Digital undersampling-based mixing pulse laser radar circuit and ranging method
By using a digital undersampling mixing pulse lidar circuit, which utilizes a global clock module and a pixel circuit module for undersampling mixing, the high complexity and high power consumption of existing lidar systems are solved, thus realizing a high-precision ranging and low-power lidar system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SUN YAT SEN UNIV
- Filing Date
- 2023-08-17
- Publication Date
- 2026-07-21
AI Technical Summary
Existing lidar systems use sinusoidal signal modulation, which results in high circuit complexity, high power consumption, and difficulty in achieving a measurement accuracy of 1 cm, especially in mass production where consistency is hard to guarantee.
A digital undersampling mixed-pulse lidar circuit is adopted. A high-frequency clock signal and a local oscillator signal are generated through a global clock module. Combined with the pixel circuit module, undersampling mixing is performed to reduce the design difficulty of the time measurement circuit and achieve higher accuracy ranging.
It achieves higher accuracy in ranging, reduces the design difficulty of time measurement circuits, and has low power consumption, making it suitable for large-scale integration and improving the stability and consistency of the system.
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Figure CN117192561B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of integrated circuit chip design technology, and in particular to a mixed-frequency pulse lidar circuit and ranging method based on digital undersampling. Background Technology
[0002] LiDAR ranging is a non-contact ranging method. Its ranging principle involves driving a laser diode (LD) to emit laser pulses to illuminate the target object, and using a photodiode (PD) to receive the reflected light signal. The system measures the time difference between laser emission and reflection, i.e., the time-of-flight (ToF), and combines this with the constant speed of light c to calculate the distance d between the system and the target object, i.e., d = 0.5c * ToF. From this formula, when d = 15 cm, the corresponding ToF = 1 nanosecond; when d = 1 cm, the corresponding ToF ≈ 66.7 picoseconds. Therefore, to achieve a measurement accuracy of 1 cm, traditional methods require a time measurement accuracy of 66.7 picoseconds, which presents a significant design challenge for existing mature chips. Existing LiDAR systems use sinusoidal signal modulation of the laser signal, and frequency mixing schemes have been proposed to reduce system design complexity. However, this method uses sinusoidal signals for laser modulation, resulting in high circuit and system complexity and high system power consumption. In addition, this method requires mixing two sinusoidal signals with a certain frequency difference. The required high-fidelity mixing circuit design is complex, consumes a lot of power, and is difficult to ensure consistency during mass production, thus resulting in high design and manufacturing costs. Summary of the Invention
[0003] To address the aforementioned technical problems, the present invention aims to provide a mixed-frequency pulsed lidar circuit and ranging method based on digital undersampling, which can achieve higher precision measurement and reduce the design difficulty of time measurement circuits by amplifying the flight time of pulsed laser signals.
[0004] The first technical solution adopted in this invention is: a mixed-frequency pulse lidar circuit based on digital undersampling, comprising a laser driving circuit module, a laser diode module, a pixel circuit module, and a global clock module. The output terminal of the laser diode module outputs a laser pulse signal, the input terminal of the laser diode module is connected to the output terminal of the laser driving circuit module, the input terminal of the laser driving circuit module is connected to the output terminal of the global clock module, the output terminal of the global clock module is connected to the input terminal of the pixel circuit module, and the output terminal of the pixel circuit module outputs ranging information, wherein:
[0005] The laser driving circuit module is used to receive driving signals and amplify them.
[0006] The laser diode module is used to receive the amplified driving signal, perform conversion processing, generate a laser pulse signal, and emit it to the target object.
[0007] The global clock module is used to generate high-frequency clock signals and local oscillator signals;
[0008] The pixel circuit module is used to receive the reflected signal reflected by the target object, the high-frequency clock signal and the local oscillator signal, and perform undersampling mixing processing to output the distance information between the target object and the laser diode module.
[0009] Furthermore, the global clock module also includes a 64x frequency multiplier phase-locked loop module and a 63x frequency divider module, which are electrically connected.
[0010] The 64-fold frequency-locked loop module is used to acquire the drive signal and use it as a reference clock for generating the high-frequency clock signal;
[0011] The 64-fold frequency-locked loop module is used to generate the high-frequency clock signal and transmit it to the pixel circuit module;
[0012] The 63-fold frequency divider module is used to generate the local oscillator signal and transmit it to the pixel circuit module.
