CN115372943A

CN115372943A - FMCW laser radar system for eliminating direct current quantity and control method

Info

Publication number: CN115372943A
Application number: CN202211052941.0A
Authority: CN
Inventors: 赵毅强; 郑肖肖; 谢继勇; 李尧; 叶茂
Original assignee: Anhui Zhuozhan Electronic Technology Co ltd; Hefei Institute Of Innovation And Development Tianjin University
Current assignee: Anhui Zhuozhan Electronic Technology Co ltd; Hefei Institute Of Innovation And Development Tianjin University
Priority date: 2022-08-31
Filing date: 2022-08-31
Publication date: 2022-11-22

Abstract

The invention discloses an FMCW laser radar system and a control method aiming at direct current elimination.A system optical and detector module comprises a detector array, a signal amplification and conversion module comprises an analog amplification array, a differential to single-ended array, a multiplexer and a variable gain amplifier, a data processing module comprises an analog-to-digital converter and an FPGA, and the analog amplification array adopts a differential structure; the output of the detector array is connected with the differential-to-single-ended array through the analog amplification array, and the output of the differential-to-single-ended array is connected with the variable gain amplifier through the multiplexer; the output of the variable gain amplifier is connected with the analog-to-digital converter, the output of the analog-to-digital converter is connected with the FPGA, and the address gating output end and the gain control end of the FPGA are respectively connected with the multiplexer and the variable gain amplifier. The invention increases the dynamic range of the system by eliminating the direct current component, namely reflecting the detection distance of the system.

Description

FMCW laser radar system for eliminating direct current quantity and control method

Technical Field

The invention relates to the technical field of integrated circuits, in particular to an FMCW laser radar system for eliminating direct current and a control method thereof.

Background

The laser radar system is a system for detecting characteristic quantities such as a position and a speed of a target by emitting a laser signal, and is widely applied to the fields of unmanned driving, industrial measurement, robots, unmanned aerial vehicles, remote sensing and the like in recent years. Among them, frequency Modulated Continuous Wave (FMCW) laser radar has been a research hotspot due to its advantages of speed measurement, safety to human eyes, low laser power, and the like.

FMCW mainly sends and receives continuous laser beam, make echo light and local oscillator interfere, and utilize the frequency mixing detection technology to measure and send and frequency difference received, and then calculate the distance of the target object through frequency difference conversion. Specifically, the laser beam is reflected after hitting the target, and the reflection affects the frequency of the light — if the target moves toward the vehicle, the frequency increases; if the target object and the vehicle travel in the same direction, the frequency is reduced; when the reflected light returns to the detector, the difference between the two frequencies can be measured compared to the frequency at the time of transmission, and the distance information of the object can be calculated.

In the field of intelligent vehicle unmanned driving, laser radar has become a recognized indispensable technical means. Through on-vehicle laser detector, the intelligent vehicle can acquire the distance information of place ahead road and pedestrian, and the perception barrier realizes driver assistance and autopilot. In the laser ranging system, the longer the distance, the weaker the echo signal is; the closer the distance the stronger the echo signal. When the system is used for outdoor measurement, particularly under the conditions of severe weather such as rainy days, foggy days, snowy days and the like, the system is easily influenced by external environment background light or stray signal light, the signal-to-noise ratio is deteriorated, and the sensitivity is reduced, so that the farthest detection distance of the system is limited.

The detection distance of the laser radar system corresponds to the link input dynamic range, the wide input dynamic range can enable the detection range of the system to be wider, the detection distance to be farther, the detection precision to be higher, and meanwhile, the design difficulty is larger.

In practical application, the detector has direct current quantity and environmental light, etc., which can make the detector generate direct current quantity, especially, the photocurrent for processing in FMCW system is generated by the frequency mixing of local oscillator light and echo light and the response of the detector, the mixed light contains direct current quantity, the direct current quantity occupies partial dynamic range through the conversion and amplification of the receiving module, and further the detection distance and precision are reduced.

Therefore, how to eliminate the dc flow is an urgent problem to be solved, and the elimination of the dc flow in the system architecture mainly includes two ways: firstly, a plate level adopts an alternating current coupling mode, and a filter is formed by means of a capacitor resistor to filter out direct current quantity; and the second is to adopt a chip building system architecture with a direct current quantity elimination function. The first mode has large time constant corresponding to the resistance and the capacitance, delay and gain nonlinearity on signal transmission, and the existence of the capacitance limits the application in the development trend of line arrays and area arrays; the second way is to design the system architecture from a chip selection perspective, but currently only foreign model 2 chips (LTC 6563, LMH 32401) are available on the market and are difficult to procure for use due to contraband.

