first pulse of the signal under test and the rising edge of the reference clock signal. b It is the time length between the rising edge of the second signal pulse to be measured and the rising edge of the reference clock signal;

[0037] S632, in T a During this period, the first constant current source C is used. s1 Charge capacitor C1;

[0038] S633, using a second constant current source C s2 With current I b =I a / m discharges the capacitor until the voltage drops below the reference voltage of the second comparator Comp2. This is deduced from the principle of equal charge during charging and discharging:

[0039]

[0040] In the formula, the magnitude of the charging current is I. a ;

[0041] S634. Using the first comparator Comp2, record the discharge time information and the comparator reference voltage V. ref2 Record data and output or save it to the timer.

[0042] This invention performs FMCW lidar signal processing based on the capacitor analog interpolation method. It utilizes the waveform broadening characteristic stored during the charging and discharging process of the capacitor, and then uses a high-precision reference clock for interpolation to obtain the intermediate frequency measurement of the signal.

[0043] In a more specific technical solution, S7 includes:

[0044] S71. Through capacitor C1, the time length T between the rising edge of the first pulse to be measured and the rising edge of the reference clock signal is set to high level. a The time length T between the rising edges of the second signal pulse to be measured and the reference clock signal. b By extending the time range, we obtain the first extended time range T′. a Second extended time range T′ b ;

[0045] S72, For the first extended time range T′ a Second extended time range T′ b Each is referenced by a clock signal f. s The pulse count is used to measure the time value T0; where the reference clock f is used. s The discharge time is timed, and the number of timing pulses N′ is obtained according to the following logic. a 、N′ b :

[0046]

[0047] S73. Calculate the period T based on the reference clock signal, and process it to obtain the intermediate frequency signal frequency value f. x .

[0048] In a more specific technical solution, S73, the period T is calculated using the following logic:

[0049]

[0050] This invention employs a capacitor-based analog interpolation method to implement FMCW lidar signal processing. By first converting the intermediate frequency signal into a square wave pulse signal, and then controlling the opening and closing of two switches through logic gate circuits composed of the signal under test and the reference clock signal respectively, the capacitor is rapidly charged and slowly discharged. This eliminates the ±1-digit counting error present in traditional pulse counting measurement methods, thereby accurately obtaining the period of the intermediate frequency signal under test and calculating its frequency. This provides an important prerequisite for the accurate calculation of the distance to the target.

[0051] In a more specific technical solution, an FMCW lidar signal processing system includes:

[0052] A laser is used to generate a laser signal; a first proportional coupler is used to divide and process the laser signal according to a first preset ratio to obtain a measurement optical signal and a first local oscillator optical signal, and the first proportional coupler is connected to the laser.

[0053] An optical modulator is used to input the measurement optical signal into the optical modulator. A signal generator generates a modulated sine wave sweep signal to modulate the measurement optical signal to obtain a modulated measurement optical signal. The optical modulator is connected to the first proportional coupler.

[0054] Erbium-doped fiber amplifier (EDFA) is used to amplify and process the modulated measurement optical signal to obtain the amplified measurement optical signal. The EDFA is connected to the optical modulator. Circulator and collimator are used to transmit the collimated measurement optical signal to the detection target and receive the reflected measurement optical signal. The EDFA is connected to the circulator and collimator.

[0055] The second proportional coupler is used to couple the reflected measurement light signal and the first local oscillator light signal according to the second preset ratio to obtain an energy-enhanced light signal, and input the energy-enhanced light signal to the balance detector. The second proportional coupler is connected to the circulator and the collimating lens. The balance detector is used to perform photoelectric signal conversion to obtain a converted electrical signal. The balance detector is connected to the second proportional coupler.

[0056] A transimpedance amplifier is used to amplify and process the converted electrical signal. The transimpedance amplifier is connected to a balanced detector. A signal generator is used to generate a second local oscillator signal. A mixer is used to perform electrical mixing operations on the converted electrical signal and the second local oscillator signal to obtain and output an intermediate frequency signal. The mixer is connected to the transimpedance amplifier.