[0013] Furthermore, the pixel circuit module also includes a photodiode module, a clamping protection circuit module, a first D flip-flop module, a second D flip-flop module, a 16-bit counter module, a 16-bit shift register module, and a serial peripheral interface controller module. The photodiode module is connected to the clamping protection circuit module, the clamping protection circuit module is connected to the second D flip-flop module, the second D flip-flop module is connected to the first D flip-flop module, the first D flip-flop module and the second D flip-flop module are connected to the 16-bit counter module, the 16-bit counter module is connected to the 16-bit shift register module, and the 16-bit shift register module is connected to the serial peripheral interface controller module, wherein:
[0014] The photodiode module is used to receive the reflected signal from the target object and perform photoelectric conversion processing to generate a receiving pulse signal;
[0015] The clamping protection circuit module is used to fix the received pulse signal within a preset threshold range and generate a filtered received pulse signal.
[0016] The first D flip-flop module is used to receive the local oscillator signal and the drive signal, perform undersampling processing, and output the sampled transmit pulse signal;
[0017] The second D flip-flop module is used to receive the local oscillator signal and the filtered received pulse signal, perform undersampling processing, and output the sampled received pulse signal;
[0018] The 16-bit counter module is used to receive the high-frequency clock signal, the sampled transmitted pulse signal and the sampled received pulse signal, and to perform time measurement, and output the distance information between the target object and the laser diode module.
[0019] The 16-bit shift register module is used to store distance information between the target object and the laser diode module;
[0020] The serial peripheral interface controller module is used to receive and transmit the distance information between the target object and the laser diode module.
[0021] Meanwhile, the present invention also provides a ranging method based on a digital undersampling mixing pulse lidar circuit, specifically including the following steps:
[0022] The laser driving circuit module transmits the driving signal to the laser diode module;
[0023] The laser diode module receives the driving signal and generates the laser pulse signal, which is then emitted to the target.
[0024] The target object receives the laser pulse signal and generates a reflected signal;
[0025] The global clock module generates the high-frequency clock signal and the local oscillator signal;
[0026] The pixel circuit module receives the reflected signal, the high-frequency clock signal, and the local oscillator signal from the target object, performs undersampling mixing, and outputs the distance information between the target object and the laser diode module.
[0027] Furthermore, the step of the pixel circuit module receiving the reflected signal from the target object, the high-frequency clock signal, and the local oscillator signal, performing undersampling mixing processing, and outputting the distance information between the target object and the laser diode module specifically includes:
[0028] The photodiode receives the reflected signal from the target object and performs photoelectric conversion processing to output a received pulse signal.
[0029] The clamping protection circuit module filters the received pulse signal to obtain a filtered received pulse signal.
[0030] Based on the first D flip-flop module, the local oscillator signal and the driving signal are subjected to undersampling mixing to obtain the sampled transmit pulse signal;
[0031] Based on the second D flip-flop module, the local oscillator signal and the filtered received pulse signal are subjected to undersampling mixing to obtain the sampled received pulse signal.
[0032] Based on the 16-bit counter module, combined with the high-frequency clock signal, the sampled transmit pulse signal, and the sampled receive pulse signal, the distance information between the target object and the laser diode module is output.
[0033] Furthermore, the undersampling mixing process specifically includes:
[0034] The laser pulse signal is input to the clock input port of the first D flip-flop module, the local oscillator signal is input to the D input port of the first D flip-flop module, the local oscillator signal and the driving signal are subjected to undersampling aliasing processing, and the Q output port of the first D flip-flop module outputs the sampled emission pulse signal.
[0035] The filtered received pulse signal is input to the clock input port of the second D flip-flop module, and the local oscillator signal is input to the D input port of the second D flip-flop module. The local oscillator signal and the filtered received pulse signal are subjected to undersampling aliasing processing, and the sampled received pulse signal is output from the Q output port of the second D flip-flop module.