In order to eliminate the direct current quantity, increase the dynamic range, improve the detection distance of the system and provide convenience for the design of a subsequent detection processing circuit, an FMCW laser radar system architecture aiming at the direct current quantity elimination needs to be designed urgently, and echoes received by each element of a linear array or area array detector are processed, so that the FMCW laser radar system architecture is very valuable for the development of an array laser radar system.

In the related art, chinese patent publication No. CN106501789A describes a signal processing system architecture applied to an airborne laser radar, including an FPGA, a PMT detector, and a transimpedance amplifier, where the PMT detector converts a detected laser echo signal into a current signal; the method comprises the following steps that photocurrent is converted into an analog voltage signal through a transimpedance amplifier, the analog voltage signal output by the transimpedance amplifier is divided into three paths A, B and C, the three paths are respectively amplified by a high gain amplifier, a middle gain amplifier and a low gain amplifier, and then are respectively converted into digital signals through an ADC, namely, the digital signals are output signals of the submarine ADC; the FPGA receives output signals from the seabed ADC, sea surface data of a sea-land line scanning height measuring system and an electric local oscillation signal, so that control of a gate control circuit and measurement and calculation of seabed distance are achieved.

However, the application object of the scheme is TOF laser radar, the detector object is a PMT detector (photomultiplier tube), and the core function is that a trans-impedance amplifier realizes I-V conversion and A/B/C three-gear gain to respectively amplify output analog signals and respectively convert the analog signals into digital signals through an ADC.

Chinese patent publication No. CN112782670A describes a small-signal amplification circuit suitable for a laser radar analog front end, including: the self-triggering gain control circuit comprises an input circuit, a pre-amplifying circuit, a first-stage voltage amplifier, a second-stage voltage amplifier, a self-triggering enabling control circuit, a self-adaptive gain control circuit, a selector and an output circuit; the pre-amplifying circuit is connected with the input circuit; the first-stage voltage amplifier is connected with the pre-amplifying circuit; the second stage voltage amplifier is connected with the first stage voltage amplifier; the self-triggering enabling control circuit is connected with the second-stage voltage amplifier; the self-adaptive gain control circuit is connected with the pre-amplification circuit and the first-stage voltage amplifier; the self-adaptive gain control circuit is connected with the self-triggering enabling control circuit; the selector is connected with the pre-amplifying circuit, the first-stage voltage amplifier and the second-stage voltage amplifier; the selector is also connected with the self-adaptive gain control circuit; the output circuit is connected with the selector.

The application object of the scheme is TOF laser radar, the circuit module architecture is emphasized, the core comprises an input circuit, a pre-amplification circuit, a first-stage voltage amplifier, a second-stage voltage amplifier, a self-triggering enabling control circuit, a self-adaptive gain control circuit, a selector and an output circuit, and the core mainly realizes signal amplification; the dynamic range is related to a self-triggering enabling control circuit, a self-adaptive gain control circuit and a selector, wherein the self-adaptive gain control circuit consists of 2 comparators (respectively corresponding to two amplification modules at the front end) and a logic circuit, and the high and low levels of the output (S1, S2 and S3) of the self-adaptive gain control circuit respectively feed back and control the gain of the front end to prepare for the next detection, so that the dynamic range is enlarged.

Disclosure of Invention

The technical problem to be solved by the invention is how to provide an FMCW lidar system architecture aiming at direct current quantity elimination, and the dynamic range of the system is increased by eliminating the direct current quantity.

The invention solves the technical problems through the following technical means:

the invention provides an FMCW laser radar system aiming at direct current quantity elimination, which comprises the following components: the optical and detector module comprises a detector array, the signal amplification and conversion module comprises an analog amplification array, a differential-to-single-ended array, a multiplexer and a variable gain amplifier, the data processing module comprises an analog-to-digital converter and an FPGA chip, and the analog amplification array adopts a differential structure;

the output of the detector array is connected with the differential-to-single-ended array through the analog amplification array, and the output of the differential-to-single-ended array is connected with the variable gain amplifier through the multiplexer;

the output of the variable gain amplifier is connected with the analog-to-digital converter, the output of the analog-to-digital converter is connected with the FPGA chip, and the address gating output end and the gain control end of the FPGA chip are respectively connected with the multiplexer and the variable gain amplifier.