[0057] A low-pass filter is used to perform low-pass filtering on the intermediate frequency signal to remove high-frequency mixing components from the intermediate frequency signal and obtain a low-pass filtered signal. The low-pass filter is connected to the mixer. A signal processing system is used to perform capacitor-based analog interpolation processing on the low-pass filtered signal. The signal processing system is connected to the low-pass filter. The signal processing system includes: a first high-speed comparator Comp1, a second high-speed comparator Comp2, AND gates, NOT gates, a first constant current source CS1, a second constant current source CS2, an integrating capacitor, and a timer.

[0058] The period of the low-pass filtered signal is measured, the intermediate frequency signal value is calculated based on the period, and the current time value T0 is obtained by counting N0 pulses within T0.

[0059] The present invention has the following advantages over the prior art:

[0060] This invention proposes a novel hardware architecture and intermediate frequency (IF) calculation method based on the traditional FMCW lidar pulse measurement method, combined with capacitance analog interpolation. This enables high-precision and high-efficiency FMCW lidar signal measurement. Therefore, the FCMW lidar signal processing method designed in this paper has significant advantages and application prospects in terms of architecture, cost, and detection accuracy. This invention achieves high-precision IF signal measurement of FMCW lidar through a simple architecture, offering advantages such as low cost and high resolution.

[0061] This invention employs a capacitor deployed after a transimpedance amplifier (TIA) and a high-speed comparator. After the comparator converts the intermediate frequency signal waveform into a square wave, the charging and discharging process of the capacitor is controlled by a logic circuit. A timer records the time information of the intermediate frequency signal. Then, the waveform information is broadened during the capacitor discharge process, and a high-precision counter is used to count the pulses within one cycle to finally measure the frequency of the waveform, thereby improving the accuracy of the distance information of the FMCW lidar.

[0062] This invention performs FMCW lidar signal processing based on the capacitor analog interpolation method. It utilizes the waveform broadening characteristic stored during the charging and discharging process of the capacitor, and then uses a high-precision reference clock for interpolation to obtain the intermediate frequency measurement of the signal.

[0063] This invention employs a capacitor-based analog interpolation method to implement FMCW lidar signal processing. By first converting the intermediate frequency signal into a square wave pulse signal, and then controlling the opening and closing of two switches through logic gate circuits composed of the signal under test and the reference clock signal respectively, the capacitor is rapidly charged and slowly discharged. This eliminates the ±1-digit counting error present in traditional pulse counting measurement methods, thereby accurately obtaining the period of the intermediate frequency signal under test and calculating its frequency. This provides an important prerequisite for the accurate calculation of the distance to the target.

[0064] This invention solves the technical problem in the prior art where a counting error of ±1 digit leads to low accuracy in calculating the period of the intermediate frequency signal under test and the distance to the target. Attached Figure Description

[0065] Figure 1 This is a schematic diagram of the basic steps of an FMCW lidar signal processing method according to Embodiment 1 of the present invention;

[0066] Figure 2 This is a block diagram of an FMCW lidar signal processing system according to Embodiment 1 of the present invention;

[0067] Figure 3 This is a hardware block diagram of the signal processing system in Embodiment 1 of the present invention;

[0068] Figure 4 This is a schematic diagram of frequency measurement based on capacitance analog interpolation method in Embodiment 1 of the present invention. Detailed Implementation

[0069] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0070] Example 1

[0071] like Figure 1 As shown, the FMCW lidar signal processing method provided by the present invention includes the following basic steps:

[0072] S1. The laser signal generated by the laser is divided into a measurement optical signal and a local oscillator optical signal using a 1:99 coupler;

[0073] In this embodiment, an FMCW lidar signal processing system includes: a laser 1, a 1:99 coupler 2, a signal generator 3, an optical modulator 4, a 50:50 coupler 5, a balanced detector 6, a transimpedance amplifier 7, an erbium-doped fiber amplifier 8, a circulator 9, a collimating lens 10, a mixer 11, a low-pass filter 12, and a signal processing system 13.