[0036] Furthermore, the step of outputting distance information data between the target object and the laser diode module based on the 16-bit counter module, combined with the high-frequency clock signal, the sampled transmitted pulse signal, and the sampled received pulse signal, specifically includes:
[0037] The phase difference is calculated based on the sampled transmitted pulse signal and the sampled received pulse signal;
[0038] The rising edge time interval between the sampled transmitted pulse signal and the sampled received pulse signal is calculated based on the phase difference value;
[0039] Based on the phase difference and the rising edge time interval, the distance information between the target object and the laser diode module is calculated using the distance calculation formula.
[0040] Furthermore, the specific expression for calculating the phase difference is as follows:
[0041] ΔΦ=2π*ToF*f1
[0042] In the above formula, ΔΦ represents the phase difference between the sampled transmitted pulse signal and the sampled received pulse signal, ToF represents the time difference between the laser pulse signal and the received pulse signal, and f1 represents the frequency of the driving signal.
[0043] Furthermore, the specific expression for calculating the rising edge time interval between the sampled transmitted pulse signal and the sampled received pulse signal based on the phase difference value is as follows:
[0044]
[0045] In the above formula, t represents the rising edge time interval between the sampled transmitted pulse signal and the sampled received pulse signal, and f2 represents the period of the local oscillator signal.
[0046] Furthermore, the specific expression of the distance calculation formula is as follows:
[0047] d = 0.5c * ToF
[0048] In the above formula, d represents the distance information between the target object and the laser diode module, and c represents the speed of light.
[0049] The beneficial effects of the circuit and method of the present invention are as follows: The present invention drives the laser diode module to emit a laser pulse signal and emits it to the target object through the laser driving circuit module. The target object obtains the laser pulse signal and reflects the corresponding signal to the pixel circuit module. The global clock module generates a local oscillator signal and transmits it to the pixel circuit module. The pixel circuit module mixes and samples the laser pulse signal and the reflected received signal with the local oscillator signal respectively, and amplifies the laser pulse signal and the reflected received signal. As a result, the laser flight time of the pulse signal is amplified. After the amplification through the undersampling process, the measurement accuracy of 1 cm is also achieved. The accuracy required to measure the time interval t is reduced, which further reduces the design difficulty of the time measurement circuit. Attached Figure Description
[0050] Figure 1 This is a schematic diagram of the structure of a mixing pulse lidar circuit based on digital undersampling according to an embodiment of the present invention;
[0051] Figure 2 This is a flowchart illustrating the steps of the ranging method based on a digital undersampling mixed-frequency pulse lidar circuit according to an embodiment of the present invention.
[0052] Figure 3 This is a schematic diagram illustrating the principle of time interval measurement based on a D flip-flop in an embodiment of the present invention;
[0053] Figure 4This is a schematic diagram illustrating the data flow principle between the transmitted pulse signal and the received pulse signal in an embodiment of the present invention;
[0054] Figure 5 This is a schematic diagram illustrating the principle of measuring the time interval between a 400kHz laser pulse signal and a 400kHz received pulse signal according to an embodiment of the present invention.
[0055] Figure 6 This is a schematic diagram of the signal transmission structure of the mixed-frequency pulse lidar circuit according to an embodiment of the present invention. Detailed Implementation
[0056] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The step numbers in the following embodiments are only for ease of explanation and do not limit the order of the steps. The execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.
[0057] The basic principle of the digital undersampling mixed-frequency pulse lidar circuit system of this invention is to emit a light pulse signal (transmitted signal) to the target object. The light is reflected from the object's surface and absorbed by a photodiode in the system, generating an electrical signal (received signal) which is then received by the system. The time measurement circuit in the system measures the time interval between the transmitted and received signals, and combines this with the speed of light in air. By calculating d = 0.5c * ToF, the distance between the target object and the system can be obtained. Figure 4 A pixel consists of one transmitting signal, one photodiode, one time measurement circuit, and one serial peripheral interface (slave). Measurement data is sent out through the serial peripheral interface. Each pixel and the host are connected in a daisy-chain topology as shown in the figure. After the serial peripheral interface (host) collects the data of each pixel, it is transmitted to the distance information processing (host computer) through the on-chip parallel bus.