The echo photocurrent signal output by the detector is weak and is not easy to be processed in the later stage, and the echo photocurrent signal is converted and amplified by arranging the analog amplification array, so that the later stage processing is facilitated; the analog amplification array is of a differential structure to improve the noise suppression capability, the output of a channel of a multi-path selector for synchronously controlling a corresponding detector element is realized by adding a differential-to-single-ended array, the current signal strength difference when a target is close to or far away from the target and the influence of direct current quantity are considered, the gain of a receiving link is compensated by a variable gain amplifier, the amplitude of an output signal is controlled by changing a gain gear, and the elimination of the direct current quantity of a pixel corresponding to the detector is realized by the suppression of the differential structure to a common mode. The FMCW laser radar system for eliminating the direct current quantity provided by the invention replaces the traditional capacitance blocking scheme, can avoid large signal transmission delay and signal frequency component distortion, increases the dynamic range of the system by eliminating the direct current component, namely reflects the detection distance of the system, simultaneously increases the available space of useful signals by eliminating the direct current quantity, indirectly improves the signal-to-noise ratio, reduces the requirement on the signal-to-noise ratio of the rear end, and conforms to the development trend of laser radar lineup.

Further, the analog amplification array comprises a transimpedance amplifier array and a voltage amplifier array, the output of the detector array is connected with the transimpedance amplifier array, and the output of the transimpedance amplifier array is connected with the voltage amplifier array.

Further, the optical and detector module comprises an optical component and a detector array, wherein the optical component comprises a laser, a fiber coupler, a fiber circulator and a power spectroscope;

the optical fiber coupler is arranged on a continuous frequency sweeping laser path emitted by the laser, continuous frequency sweeping laser emitted by the laser is separated into two paths of optical components through the optical fiber coupler, the optical fiber circulator is arranged on the transmission path of one path of the optical components, and the power spectroscope is arranged at the intersection point of the transmission path of the other path of the optical components and the output optical path of the optical fiber circulator;

the output light path of the optical fiber circulator is provided with a target to be detected, and the output light path of the power spectroscope is provided with the detector array.

Further, the number of transimpedance amplifiers in the transimpedance amplifier array and the number of voltage amplifiers in the voltage amplifier array are the same as the number of detectors in the detector array; the total number of channels of the multiplexer is the same as the number of detectors in the detector array.

Further, the analog-to-digital converter adopts a time division multiplexing structure.

Furthermore, the present invention also provides a control method of the FMCW lidar system for dc cancellation as described above, the method comprising:

converting the echo photocurrent signal output by the optical and detector module into a voltage signal by using the signal amplification conversion module and amplifying the voltage signal to obtain a voltage amplification signal;

and the differential-to-single-ended array is utilized to realize the output synchronous control of the multiplexer on the detector channel in the optical and detector module, and output a voltage amplification signal to a variable gain amplifier, wherein the signal actually processed by the variable gain amplifier is delta V _in ：

ΔV _in ＝VIP-VIN＝2V _ac

VIP＝(V+V _dc )+V _ac

VIN＝(V+V _dc )-V _ac

In the formula: VIP, VIN are two input ends of the variable gain amplifier respectively; v is the bias voltage of the input terminal; v _dc Is the input terminal bias offset caused by the dc amount; v _ac Is the corresponding signal voltage after the AC quantity is amplified;

resolving the photoelectric signal output by the variable gain amplifier by using the data processing module, and calculating a target distance;

and controlling gating of the multiplexer and gain steps of the variable gain amplifier by using the data processing module.

Further, the converting module for converting the echo photocurrent signal output by the optical and detector module into a voltage signal and amplifying the voltage signal to obtain a voltage amplified signal includes:

converting the echo photocurrent signal into a voltage signal by using the transimpedance amplifier array;

and amplifying the voltage signal by using the voltage amplifier array to obtain the voltage amplified signal.

Further, the method further comprises:

separating the continuous sweep frequency laser emitted by the laser into two paths of first light components by using the optical fiber coupler;

one path of the light component is emitted by the optical fiber circulator and then irradiates a target, and echo light is generated;

the other path of the first light component is used as local oscillation light and echo light, and the local oscillation light and the echo light respectively generate two parts of second light components through the power spectroscope and output to the detector array in a frequency mixing manner;

generating two sets of photocurrents I using the detector array response _n1 And I _n2 The direct current flow of the two groups of photocurrents are equal in magnitude, the phase difference of the alternating current flow is 180 degrees, N =1,2 \8230, and N-1, N is the total number of the detectors in the detector array.

Further, the calculating, by the data processing module, the photoelectric signal output by the variable gain amplifier, and calculating the target distance includes:

converting the photoelectric signal output by the variable gain amplifier into a digital signal by using the digital-to-analog converter;

and resolving the digital signal by using the FPGA chip, and calculating a target distance.

Further, the controlling the gating of the multiplexer and the gain step of the variable gain amplifier by the data processing module includes:

receiving a laser emission synchronizing signal generated by the laser by using the FPGA chip, and controlling the multiplexer to perform detector address gating once when receiving the synchronizing signal once;

and adjusting the gain gear of the variable gain amplifier by utilizing the FPGA chip aiming at different output signal amplitudes of the variable gain amplifier.