[0074] In this embodiment, the 1:99 coupler 2 is connected to the laser 1; the optical modulator 4 is connected to the 1:99 coupler 2; the erbium-doped fiber amplifier 8 is connected to the optical modulator 4; the erbium-doped fiber amplifier 8 is connected to the circulator 9 and the collimating lens 10; the 50:50 coupler 5 is connected to the circulator 9 and the collimating lens 10; the balanced detector 6 is connected to the 50:50 coupler 5; the transimpedance amplifier 7 is connected to the balanced detector 6; the signal generator 3 is connected to the optical modulator 4; the mixer 11 is linked to the transimpedance amplifier 7; the low-pass filter 12 is connected to the mixer 11; and the signal processing system 13 is connected to the low-pass filter 12.

[0075] In this embodiment, the 1:99 coupler 2 is defined as the measurement optical signal with 99% of its energy and the local oscillator optical signal with 1% of its energy.

[0076] In this embodiment, laser 1 first generates a laser signal, which then enters a 1:99 coupler 2. The 1:99 coupler 2 divides the energy emitted by laser 1 proportionally, with 99% of the energy light signal entering the optical modulator 4 as measurement light. In this embodiment, laser 1 includes, but is not limited to, various types of lasers such as DFB (Distributed Feedback Laser) laser 1 and VCSEL (Vertical-Cavity Surface-Emitting Laser) laser 1.

[0077] S2. Input the measurement optical signal into the optical modulator 4, and modulate it through the modulated sinusoidal sweep frequency signal generated by the signal generator 3;

[0078] like Figure 2 As shown, in this embodiment, the first part is the FMCW lidar signal generation section, see [link to documentation]. Figure 1 Laser 1 generates a laser signal, which is split into two beams by a 1:99 coupler 2 according to a certain energy ratio. One beam, accounting for 99% of the energy, is defined as the measurement optical signal, and the other beam, accounting for 1% of the energy, is defined as the local oscillator optical signal. The local oscillator optical signal, accounting for 1% of the energy, directly enters the first input port of the 50:50 coupler 5, while the measurement optical signal, accounting for 99% of the energy, directly enters the optical modulator 4. The optical modulator 4 requires an external bias voltage, specifically, the bias voltage range can be set to, for example, 0-5V.

[0079] S3. Amplify the modulated measurement optical signal and transmit it to the detection target through the circulator 9 and collimator 10, and receive the reflected measurement optical signal.

[0080] In this embodiment, the light signal amplified by the EDFA first enters the first port of the circulator 9 and is output from the second port, and enters the collimating lens 10. The collimating lens 10 collimates the light beam of the light signal and emits it onto the detection target. The light reflected back from the detection target enters the collimating lens 10 again and enters the second port of the circulator 9 again, and is output from the third port.

[0081] In this embodiment, a 1% energy optical signal is used as the local oscillator and enters the first input port of the 50:50 coupler 5. The optical modulator 4 requires an external bias voltage (typically 0-5V). Meanwhile, the signal generator 3 generates a sinusoidal sweep modulation wave, which is fed to both the optical modulator 4 and the mixer 11 in the back-end circuit. The signal output from the optical modulator 4 is further amplified by an EDFA (Erbium-doped fiber amplifier) ​​before entering the circulator 9. The circulator 9 is a three-port device. The optical signal amplified by the EDFA first enters the first port and then exits from the second port to the collimating lens 10. The collimating lens 10 collimates the optical signal beam to further prevent energy loss due to diffusion. The collimated beam then illuminates the target. The light reflected back from the target will then be received again by the collimating lens 10, enter from the second port of the circulator 9, and be output from the third port. The first and second ports, as well as the second and third ports, have excellent unidirectional laser transmission performance. The reverse transmission of the laser will exhibit high transmission loss, which can effectively protect the EDFA from the influence of the reverse transmitted laser.