[0058] Reference Figure 1 This invention provides a mixed-frequency pulse lidar circuit based on digital undersampling, including a laser driving circuit module, a laser diode module, a pixel circuit module, and a global clock module. The output terminal of the laser diode module outputs a laser pulse signal. The input terminal of the laser diode module is connected to the output terminal of the laser driving circuit module. The input terminal of the laser driving circuit module is connected to the output terminal of the global clock module. The output terminal of the global clock module is connected to the input terminal of the pixel circuit module. The output terminal of the pixel circuit module outputs ranging information.
[0059] The laser drive circuit module is used to receive and amplify the 25MHz drive signal;
[0060] The laser diode module is used to receive the amplified 25MHz drive signal, perform conversion processing, generate a 25MHz laser pulse signal, and emit it to the target.
[0061] The global clock module is used to generate a 1.6GHz high-frequency clock signal and a 25.4MHz local oscillator signal;
[0062] Specifically, the global clock module also includes a 64x frequency multiplier phase-locked loop module and a 63x frequency divider module. The 64x frequency multiplier phase-locked loop module and the 63x frequency divider module are electrically connected. The 64x frequency multiplier phase-locked loop module is used to acquire a 25MHz drive signal and use it as a reference clock to generate a high-frequency clock signal. The 64x frequency multiplier phase-locked loop module is used to generate a 1.6GHz high-frequency clock signal and transmit it to the pixel circuit module. The 63x frequency divider module is used to generate a 25.4MHz local oscillator signal and transmit it to the pixel circuit module.
[0063] The pixel circuit module is used to receive the reflected signal from the target object, the 1.6GHz high-frequency clock signal and the 25.4MHz local oscillator signal, and perform undersampling mixing processing to output the distance information between the target object and the laser diode module.
[0064] Specifically, the pixel circuit module also includes a photodiode module, a clamping protection circuit module, a first D flip-flop module, a second D flip-flop module, a 16-bit counter module, a 16-bit shift register module, and a serial peripheral interface controller module. The photodiode module is connected to the clamping protection circuit module, which is in turn connected to the second D flip-flop module. The second D flip-flop module is connected to the first D flip-flop module, and both the first and second D flip-flop modules are connected to the 16-bit counter module. The 16-bit counter module is connected to the 16-bit shift register module, which is also connected to the serial peripheral interface controller module. The photodiode module is used to process the reflected signal from the target object through photoelectric conversion, generating a received pulse signal. The clamping protection circuit module is used to fix the received pulse signal within a preset threshold range, generating a filtered received pulse signal. The system consists of three modules: a receiving pulse signal module and a receiving pulse signal module. The first D flip-flop module receives the 25.4MHz local oscillator signal and the 25MHz drive signal, performs undersampling processing, and outputs a sampled 400kHz transmit pulse signal. The second D flip-flop module receives the 25.4MHz local oscillator signal and the filtered receive pulse signal, performs undersampling processing, and outputs a sampled 400kHz receive pulse signal. The 16-bit counter module receives the 1.6GHz high-frequency clock signal, the sampled 400kHz transmit pulse signal, and the sampled 400kHz receive pulse signal, performs time measurement, and outputs the distance information between the target object and the laser diode module. The 16-bit shift register module stores the distance information between the target object and the laser diode module. The serial peripheral interface controller module receives and displays the distance information between the target object and the laser diode module.
[0065] Reference Figure 2 and Figure 6 The ranging method based on a digital undersampling mixed-frequency pulse lidar circuit includes the following steps:
[0066] S1. The laser drive circuit module transmits a drive signal to the laser diode module;
[0067] S2. The laser diode module receives the drive signal and generates a laser pulse signal, which is then emitted to the target object.
[0068] Specifically, unlike traditional sinusoidal optical signal modulation, the transmitted signal in this invention still employs traditional pulse modulation. The rise and fall times of the transmitted signal pulse are both 1 nanosecond, the full width at half maximum (FWHM) of the pulse is 3 nanoseconds, and the pulse repetition frequency is 25MHz. The received signal is obtained through reflection from an object, and its shape is consistent with the transmitted signal; therefore, the electrical signal obtained after conversion by a photodiode is also consistent. Due to the high speed of light, the actual flight time is very short. According to the distance calculation formula d = 0.5c * ToF, a time measurement circuit with a resolution of 67 picoseconds is required to achieve a measurement accuracy of 1 centimeter. Therefore, this system introduces a D flip-flop undersampling technique, mixing the transmitted and received signals with a 25.4MHz local oscillator signal respectively to obtain the transmitted sample signal and the received sample signal.