The invention has the advantages that:

(1) The echo photocurrent signal output by the detector is weak and is not easy to be processed in the later stage, and the echo photocurrent signal is converted and amplified by arranging the analog amplification array, so that the later stage processing is facilitated; the analog amplification array is of a differential structure to improve the noise suppression capability, the output of a channel of a multi-channel selector for synchronously controlling a corresponding detector element is realized by adding a differential-to-single-ended array, the current signal strength difference when a target is close to or far away from the target and the influence of direct current quantity are considered, the gain of a receiving link is compensated by a variable gain amplifier, the amplitude of an output signal is controlled by changing a gain gear, and meanwhile, the elimination of the direct current quantity of a pixel element corresponding to the detector is realized by the suppression of the differential structure to a common mode. The FMCW laser radar system for eliminating the direct current quantity provided by the invention replaces the traditional capacitance blocking scheme, can avoid large signal transmission delay and signal frequency component distortion, increases the dynamic range of the system by eliminating the direct current component, namely reflects the detection distance of the system, simultaneously increases the available space of useful signals by eliminating the direct current quantity, indirectly improves the signal-to-noise ratio, reduces the requirement on the signal-to-noise ratio of the rear end, and conforms to the development trend of laser radar lineup.

(2) Photocurrent is converted into a voltage signal through a Transimpedance amplifier (TIA), each unit of a linear array or area array detector needs an independent Transimpedance amplifier, and in order to ensure excellent performance of a receiving link, gain of the TIA is not large generally, so that a post-stage voltage amplifier array compensation gain is needed to further amplify the signal.

(3) The analog-to-digital converter adopts a time-sharing multiplexing structure, so that the analog-to-digital converter is always in a working state, and data processing is sequentially read from corresponding elements of the array, thereby reducing the hardware cost.

(4) The FPGA chip performs hardware analysis and calculation on the acquired digital quantity signal, realizes laser ranging, and can improve indexes such as a system signal-to-noise ratio through an algorithm angle.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

Fig. 1 is a schematic structural diagram of an FMCW lidar system for dc cancellation according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of an optical and detector module according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of a signal amplifying and converting module according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a waveform for eliminating DC function according to an embodiment of the present invention;

FIG. 5 is a block diagram of a data processing module according to an embodiment of the present invention;

FIG. 6 is a timing diagram illustrating the gating of the FPGA chip control multiplexer according to an embodiment of the present invention;

fig. 7 is a flow chart illustrating a control method of the FMCW lidar system for dc cancellation according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, a first embodiment of the present invention proposes an FMCW lidar system for dc cancellation, the system including: the optical and detector module 10 comprises a detector array 11, the signal amplification and conversion module 20 comprises an analog amplification array 21, a differential-to-single-ended array 22, a multiplexer 23 and a variable gain amplifier 24, the data processing module 30 comprises an analog-to-digital converter 31 and an FPGA chip 32, and the analog amplification array 21 adopts a differential structure;

the output of the detector array 11 is connected to the differential-to-single-ended array 22 through the analog amplification array 21, and the output of the differential-to-single-ended array 22 is connected to the variable gain amplifier 24 through the multiplexer 23;

the output of the variable gain amplifier 24 is connected to the analog-to-digital converter 31, the output of the analog-to-digital converter 31 is connected to the FPGA chip 32, and the address gating output end and the gain control end of the FPGA chip 32 are connected to the multiplexer 23 and the variable gain amplifier 24, respectively.

In this embodiment, the echo photocurrent signal output by the detector array 11 in the optical and detector module 10 is weak and not easy to be processed in the subsequent stage, and the echo photocurrent signal is converted and amplified by the analog amplification array 21, so that the subsequent processing is facilitated; the analog amplification array 21 is a differential structure to improve the suppression capability of noise, the differential-to-single-ended array 22 is added to realize that the multiplexer 23 synchronously controls the output of the channel of the corresponding detector element, the gain of the receiving link is compensated by the variable gain amplifier 24 in consideration of the current signal intensity difference when the target is close to or far away from the target and the influence of direct current quantity, the amplitude of the output signal is controlled by changing the gain gear, and the suppression of the differential structure on the common mode realizes the elimination of the direct current quantity of the corresponding pixel of the detector.

The FMCW laser radar system for eliminating the direct current quantity provided by the embodiment of the invention replaces the traditional capacitance blocking scheme, can avoid large signal transmission delay and signal frequency component distortion, increases the dynamic range of the system by eliminating the direct current component, namely reflects the detection distance of the system, simultaneously increases the available space of useful signals by eliminating the direct current quantity, indirectly improves the signal-to-noise ratio, reduces the requirement on the signal-to-noise ratio of the rear end, and conforms to the development trend of laser radar lineup.