[0082] S4. The received measurement optical signal and the local oscillator optical signal are coupled in a 50:50 coupler 5 to enhance the energy of the signal light, and then input into the balanced detector 6 for photoelectric signal conversion.

[0083] In this embodiment, the balanced detector 6 converts the input optical signal into an electrical signal while also eliminating the DC component and common-mode interference in the optical signal;

[0084] In this embodiment, the signal light output from port 3 of circulator 9 also enters port 2 of the previously mentioned 50:50 coupler 5 and couples with the 1% energy local oscillator signal light output from port 1 of 50:50 coupler 5 via 1:99 coupler 2, aiming to further enhance the total energy of the light. The signal output from 50:50 coupler 5 will enter the balanced detector 6 for photoelectric signal conversion. In addition, the balanced detector 6 will further suppress and eliminate common-mode noise in the signal.

[0085] S5. The converted electrical signal is amplified by the transimpedance amplifier 7 and electrically mixed with another local oscillator signal generated by the signal generator 3 in the mixer 11 to output the intermediate frequency signal.

[0086] In this embodiment, the intermediate frequency signal also contains high-frequency mixing components, so the intermediate frequency signal needs to be low-pass filtered.

[0087] In this embodiment, the current signal output by the balanced detector 6 is further amplified by the transimpedance amplifier 7, and the current signal is converted into a voltage signal. Then, the output signal of the transimpedance amplifier 7 enters the mixer 11 and is electrically mixed with another signal generated by the previous signal generator 3 to complete the process of outputting the intermediate frequency signal.

[0088] S6. Perform low-pass filtering on the intermediate frequency signal;

[0089] In this embodiment, the intermediate frequency (IF) signal output by mixer 11 still contains high-frequency components. Therefore, it is necessary to perform low-pass filtering on the IF signal to eliminate the high-frequency components. The signal after low-pass filtering then enters the signal processing system 13 for further signal processing using capacitance-based analog interpolation.

[0090] In this embodiment, the signal processing system 13 mainly consists of high-speed comparators Comp1 and Comp2, AND gates, NOT gates, constant current sources CS1 and CS2, integrating capacitors, and timers. The high-speed comparator Comp1 processes the input intermediate frequency signal f... x Perform pulse square wave conversion. Convert to an intermediate frequency signal f of a square wave. x The input is fed to the first port of the AND gate, while a reference clock signal of known frequency is fed to the second port of the AND gate through a NOT gate. The output of the AND gate then controls switches S1 and S2 respectively. When the AND gate output is 1, switch S1 closes and switch S2 opens. When the AND gate output is 0, switch S2 closes and switch S1 opens. First, when the AND gate output is 1, S1 closes and S2 opens, at which point the constant current source CS1 charges the integrating capacitor C1. Then, when the AND gate output is 0, S1 opens and S2 closes, at which point the constant current source CS2 slowly discharges the integrating capacitor C1. Comparator Comp2 modulates the discharge time using the comparator reference voltage V. ref2 Recording is performed and output to a timer for further recording. The timer operates on increments of f. s The timing function is completed using a reference frequency.

[0091] S7. The processed intermediate frequency signal is input into the signal processing system 13. The intermediate frequency signal is converted into a pulse square wave by a high-speed comparator. Then, the period of the intermediate frequency signal is accurately measured by performing capacitor analog interpolation with a reference clock signal of known frequency, and the frequency value of the intermediate frequency signal is calculated based on the period.

[0092] In this embodiment, the value of T0 is accurately obtained by counting N0 pulses within T0; specifically, T a T is the time length between the arrival of the first pulse of the signal under test and the rising edge of the reference clock signal. b It is the time length between the rising edge of the second signal pulse to be measured and the rising edge of the reference clock signal; through capacitor C1, T is respectively... a and T b Extend; by extending the time range T′ respectively. a and T′ b Each is passed through a reference clock signal f s Accurate time measurement is achieved by counting pulses; the period T is accurately calculated using the following formula (5), and f can be applied. x = 1 / T, thus obtaining the frequency value f of the intermediate frequency signal to be measured. x ;