[0069] S3. The target object receives the laser pulse signal and generates a reflected signal;
[0070] S4. The photodiode receives the reflected signal from the target object and performs photoelectric conversion processing, outputting a received pulse signal;
[0071] S5. The received pulse signal is filtered by the clamping protection circuit module to obtain the filtered received pulse signal.
[0072] S6. Generate high-frequency clock signals and local oscillator signals through the global clock module;
[0073] S7. Based on the first D flip-flop module, the local oscillator signal and the drive signal are undersampled and mixed to obtain the sampled transmit pulse signal.
[0074] S8. Based on the second D flip-flop module, the local oscillator signal and the filtered received pulse signal are undersampled and mixed to obtain the sampled received pulse signal.
[0075] Specifically, a 25MHz drive signal is input to the clock input port of the first D flip-flop module, and a 25.4MHz local oscillator signal is input to the D input port of the first D flip-flop module. Undersampling aliasing processing is performed on the 25.4MHz local oscillator signal and the 25MHz laser pulse signal. The Q output port of the first D flip-flop module outputs a sampled 400kHz transmit pulse signal. The filtered receive pulse signal is input to the clock input port of the second D flip-flop module, and a 25.4MHz local oscillator signal is input to the D input port of the second D flip-flop module. Undersampling aliasing processing is performed on the 25.4MHz local oscillator signal and the filtered receive pulse signal. The Q output port of the second D flip-flop module outputs a sampled 400kHz receive pulse signal.
[0076] Furthermore, mixing and sampling share the same mathematical essence, especially when one of the signals used for mixing is a pulse train with a fixed frequency (often called the repetition frequency), in which case they exhibit identical time-domain characteristics. In lidar ranging applications, optical signals can be modulated using pulse signals with a full width at half maximum (FWHM) of approximately 3 nanoseconds, conforming to the pulse train sampling model mentioned earlier. In addition to sinusoidal signals, any other form of periodic signal with a fixed frequency (often called the local oscillator frequency) can also be sampled (or mixed), such as square wave signals, which are readily available in digital circuit systems.
[0077] The mixing process of this invention can be completed using only two D flip-flops. For example... Figure 5 As shown, the 25.4MHz local oscillator signal is connected to the D input ports of two D flip-flops, and the 25MHz transmit and receive signals are connected to the clock input ports of the two D flip-flops respectively. This connection method determines that the 25MHz transmit and receive signals sample the 25.4MHz local oscillator signal separately. According to the principle that undersampling will cause aliasing, the frequencies obtained after sampling are all 400kHz, and the phase information is still retained in the undersampled 400kHz signal.
[0078] In this embodiment, the formula for calculating the phase difference between the sampled transmitted pulse signal and the sampled received pulse signal is as follows:
[0079] ΔΦ=2π*ToF*f1
[0080] In the above formula, ΔΦ represents the phase difference between the sampled transmitted pulse signal and the sampled received pulse signal, ToF represents the time difference between the laser pulse signal and the received pulse signal, and f1 represents the frequency of the driving signal.
[0081] The specific expression for calculating the rising edge time interval between the sampled transmitted pulse signal and the sampled received pulse signal based on the phase difference is as follows:
[0082]
[0083] In the above formula, t represents the rising edge time interval between the sampled transmitted pulse signal and the sampled received pulse signal after the bit difference value is calculated, and f2 represents the period of the local oscillator signal;
[0084] Furthermore, assuming the distance between the target and the system is d, the time of flight of the laser is ToF, and the speed of light is c (approximately 300,000 km / s), then the time difference between the 25MHz transmitted pulse and the received pulse is:
[0085] d = 0.5c * ToF
[0086] In the above formula, d represents the distance information between the target object and the laser diode module, and c represents the speed of light;
[0087] The corresponding phase difference can then be calculated:
[0088] ΔΦ = 2π * ToF / 40ns
[0089] In the above formula, ΔΦ represents the phase difference between the sampled 400kHz transmitted pulse signal and the sampled 400kHz received pulse signal, ToF represents the time difference between the 25MHz laser pulse signal and the received pulse signal, and ns represents 40 nanoseconds.