In one embodiment, as shown in fig. 2, the optical and detector module 10 includes an optical component and a detector array 11, the optical component includes a laser 12, a fiber coupler 13, a fiber circulator 14 and a power beam splitter 15, the detector array 11 is a unit, line or area array balanced detector;

the optical fiber coupler 13 is arranged on a continuous frequency sweeping laser path emitted by the laser 12, the continuous frequency sweeping laser emitted by the laser 12 is separated into two optical components through the optical fiber coupler 13, the optical fiber circulator 14 is arranged on a transmission path of one optical component, and the power beam splitter 15 is arranged at an intersection point of the transmission path of the other optical component and an output optical path of the optical fiber circulator 14;

the output light path of the fiber optic circulator 14 is arranged with a target to be measured, and the output light path of the power beam splitter 15 is arranged with the detector array 11.

It should be noted that in the FMCW lidar system, the detector module includes two identical detector arrays 11 to form a balanced detector pair, and generally a total of N or P electrodes PIN is selected.

Specifically, the laser 12 emits continuous sweep laser, power separation is achieved through the optical fiber coupler 13, one part of the optical component L1 is used for irradiating a target, and the other part of the optical component is used as local oscillation light L0 and echo light (reflected by the irradiated target) to perform frequency mixing so as to enhance the intensity of an echo light signal. Usually, the local oscillator light L0 occupies a smaller component of the total laser power, and most of the laser power is used as an irradiation target to collect the echo L _1r This is also related to the fact that the transmission attenuation of laser light in the atmosphere is large, and the influence factor is large.

Specifically, the optical and detector module 10 performs laser emission, echo (L1) and local oscillator light (L0) mixing, and a pair of balanced detectors composed of detector arrays N1 and N2 generates a photocurrent (I) in response to the generated photocurrent (I) _n1 And I _n2 ) In which I _n1 And I _n2 The DC component and the AC component are included, the DC component is equal, and the AC component is equal and opposite.

In one embodiment, as shown in fig. 3, the analog amplification array 21 includes a transimpedance amplifier array to which the output of the detector array 11 is connected and a voltage amplifier array to which the output of the transimpedance amplifier array is connected.

In one embodiment, the number of transimpedance amplifiers in the transimpedance amplifier array and the number of voltage amplifiers in the voltage amplifier array are the same as the number of detectors in the detector array 11; the total number of channels of the multiplexer 23 is the same as the number of detectors in the detector array 11.

It should be noted that, the echo photocurrent signal output by the detector is weak and not easy to be processed in the subsequent stage, the photocurrent is converted into a voltage signal by the transimpedance amplifier TIA, and each unit of the line array or area array detector needs an independent transimpedance amplifier, so that an equal amount of transimpedance amplifier arrays need to be arranged according to the number of detector units of the array detector. In order to ensure the excellent performance of a receiving link, the gain of the TIA is generally not too large, and a post-stage voltage amplifier array is required to compensate the gain and further amplify the signal.

Specifically, since the transimpedance amplifier and the voltage amplifier are differential structures to improve the noise suppression capability, in order to match the multiplexer 23 in the system, the differential-to-single-ended array 22 is added to realize the output synchronous control of the paths of the corresponding detector elements by the multiplexer 23, that is, the switch S1 (S2 \8230; SN) corresponding to the detector array 11N1 and the switch S1 (S2 \8230; SN) corresponding to the detector array 11N2 are synchronously controlled to be simultaneously closed or opened.

It should be noted that the multiplexer 23 may be single or plural, but the total number of channels N controlled by the multiplexer is equal to the number of elements of the detector array 11.

Specifically, the working principle of the signal conversion and amplification module is as follows: the transimpedance amplifier N1 and N2 are respectively connected with the detector N1 and N2 to complete the photocurrent I _n1 And I _n2 The voltage amplifiers N1 and N2 further amplify the signals, and the differential-to-single-ended N1 and N2 perform single-ended output processing on the differential signals of the front stage to obtain (V + V) _dc )+V _ac And (V + V) _dc )-V _ac Where V is the output common mode voltage, V _dc Is I _dc (DC photocurrent) is amplified to obtain V _ac Is a 1 _ac (AC photocurrent) was amplified. For a balanced detector, the outputs of the differential-to-single-ended N1 and the differential-to-single-ended N2 are directly connected to the input of the variable gain amplifier 24, so as to eliminate the dc component and further amplify the signal by means of the amplifier characteristics, and the gain of the balanced detector is controlled by the FPGA chip 32.