[0093] In this embodiment, the high-speed comparator Comp1 in the signal processing system 13 converts the input intermediate frequency signal f x Perform pulse square wave conversion. Convert to an intermediate frequency signal f of a square wave. x The input is fed to the first port of the AND gate. Simultaneously, a reference clock signal of known frequency is fed to the second port of the AND gate through a NOT gate. The output of the AND gate then controls switches S1 and S2 respectively. When the AND gate output is 1, switch S1 is closed and switch S2 is open. When the AND gate output is 0, switch S2 is closed and switch S1 is open. First, when the AND gate output is 1, S1 is closed and S2 is open; at this time, the constant current source CS1 charges the integrating capacitor C1. Then, when the AND gate output is 0, S1 is open and S2 is closed; at this time, the constant current source CS2 slowly discharges the integrating capacitor C1. Comparator Comp2 will control the discharge time by interpolating it with the comparator reference voltage V. ref2 Recording and outputting data to a timer for further recording. The timer operates on an f-order basis. s The timing function is performed using a reference frequency. Overall, the value of T0 is accurately obtained by counting N0 pulses within T0. a and T b These are the time lengths between the arrival of the first test signal pulse at a high level and the rising edge of the reference clock signal, respectively, and the time length between the arrival of the second test signal pulse and the rising edge of the reference clock signal. Through capacitor C1, T is respectively... aand T b Expand the time frame. Then, expand the time frame by applying the expansion time range T′. a and T′ b Each is passed through a reference clock signal f s Accurate time measurement is achieved through pulse counting. Finally, the period T is precisely calculated using a formula, and f can be applied. x =1 / T to obtain the frequency value f of the intermediate frequency signal to be measured. x .

[0094] like Figure 3 As shown, in this embodiment, f x V is the intermediate frequency signal value after low-pass filtering in the previous step. ref The intermediate frequency signal f is the reference voltage value provided externally to the comparator (Comp). x After passing through the comparator, it is compared with the reference voltage, and a pulse square wave signal is output. Then C... s1 Connected to the comparator's output as a constant current source, when switch S1 is closed, the current source charges capacitor C1. The timer starts counting and records the current value T0. When the capacitor is fully charged, switch S1 opens and switch S2 closes. At this time, the counter records the current value T1, and capacitor C1 begins to discharge until it is fully discharged. The timer then records the current value T2 again, switch S2 opens, and switch S1 closes to prepare for the next capacitor charging and discharging process. s It is used as a reference clock input to the timer for timing.

[0095] like Figure 4 As shown, in this embodiment, the intermediate frequency signal is converted into a square wave pulse signal to be measured after passing through a high-speed comparator. x In the pulse to be measured f x The time T between the rising edge of the clock and the rising edge of the first reference clock thereafter a and the pulse to be measured f x The second pulse initiates the charging and discharging of the capacitor; see [link / reference]. Figure 4 The capacitance-based analog interpolation method requires measuring three time periods, namely T1 and T2. a And T b And T = NT s T s The period of the reference clock signal is used. The discharge and charging times of the capacitor are the extended time interval mT. a and mT b Then the time interval T to be determined is:

[0096] T = T0 + T a -T b (1)

[0097] Where T0 is obtained by counting N0 pulses, T a and T b These are the time lengths between the arrival of the first test signal pulse at a high level and the rising edge of the reference clock signal, and the time length between the arrival of the second test signal pulse and the rising edge of the reference clock signal. Since these are less than the period of one reference clock, they cannot be directly measured by counting the reference clock. Instead, they are extended using a capacitor-based analog interpolator based on the principle of capacitor charging and discharging. Then, the extended time ranges are measured using the reference clock f. s Perform pulse interpolation counting. This is done by measuring the reference clock f within the extended time range. s By determining the number of pulses, we can obtain the accurate value of the extended time range.