[0090] Due to the phase-preserving property of undersampling aliasing, the phase difference between the 400kHz transmitted and received pulses remains ΔΦ. However, because the frequency decreases and the pulse period lengthens, the time difference between the 400kHz transmitted and received pulses is now:
[0091] t=2500ns*ΔΦ / 2π=62.5*ToF
[0092] In the above formula, t represents the rising edge time interval between the sampled 400kHz laser pulse signal and the sampled 400kHz received pulse signal, calculated by the position difference value.
[0093] Therefore, it can be seen that Time-of-Flight (ToF) is magnified by 62.5 times on the time scale, and the measurement of time interval t is easier than direct measurement of ToF. As mentioned earlier, for a distance accuracy of 1 cm, the required ToF measurement resolution is 66.7 picoseconds. After the undersampling process, the same measurement accuracy of 1 cm can be achieved. The accuracy required to measure the time interval t is 66.7 picoseconds * 62.5 = 4.17 nanoseconds, which greatly reduces the design difficulty of the time measurement circuit.
[0094] Furthermore, traditional phase-detection LiDAR circuits use sinusoidal signals to modulate optical signals, resulting in significant power consumption overhead from LEDs and analog mixers (typically implemented using Gilbert cells). The mixers and filters also have large areas, making them unsuitable for large-scale, array-based integration. Moreover, their stability is greatly affected by power supply voltage, temperature, and chip manufacturing process variations, making it difficult to guarantee consistent pixel performance during array integration. In contrast, the digital mixer in this invention is implemented using only two basic digital circuit units (D latches). Designed and simulated using a 180nm chip process, its power consumption is only 15 microwatts, and its area is only 100 square micrometers. Therefore, the digital undersampling mixing technology in this system combines the advantages of high resolution, low power consumption, and high area efficiency.
[0095] S9, based on a 16-bit counter module, combines a high-frequency clock signal, a sampled transmit pulse signal, and a sampled receive pulse signal to output distance information between the target object and the laser diode module.
[0096] Specifically, the phase difference between the sampled 400kHz laser pulse signal and the sampled 400kHz received pulse signal is obtained; the rising edge time interval between the sampled 400kHz laser pulse signal and the sampled 400kHz received pulse signal is calculated based on the phase difference and the rising edge time interval; and the distance information between the target object and the laser diode module is obtained by calculating the distance using the distance calculation formula.
[0097] In summary, the ranging method of this invention uses a pulse signal to modulate and drive a laser diode, generating a pulse signal with a half-width of approximately 3 nanoseconds and a repetition frequency of 25 MHz to illuminate the target. The reflected light signal received by the photodiode is also a pulse signal with a half-width of approximately 3 nanoseconds and a repetition frequency of 25 MHz. The time difference between the two pulses is the laser time of flight (ToF). By sampling the same 25.4 MHz square wave local oscillator signal from the transmitted and received pulse trains, a 400 kHz signal and a 50.4 MHz signal can be obtained according to the principle of frequency mixing. Due to the characteristics of the D flip-flop circuit in the digital circuit, the 50.4 MHz signal is completely eliminated. At this time, the output signal only contains the 400 kHz signal. Since the pulse repetition frequency is very close to the frequency of the local oscillator signal, the 400 kHz signal is essentially generated through aliasing. Therefore, this sampling process is an undersampling process.
[0098] The laser emits and illuminates the target object. The corresponding reflected signal is received by the photodiode and generates a 25MHz receiving pulse. The emitted pulse and the receiving pulse are respectively sampled by a D flip-flop to sample the 25.4MHz local oscillator signal, and correspondingly, emitted pulse and receiving pulse with a frequency of 400kHz are generated. By measuring the time interval between the rising edges of the 400kHz emitted pulse and the receiving pulse, the distance information between the target object and the system can be obtained.