When the balanced detector is composed of N pairs of arrays, since the number of the variable gain amplifiers 24 (VGA) is 1, a multiplexer 23n is added between the differential-to-single-ended and the variable gain amplifiers 24 for implementing sequential gating. Assuming 4 pairs of balanced detectors, the multiplexer 23 is 4: the 1-to-4-to-1 switching function is adopted, S1, S2, S3 and S4 are respectively connected with the differential-to-single ends 11 and 12, the differential-to-single ends 21 and 22, the differential-to-single ends 31 and 32 and the differential-to-single ends 41 and 42, and only one switch is closed to pass gating at the same time. Among them, 11, 21, 31, 41 correspond to the differential-to-single-ended array 22N1, 12, 22, 32, 42 correspond to the differential-to-single-ended array 22N2.

In one embodiment, two input terminals VIP and VIN of the variable gain amplifier 24 correspond to the output terminals of the differential-to-single-ended N1 and N2, respectively:

VIP＝(V+V _dc )+V _ac

VIN＝(V+V _dc )-V _ac

where V is the bias voltage of the input terminal, V _dc Is the offset of the input bias voltage, V, caused by the DC component _ac Is the corresponding signal voltage after the amplification of the alternating current quantity.

Therefore, the signal actually processed by the variable gain amplifier 24 is Δ V _in And the DC quantity eliminating function is realized:

ΔV _in ＝VIP-VIN＝2V _ac 。

the system aims at reading, collecting and analyzing continuous optical signals after frequency mixing and eliminating direct current quantity in photocurrent, as shown in fig. 4, the optical signals after frequency mixing are converted into photocurrent through a detector, the photocurrent is converted into voltage signals with proper amplitude through signal amplification and conversion, and the voltage signals are collected through an analog-to-digital converter 31ADC and sent to an FPGA chip 32 for signal processing.

In an embodiment, as shown in fig. 5, the data processing module 30 includes an analog-to-digital converter 31ADC and a Field-Programmable Gate Array (FPGA), and mainly implements quantization of echo signals, gating control of the multiplexer 23, gain step selection of the variable gain amplifier 24, acquisition of echo data, analysis, calculation, and the like.

The photoelectric signal output by the variable gain amplifier 24 is converted into a digital signal after being quantized by the ADC, and the digital signal is received by the FPGA chip 32, and the FPGA chip 32 performs hardware analysis and calculation on the acquired data, so as to achieve laser ranging, and meanwhile, the indexes such as the signal-to-noise ratio of the system can be improved by an algorithm angle.

Further, the FPGA chip 32 is also configured to receive a laser emission synchronization signal generated by the laser 12, and each time the synchronization signal is received, it indicates that one cycle of the detection signal is completed. The FPGA controls one-time gating of the multiplexer 23, and each time a synchronization signal is received, it indicates that the gated address completes one-time detection of all elements of the array detector, and the sequential gating configuration of the multiplexer 23 is realized through the FPGA, as shown in fig. 6.

In one embodiment, the analog-to-digital converter 31 adopts a time-division multiplexing structure.

It should be noted that if all data are uploaded and analyzed, the requirement on the ADC is high, and a large amount of back-end resources are consumed by a large amount of data, and the data cannot be processed finally. Therefore, the time-sharing multiplexing structure is adopted, the ADC is always in a working state, and the data are sequentially read from the corresponding elements of the array for processing, so that the hardware cost is reduced.

In this embodiment, the optical and detector module 10 generates currents with the same dc amount and the same ac amount, the currents are converted and amplified by the transimpedance amplifier and the voltage amplifier, and finally the differential-to-single-ended and variable gain amplifier 24 eliminates the dc amount in the signal by the characteristics of the amplifier itself, so as to ensure that the final output is an effective signal component, thereby improving the dynamic range and the signal-to-noise ratio. The system architecture provides a solution for eliminating direct current of the FMCW laser radar, can realize direct current elimination, conversion amplification, collection, storage and analysis of each laser echo signal of a unit, a line array or an area array balanced detector, improves the signal-to-noise ratio, the dynamic range and the detection distance range of the system, conforms to the development trend of laser radar line array, and provides reference for the design of a subsequent laser radar system processing architecture.

Further, as shown in fig. 7, a second embodiment of the present invention proposes a control method of an FMCW lidar system for dc cancellation, the method including the steps of:

s10, converting the echo photocurrent signal output by the optical and detector module into a voltage signal by using the signal amplification and conversion module, and amplifying to obtain a voltage amplification signal;

s20, the multiplexer is used for realizing output synchronous control of the optical and detector module and the detector channel in the optical and detector module, and outputting a voltage amplification signal to a variable gain amplifier, wherein the signal actually processed by the variable gain amplifier is delta V _in ：

ΔV _in ＝VIP-VIN＝2V _ac

VIP＝(V+V _dc )+V _ac

VIN＝(V+V _dc )-V _ac

In the formula: VIP, VIN are the two inputs of the variable gain amplifier, respectively; v is the bias voltage of the input terminal; v _dc Is the input terminal bias offset caused by the dc amount; v _ac Is the corresponding signal voltage after the AC quantity is amplified;

s30, resolving the photoelectric signal output by the variable gain amplifier by using the data processing module, and calculating a target distance;

and S40, controlling gating of the multiplexer and gain gear of the variable gain amplifier by using the data processing module.