[0098] In T a During this period, a constant current source C was used. s1 The capacitor C1 is charged with a charging current of I. a After charging is complete, a constant current source C is used. s2 With a small current I b =I a The capacitor is discharged until it falls below the reference voltage of comparator Comp2. Based on the principle that the charge and discharge charges are equal, we can conclude that:

[0099]

[0100] After simplification, we can obtain T′ a =mT a This means that the capacitor's discharge time is m times the charging time, and then a reference clock f is used. s The discharge time is timed, and the number of timing pulses is N′. a Then we have:

[0101]

[0102] Similarly, for T b We can also obtain:

[0103]

[0104] The final time interval to be measured can be expressed by the following formula (5):

[0105]

[0106] In this embodiment, T can be obtained by using analog interpolation. a and T b The resolution of the measurement results over a time period is improved by a factor of m, while the reference clock f... sThe higher the frequency, the higher the accuracy of the final measured time interval T. Finally, after obtaining the period T of the measured frequency, f can be applied. x = 1 / T, thus obtaining the frequency value f of the intermediate frequency signal to be measured. x .

[0107] In summary, this invention proposes a novel hardware architecture and intermediate frequency (IF) calculation method based on the traditional FMCW lidar pulse measurement method, combined with capacitance analog interpolation. This enables high-precision and high-efficiency FMCW lidar signal measurement. Therefore, the FCMW lidar signal processing method designed in this paper has significant advantages and application prospects in terms of architecture, cost, and detection accuracy. This invention achieves high-precision IF signal measurement of FMCW lidar through a simple architecture, offering advantages such as low cost and high resolution.

[0108] This invention employs a capacitor deployed after a transimpedance amplifier (TIA) and a high-speed comparator. After the comparator converts the intermediate frequency signal waveform into a square wave, the charging and discharging process of the capacitor is controlled by a logic circuit. A timer records the time information of the intermediate frequency signal. Then, the waveform information is broadened during the capacitor discharge process, and a high-precision counter is used to count the pulses within one cycle to finally measure the frequency of the waveform, thereby improving the accuracy of the distance information of the FMCW lidar.

[0109] This invention performs FMCW lidar signal processing based on the capacitor analog interpolation method. It utilizes the waveform broadening characteristic stored during the charging and discharging process of the capacitor, and then uses a high-precision reference clock for interpolation to obtain the intermediate frequency measurement of the signal.

[0110] This invention employs a capacitor-based analog interpolation method to implement FMCW lidar signal processing. By first converting the intermediate frequency signal into a square wave pulse signal, and then controlling the opening and closing of two switches through logic gate circuits composed of the signal under test and the reference clock signal respectively, the capacitor is rapidly charged and slowly discharged. This eliminates the ±1-digit counting error present in traditional pulse counting measurement methods, thereby accurately obtaining the period of the intermediate frequency signal under test and calculating its frequency. This provides an important prerequisite for the accurate calculation of the distance to the target.

[0111] This invention solves the technical problem in the prior art where a counting error of ±1 digit leads to low accuracy in calculating the period of the intermediate frequency signal under test and the distance to the target.