[0099] Both sampling and undersampling have the characteristic of phase invariance, meaning the phase information of the pulse train is retained in the sampled 400kHz signal. However, due to the decrease in signal frequency after mixing, the time reflected by the same phase difference is amplified. For example, assuming the target object is 60 cm away from the system and the system measures a flight time of 4 nanoseconds, for a pulse train with a repetition frequency of 25 MHz, its period is 40 nanoseconds, and therefore its corresponding phase difference is 2π*4 / 40 = π / 5. When this pulse train undersamples the 25.4 MHz local oscillator signal, the π / 5 phase information is still retained, while the signal period becomes 2500 nanoseconds. Therefore, the measurement time required after mixing is 2500*(π / 5) / 2π = 250 nanoseconds. It is evident that a duration of 250 nanoseconds is easier to measure than directly obtained flight time. It is not difficult to conclude that to achieve a measurement accuracy of 1 centimeter, the time measurement accuracy needs to reach 250 nanoseconds / 60 centimeters = 4.17 nanoseconds. This accuracy is not difficult to achieve with common 180-nanometer processes. This invention amplifies the laser pulse signal and the reflected reception signal, increasing the laser flight time of the pulse signal by 62.5 times. Compared to the existing technology requiring a ToF measurement resolution of 66.7 picoseconds for a distance accuracy of 1 centimeter, this invention, through undersampling amplification, also achieves a measurement accuracy of 1 centimeter. The accuracy required to measure the time interval t is 66.7 picoseconds * 62.5 = 4.17 nanoseconds, further reducing the design difficulty of the time measurement circuit.
[0100] The content of the above method embodiments is applicable to this system embodiment. The specific functions implemented in this system embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.
[0101] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.
Claims
1. A mixing pulse lidar circuit based on digital undersampling, characterized in that, The system includes a laser driving circuit module, a laser diode module, a pixel circuit module, and a global clock module. The laser diode module outputs a laser pulse signal. The input of the laser diode module is connected to the output of the laser driving circuit module. The input of the laser driving circuit module is connected to the output of the global clock module. The output of the global clock module is connected to the input of the pixel circuit module. The pixel circuit module outputs ranging information. The laser driving circuit module is used to receive driving signals and amplify them. The laser diode module is used to receive the amplified driving signal, perform conversion processing, generate a laser pulse signal, and emit it to the target object. The global clock module is used to generate high-frequency clock signals and local oscillator signals; The pixel circuit module is used to receive the reflected signal reflected by the target object, the high-frequency clock signal and the local oscillator signal, and perform undersampling mixing processing to output the distance information between the target object and the laser diode module; The pixel circuit module includes a photodiode module, a clamping protection circuit module, a first D flip-flop module, a second D flip-flop module, a 16-bit counter module, a 16-bit shift register module, and a serial peripheral interface controller module. The photodiode module is connected to the clamping protection circuit module, which is also connected to the second D flip-flop module. The second D flip-flop module is connected to the first D flip-flop module. The first and second D flip-flop modules are connected to the 16-bit counter module, which is connected to the 16-bit shift register module. The 16-bit shift register module is connected to the serial peripheral interface controller module. The photodiode module is used to receive the reflected signal from the target object and perform photoelectric conversion processing to generate a receiving pulse signal; The clamping protection circuit module is used to fix the received pulse signal within a preset threshold range and generate a filtered received pulse signal. The first D flip-flop module is used to receive the local oscillator signal and the drive signal, perform undersampling processing, and output the sampled transmit pulse signal; The second D flip-flop module is used to receive the local oscillator signal and the filtered received pulse signal, perform undersampling processing, and output the sampled received pulse signal; The 16-bit counter module is used to receive the high-frequency clock signal, the sampled transmitted pulse signal and the sampled received pulse signal, and to perform time measurement, and output the distance information between the target object and the laser diode module. The 16-bit shift register module is used to store distance information between the target object and the laser diode module; The serial peripheral interface controller module is used to receive and transmit the distance information between the target object and the laser diode module.
2. The mixing pulse lidar circuit based on digital undersampling according to claim 1, characterized in that, The global clock module further includes a 64x frequency multiplier phase-locked loop module and a 63x frequency divider module, which are electrically connected. The 64-fold frequency-locked loop module is used to acquire the drive signal and use it as a reference clock for generating the high-frequency clock signal; The 64-fold frequency-locked loop module is used to generate the high-frequency clock signal and transmit it to the pixel circuit module; The 63-fold frequency divider module is used to generate the local oscillator signal and transmit it to the pixel circuit module.