In the embodiment, the analog amplification array is used for converting and amplifying the echo photoelectric signals output by the optical and detector module, and finally, the difference is converted into the direct current quantity in the signals by the single end and the variable gain amplifier by virtue of the characteristics of the amplifier, so that the final output is the effective signal component, and the dynamic range and the signal-to-noise ratio are improved. Meanwhile, considering the current signal strength difference of the target when the distance is close and far and the influence of direct current quantity, the gain of the receiving link is compensated by the variable gain amplifier, and the amplitude of the output signal is controlled by changing the gain gear, namely, the high gear gain is configured in a long distance mode and the low gear gain is configured in a short distance mode.

In one embodiment, the step S10: the signal amplification conversion module is used for converting the echo photocurrent signal output by the optical and detector module into a voltage signal and amplifying the voltage signal to obtain a voltage amplification signal, and the method comprises the following steps:

In an embodiment, the method further comprises the steps of:

one path of the light component is emitted by the optical fiber circulator and then irradiates a target and generates echo light;

generating two sets of photocurrents I using the detector array response _n1 And I _n2 The direct current flow of the two groups of photocurrents is equal in magnitude, the phase difference of the alternating current flow is 180 degrees, N =1,2 \8230, and N-1, N is the total number of the detectors in the detector array.

Further, the laser emits continuous sweep frequency laser, power separation is achieved through the optical fiber coupler, one part of the optical component L1 is used for irradiating a target, and the other part of the optical component is used as local oscillation light L0 and echo light (obtained by reflecting the irradiated target) to be subjected to frequency mixing, so that the intensity of echo light signals is enhanced. Usually, the local oscillator light L0 occupies a small component of the total laser power, and most of the laser power is used as an irradiation target to collect the echo L1r, which is also related to that the transmission attenuation of the laser in the atmosphere is very large, and the influence factors are more, and the formula is as follows:

in the formula: p is _L1 Is the optical power of the light component L1, and a is the transmission efficiency of the laser light in the atmosphereρ is the target reflectance, A _r Is the area of the target and R is the target distance.

Furthermore, the local oscillation light and the echo light respectively generate 2 parts of light components through the power spectroscope and mix the light components, and the N pairs of balanced detectors formed by the detector arrays N1 and N2 respond to generate 2 corresponding groups of optical currents In1 and In2 (N =1,2 \8230; N-1, N), wherein the optical currents are characterized In that the direct current flows are equal In magnitude, the phase difference of the alternating current flows is 180 degrees, and the formula is as follows:

I _n1 ＝I _dc +I _ac

I _n2 ＝I _dc -I _ac

wherein, I _dc Is the direct current of the current, I _ac Is the alternating flow of current.

In one embodiment, the step S30: the data processing module is used for resolving the photoelectric signal output by the variable gain amplifier and calculating the target distance, and the method comprises the following steps:

and resolving the digital signal by using the FPGA chip to calculate the target distance.

In one embodiment, the step S40: the data processing module is used for controlling gating of the multiplexer and gain gears of the variable gain amplifier, and the method comprises the following steps:

the FPGA chip is used for receiving laser emission synchronizing signals generated by the laser, and the multi-path selector is controlled to carry out detector address gating once when the synchronizing signals are received once;

In the embodiment of the present invention, assuming that the line balance detector is 4 lines (2 identical 4 lines PIN), through the above analysis, the photocurrent generated by the detector arrays N1 and N2 is I _n1 And I _n2 (n =1,2,3,4), photoelectricThe currents are respectively subjected to I-V conversion through trans-impedance amplifiers in corresponding arrays, the voltage amplifiers further amplify signals, and the single-ended output of the signals is realized through differential conversion to single-ended output. The multiplexer is that 1,2 identical multiplexers from 4 are respectively connected with the differential-to-single-ended array, switches S1, S2, S3 and S4 in the multiplexer are respectively connected with 4 single-ended outputs in the differential-to-single-ended array, the sequential closing of S1, S2, S3 and S4 represents the gating of the signal output to the variable gain amplifier, the gating time sequence can be controlled by an FPGA chip as shown in figure 6, the high level represents the closing of the switch, and the T represents a set gating period which is generally consistent with the laser repetition frequency.