[0112] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A signal processing method for FMCW lidar, characterized in that, The method includes: S1. A laser signal is generated using a laser, and the laser signal is divided and processed according to a first preset ratio through a first proportional coupler to obtain a measurement optical signal and a first local oscillator optical signal. S2. Input the measurement optical signal to the optical modulator, use the signal generator to generate a modulated sine wave sweep signal, and modulate the measurement optical signal to obtain a modulated measurement optical signal; S3. Amplify the modulated measurement optical signal to obtain an amplified measurement optical signal. Use a circulator and a collimating lens to transmit the collimated measurement optical signal to the detection target and receive the reflected measurement optical signal. S4. Using the second proportional coupler, the reflected measurement light signal and the first local oscillator light signal are coupled and processed according to the second preset ratio to obtain an energy-enhanced light signal. The energy-enhanced light signal is then input to the balanced detector for photoelectric signal conversion to obtain a converted electrical signal. S5. The converted electrical signal is amplified and processed using a transimpedance amplifier. The second local oscillator signal generated by the signal generator is used to perform electrical mixing operation on the converted electrical signal and the second local oscillator signal in a mixer to obtain and output an intermediate frequency signal. S6. The intermediate frequency signal is subjected to low-pass filtering to remove the high-frequency mixing components in the intermediate frequency signal, resulting in a low-pass filtered signal. The low-pass filtered signal is then subjected to capacitor-based analog interpolation using a signal processing system. The signal processing system includes: a first high-speed comparator Comp1, a second high-speed comparator Comp2, AND gates, NOT gates, a first constant current source CS1, a second constant current source CS2, an integrating capacitor C1, a timer, a first switch S1, and a second switch S2. The first high-speed comparator Comp1, the second high-speed comparator Comp2, and the AND gate are each provided with two input ports and one output port; the intermediate frequency signal f x and the first reference voltage signal V ref1 The signals are respectively input to the first port and the second port of the first high-speed comparator Comp1; using the first high-speed comparator Comp1, the intermediate frequency signal f is... x The pulse is square-waved to obtain a square-waved intermediate frequency (IF) signal; the output port of the first high-speed comparator Comp1 is connected to the first port of the AND gate, and the square-waved IF signal is input to the first port of the AND gate, so that the preset frequency reference clock signal f... s The signal is fed into the second port of the AND gate through a NOT gate to obtain the AND gate output signal, which is used to adjust the switching states of the first switch S1 and the second switch S2, which are connected in series. The first constant current source CS1 is connected to the first port of the first switch S1, and the second port of the second switch S2 is connected to the second constant current source CS2. The second port of the first switch S1 is also connected to the first input port of the integrating capacitor C1 and the second high-speed comparator Comp2. According to the switching state, the first constant current source CS1 and the second constant current source CS2 control the charging and discharging operation of the integrating capacitor C1. The output port of the second high-speed comparator Comp2 is connected to the first input port of the timer for pulse counting. S7. Measure the period of the low-pass filter signal, calculate the intermediate frequency signal value based on the period, and obtain the current time value T0 by performing a counting operation of N0 pulses within T0.

2. The FMCW lidar signal processing method according to claim 1, characterized in that, In S1, the laser includes a distributed feedback laser and a vertical cavity surface-emitting laser.

3. The FMCW lidar signal processing method according to claim 1, characterized in that, S2 includes: S21. The first local oscillator signal is brought into the first input port of the second proportional coupler; S22. The measurement optical signal is fed into the optical modulator, and an external bias voltage is supplied to the optical modulator. S23. A modulated sine wave sweep signal is generated using a signal generator, and the modulated sine wave sweep signal is given to the optical modulator and the back-end circuit mixer respectively.

4. The FMCW lidar signal processing method according to claim 1, characterized in that, S3 includes: S31. The modulated measurement optical signal is amplified and processed using an erbium-doped fiber amplifier (EDFA) to obtain the amplified measurement optical signal; S32. The measurement optical amplification signal is fed into the first port of the circulator, and the circulator output signal is output from the second port of the circulator. S33. The output signal of the circulator is fed into the collimating lens. The collimating lens is used to collimate the output signal of the circulator to obtain and transmit the collimated measurement light signal to the detection target. S34. The detected target reflects back the reflected measurement light signal, which enters the collimating lens, enters from the second port of the circulator, and exits from the third port of the circulator.

5. The FMCW lidar signal processing method according to claim 1, characterized in that, S4 includes: S41. Using the balanced detector, the energy-enhanced optical signal is converted into an electrical signal; S42. Using the balanced detector, perform DC component elimination and common-mode noise elimination operations on the energy-enhanced optical signal.

6. The FMCW lidar signal processing method according to claim 1, characterized in that, The step of controlling the charging and discharging operations of the first constant current source CS1 and the second constant current source CS2 on the integrating capacitor C1 according to the switching state includes: S631, based on the capacitor's discharge time mT a Charging time (mT) b The time interval T is obtained by using the following logic: T=T0+T a -T b (1) In the formula, T0 is the time value obtained by counting N0 pulses, T a T is the time length between the arrival of the first pulse of the signal under test and the rising edge of the reference clock signal. b It is the time length between the rising edge of the second signal pulse to be measured and the rising edge of the reference clock signal; S632, in T a During this period, the capacitor C1 is charged using the first constant current source CS1; S633, Using the second constant current source CS2 with current I b =I a / m discharges the capacitor until the voltage is lower than the reference voltage value of the second high-speed comparator Comp2, which is derived from the principle of equal charge and discharge: In the formula, the magnitude of the charging current is I. a , T′ a Indicates the first extended time range; S634. Using the second high-speed comparator Comp2, record the discharge time information and the comparator reference voltage V. ref2 It outputs and saves the data to the timer.

7. The FMCW lidar signal processing method according to claim 1, characterized in that, S7 includes: S71. Through capacitor C1, the time length T between the rising edge of the first pulse to be measured and the rising edge of the reference clock signal is set to high level. a The time length T between the rising edges of the second signal pulse to be measured and the reference clock signal. b By extending the time range, we obtain the first extended time range T′. a Second extended time range T′ b ; S72, regarding the first extended time range T′ a The second extended time range T′ b Each is referenced by a clock signal f. s The pulse count is used to measure the time value T0; wherein, the reference clock signal f is used. s The discharge time is timed, and the number of timing pulses N′ is obtained according to the following logic. a 、N′ b : S73. Calculate the period T based on the reference clock signal, and process it to obtain the intermediate frequency signal frequency value f. x .

8. The FMCW lidar signal processing method according to claim 7, characterized in that, In step S73, the period T is obtained using the following logic:

9. An FMCW lidar signal processing system, used to execute the FMCW lidar signal processing method according to any one of claims 1 to 8, characterized in that, The system includes: A laser for generating a laser signal; a first proportional coupler for dividing and processing the laser signal according to a first preset ratio to obtain a measurement optical signal and a first local oscillator optical signal, wherein the first proportional coupler is connected to the laser. An optical modulator is used to input the measurement optical signal into the optical modulator, and a modulated sine wave sweep signal is generated by a signal generator to modulate the measurement optical signal to obtain a modulated measurement optical signal. The optical modulator is connected to the first proportional coupler. An erbium-doped fiber amplifier (EDFA) is used to amplify and process the modulated measurement optical signal to obtain an amplified measurement optical signal. The EDFA is connected to the optical modulator. A circulator and a collimating lens are used to transmit the collimated measurement optical signal to the detection target and receive the reflected measurement optical signal. The EDFA is connected to the circulator and the collimating lens. The second proportional coupler is used to couple the reflected measurement light signal and the first local oscillator light signal according to the second preset ratio to obtain an energy-enhanced light signal, and input the energy-enhanced light signal to the balance detector. The second proportional coupler is connected to the circulator and the collimating lens. The balance detector is used to perform photoelectric signal conversion to obtain a converted electrical signal. The balance detector is connected to the second proportional coupler. A transimpedance amplifier is used to amplify and process the converted electrical signal, and the transimpedance amplifier is connected to the balanced detector; a signal generator is used to generate a second local oscillator signal; a mixer is used to perform electrical mixing operation on the converted electrical signal and the second local oscillator signal to obtain and output an intermediate frequency signal, and the mixer is connected to the transimpedance amplifier; A low-pass filter is used to perform low-pass filtering on the intermediate frequency signal to remove high-frequency mixing components from the intermediate frequency signal and obtain a low-pass filtered signal. The low-pass filter is connected to the mixer. A signal processing system is used to perform capacitor-based analog interpolation on the low-pass filtered signal. The signal processing system is connected to the low-pass filter. The signal processing system includes: a first high-speed comparator Comp1, a second high-speed comparator Comp2, AND gates, NOT gates, a first constant current source CS1, a second constant current source CS2, an integrating capacitor, and a timer. The period of the low-pass filtered signal is measured, the intermediate frequency signal value is calculated based on the period, and the current time value T0 is obtained by counting T0 pulses within T0.

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