3. A ranging method for a mixing pulse lidar circuit based on digital undersampling as described in any one of claims 1-2, characterized in that, Includes the following steps: The laser driving circuit module transmits the driving signal to the laser diode module; The laser diode module receives the driving signal and generates the laser pulse signal, which is then emitted to the target. The target object receives the laser pulse signal and generates a reflected signal; The global clock module generates the high-frequency clock signal and the local oscillator signal; The pixel circuit module receives the reflected signal, the high-frequency clock signal, and the local oscillator signal from the target object, performs undersampling mixing, and outputs the distance information between the target object and the laser diode module.
4. The ranging method of the mixing pulse lidar circuit based on digital undersampling according to claim 3, characterized in that, The step of the pixel circuit module receiving the reflected signal from the target object, the high-frequency clock signal, and the local oscillator signal, performing undersampling mixing, and outputting the distance information between the target object and the laser diode module specifically includes: The photodiode receives the reflected signal from the target object and performs photoelectric conversion processing to output a received pulse signal. The clamping protection circuit module filters the received pulse signal to obtain a filtered received pulse signal. Based on the first D flip-flop module, the local oscillator signal and the driving signal are subjected to undersampling mixing to obtain the sampled transmit pulse signal; Based on the second D flip-flop module, the local oscillator signal and the filtered received pulse signal are subjected to undersampling mixing to obtain the sampled received pulse signal. Based on the 16-bit counter module, combined with the high-frequency clock signal, the sampled transmit pulse signal, and the sampled receive pulse signal, the distance information between the target object and the laser diode module is output.
5. The ranging method based on digital undersampling mixed-frequency pulse lidar circuit according to claim 4, characterized in that, The undersampling mixing process specifically includes: The laser pulse signal is input to the clock input port of the first D flip-flop module, the local oscillator signal is input to the D input port of the first D flip-flop module, the local oscillator signal and the driving signal are subjected to undersampling aliasing processing, and the Q output port of the first D flip-flop module outputs the sampled emission pulse signal. The filtered received pulse signal is input to the clock input port of the second D flip-flop module, and the local oscillator signal is input to the D input port of the second D flip-flop module. The local oscillator signal and the filtered received pulse signal are subjected to undersampling aliasing processing, and the sampled received pulse signal is output from the Q output port of the second D flip-flop module.
6. The ranging method of the mixed-frequency pulse lidar circuit based on digital undersampling according to claim 4, characterized in that, The step of outputting distance information between the target object and the laser diode module based on the 16-bit counter module, combined with the high-frequency clock signal, the sampled transmitted pulse signal, and the sampled received pulse signal, specifically includes: The phase difference value is calculated based on the sampled transmitted pulse signal and the sampled received pulse signal; The rising edge time interval between the sampled transmitted pulse signal and the sampled received pulse signal is calculated based on the phase difference value; Based on the phase difference and the rising edge time interval, the distance information between the target object and the laser diode module is calculated using the distance calculation formula.
7. The ranging method based on digital undersampling mixed-frequency pulse lidar circuit according to claim 6, characterized in that, The specific expression for calculating the phase difference is as follows: In the above formula, This represents the phase difference between the sampled transmitted pulse signal and the sampled received pulse signal. This indicates the time difference between the laser pulse signal and the received pulse signal. This indicates the frequency of the driving signal.
8. The ranging method of the mixed-frequency pulse lidar circuit based on digital undersampling according to claim 6, characterized in that, The specific expression for calculating the rising edge time interval between the sampled transmitted pulse signal and the sampled received pulse signal based on the phase difference is as follows: In the above formula, The bit difference value indicates that the rising edge time interval between the sampled transmitted pulse signal and the sampled received pulse signal is calculated. This indicates the period of the local oscillator signal.
9. The ranging method of the mixed-frequency pulse lidar circuit based on digital undersampling according to claim 6, characterized in that, The specific expression for the distance calculation formula is as follows: In the above formula, This represents the distance information between the target object and the laser diode module. It represents the speed of light.