The 2 multiplexers respectively output a signal as an input signal of the variable gain amplifier, namely VIP and VIN, and the direct current voltage offset from the difference to the single end caused by the direct current is suppressed as a common mode through the variable gain amplifier, so that the direct current elimination function is realized, and a useful signal is further amplified and transmitted to the analog-to-digital converter. The gain of the variable gain amplifier is regulated and controlled through the FPGA chip, the output of the variable gain amplifier is sampled, quantized and read by the analog-to-digital converter and then analyzed by the FPGA, and the output value of the analog-to-digital converter is fed back to the variable gain amplifier by the FPGA to judge whether the gain needs to be changed or not.

Specifically, when the gain of the variable gain amplifier is in a 3-level gear (high, medium and low) and is discontinuously adjustable, the full scale range of the analog-to-digital converter is 1V, the variable gain amplifier is initially in a low-gain gear, and the output peak value of the variable gain amplifier is smaller than 500mV, the FPGA sends a command to configure the gain of the variable gain amplifier to be adjusted to a medium-gain gear, and if the output peak value of the variable gain amplifier is still smaller than 500mV, the FPGA sends a command to configure the gain of the variable gain amplifier to be adjusted to a high-gain gear; when the high gain gear is initially positioned and the output peak value is larger than 1V, the FPGA sends an instruction to configure the gain of the variable gain amplifier to be adjusted to the middle gain gear, and if the output peak value is still smaller than 1V, the FPGA sends an instruction to configure the gain of the variable gain amplifier to be adjusted to the high gain gear.

It should be noted that, the input dynamic range of the front-end processing circuit is an important performance index, and particularly for the FMCW laser radar system, a large amount of direct current is introduced by the presence of local oscillator light, and a large amount of direct current is introduced by ambient light such as sunlight, and the presence of the amount of direct current occupies a swing space of a useful signal, so that the dynamic range is reduced. The embodiment of the invention provides a system architecture for eliminating direct current quantity based on FMCW laser radar, which replaces the traditional capacitance blocking scheme to avoid large signal transmission delay and distortion of signal frequency components, increases the dynamic range of the system by eliminating the direct current components, namely reflects the detection distance of the system, simultaneously increases the available space of useful signals by removing the direct current quantity, indirectly improves the signal-to-noise ratio, reduces the requirement on the signal-to-noise ratio of a rear end, and conforms to the development trend of laser radar serialization.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. An FMCW lidar system for dc cancellation, the system comprising: the optical and detector module comprises a detector array, the signal amplification and conversion module comprises an analog amplification array, a differential-to-single-ended array, a multiplexer and a variable gain amplifier, the data processing module comprises an analog-to-digital converter and an FPGA chip, and the analog amplification array adopts a differential structure;

2. The FMCW lidar system for DC cancellation of claim 1, wherein the analog amplification array includes a transimpedance amplifier array and a voltage amplifier array, an output of the detector array being connected to the transimpedance amplifier array, an output of the transimpedance amplifier array being connected to the voltage amplifier array.

3. The FMCW lidar system for dc cancellation of claim 1, wherein the optics and detector module comprises an optics assembly and a detector array, the optics assembly comprising a laser, a fiber coupler, a fiber circulator, and a power splitter, the detector array being a cell, line, or area array balanced detector;

4. The FMCW lidar system for dc cancellation of claim 2, wherein the number of transimpedance amplifiers in the transimpedance amplifier array, the number of voltage amplifiers in the voltage amplifier array, and the number of detectors in the detector array are the same; the total number of channels of the multiplexer is the same as the number of detectors in the detector array.

5. The FMCW lidar system for dc cancellation of claim 1, wherein the analog-to-digital converter employs a time division multiplexing architecture.

6. A control method of an FMCW lidar system for DC cancellation according to any of claims 1-5, wherein said method comprises:

ΔV _in ＝VIP-VIN＝2V _ac

VIP＝(V+V _dc )+V _ac

VIN＝(V+V _dc )-V _ac

7. The method as claimed in claim 6, wherein the step of converting the echo photocurrent signal outputted from the optical and detector module into a voltage signal and amplifying the voltage signal by the signal amplification and conversion module to obtain a voltage amplified signal comprises:

8. The method for controlling an FMCW lidar system for dc cancellation according to claim 6, wherein said method further comprises:

9. The method for controlling an FMCW lidar system for dc cancellation according to claim 6, wherein the calculating the target distance using the data processing module to calculate the photoelectric signal output from the variable gain amplifier comprises:

10. The method for controlling an FMCW lidar system for dc cancellation according to claim 6, wherein the controlling the gating of the multiplexer and the gain step of the variable gain amplifier using the data processing module includes: