Radar device

Abstract

To provide a radar device capable of reducing distance calculation errors.SOLUTION: A radar device includes: a light source 20 that outputs an optical signal including a chirp signal; a transmitting / receiving unit 30 that transmits an output signal of the light source 20 and receives the optical signal to generate a received signal; a beat frequency measurement unit 40 that generates a first beat signal by causing interference between the output signal and the received signal and measures a beat frequency of the first beat signal; a chirp rate measurement unit 50 that measures a chirp rate of the output signal; and a ranging calculation unit 60 that calculates a distance to a target by using the beat frequency measured by the beat frequency measurement unit 40 and the chirp rate measured by the chirp rate measurement unit 50.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a radar device. [Background technology]

[0002] FMCW radar devices, such as LiDAR, generate and transmit a frequency-swept chirp signal. The original chirp signal interferes with the light reflected from the target to generate a beat signal. The frequency difference between the transmitted signal and the received signal, which varies depending on the distance between the radar device and the target, is detected as a beat frequency. The distance between the radar device and the target is calculated based on the beat frequency and the chirp rate. To accurately calculate the distance in such radar devices, the chirp rate must be accurately determined. FMCW stands for Frequency Modulated Continuous Wave. LiDAR stands for Light Detection and Ranging.

[0003] For example, Non-Patent Document 1 proposes a technique for linearizing the output signal of a light source by a predistortion method, thereby enabling the chirp rate to be determined accurately. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Peng Li, Yating Zhang, Jianquan Yao, "Rapid Linear Frequency Swept Frequency-Modulated Continuous Wave Laser Source Using Iterative Pre-Distortion Algorithm", Remote Sens. 2022, 14, 3455 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the predistortion method has low robustness against environmental changes such as temperature changes, and in applications such as in-vehicle applications, the actual chirp rate deviates from the set value, resulting in large errors in distance calculations.

[0006] In view of the above, an object of the present disclosure is to provide a radar device that can reduce distance calculation errors. [Means for solving the problem]

[0007] In order to achieve the above object, according to one aspect of the present disclosure, a radar device includes a light source (20) that outputs an optical signal including a chirp signal, a transceiver unit (30) that transmits the output signal of the light source and receives the optical signal to generate a received signal, a beat frequency measurement unit (40) that generates a first beat signal by causing interference between the output signal and the received signal and measures the beat frequency of the first beat signal, a chirp rate measurement unit (50) that measures the chirp rate of the output signal, and a ranging calculation unit (60) that calculates the distance to a target using the beat frequency measured by the beat frequency measurement unit and the chirp rate measured by the chirp rate measurement unit.

[0008] In this way, by measuring the chirp rate of the output signal of the light source and calculating the distance using the measured chirp rate, the robustness of the distance calculation accuracy can be improved and the distance calculation error can be reduced.

[0009] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a radar device according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating a configuration of a beat frequency measurement unit. [Figure 3]FIG. 2 is a diagram illustrating frequencies of transmitted and received signals. [Figure 4] FIG. 2 is a diagram showing the configuration of a chirp rate measurement unit. [Figure 5] FIG. 10 is a diagram showing a calculation error of the chirp rate. [Figure 6] FIG. 10 is a diagram illustrating a distance calculation error. [Figure 7] FIG. 10 is a diagram showing the configuration of a chirp rate measurement unit in the second embodiment. [Figure 8] FIG. 4 is a diagram illustrating the amplitude of a beat signal. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the following embodiments, identical or equivalent parts will be denoted by the same reference numerals.

[0012] (First embodiment) A first embodiment will be described below. A radar device 1 is an FMCW radar device, and is mounted on a vehicle, for example, and used as a target detection device that detects targets around the vehicle.

[0013] 1, the radar device 1 includes a driving unit 10, a light source 20, a transmitting / receiving unit 30, a beat frequency measuring unit 40, a chirp rate measuring unit 50, and a ranging calculation unit 60. The driving unit 10 to the ranging calculation unit 60 are configured, for example, as an integrated chip formed on an SOI (Silicon on Insulator) substrate using silicon photonics, but some of these may be configured separately from the other parts.

[0014] The driving unit 10 generates a driving signal for driving the light source 20. The driving unit 10 is electrically connected to the light source 20 by metal wiring such as aluminum (Al) formed on an SOI substrate, a through-silicon via (TSV), a ball grid array, wire bonding, or the like, and the driving signal generated by the driving unit 10 is input to the light source 20.

[0015] The light source 20 outputs an optical signal corresponding to the drive signal input from the driver 10. The light source 20 is configured, for example, by a laser diode, and generates light when supplied with current from the driver 10. The light source 20 is connected to the transmitter / receiver 30 by a waveguide consisting of a core layer made of Si (silicon) or the like and a clad layer made of SiO2 (silicon oxide) or the like. This waveguide also branches between the light source 20 and the transmitter / receiver 30 and is connected to the beat frequency measurement unit 40 and the chirp rate measurement unit 50. The output signal of the light source 20 is input to the transmitter / receiver 30, the beat frequency measurement unit 40, and the chirp rate measurement unit 50.

[0016] The frequency of the output signal from the light source 20 varies depending on the current value of the drive signal input from the drive unit 10. The drive unit 10 generates the drive signal so that the output signal from the light source 20 contains a chirp signal whose frequency varies in a triangular wave shape.

[0017] The driver 10 generates a drive signal by using a predistortion method to linearly correct the nonlinearity of the output signal from the light source 20. In other words, if distortion occurs in the output signal from the light source 20 relative to the drive signal from the driver 10, the current value of the drive signal from the driver 10 is adjusted in a direction that cancels out this distortion.

[0018] The transceiver 30 transmits the output signal of the light source 20 as a transmission signal to the outside of the radar device 1, and receives an optical signal arriving from the outside of the radar device 1 and generates a reception signal corresponding to the received optical signal. The transceiver 30 includes an optical amplifier 31 and a scanning unit 32, and the output signal of the light source 20 is input to the optical amplifier 31.

[0019] The optical amplifier 31 amplifies the output signal of the light source 20. The optical amplifier 31 is connected to the scanning unit 32 by a waveguide. The output signal of the light source 20 is amplified by the optical amplifier 31 and then input to the scanning unit 32.

[0020] The scanning unit 32 is configured with an OPA (Optical Phased Array) in which waveguides are branched and arranged in parallel, with optical signals emitting and receiving from the ends of each waveguide. A phase shifter is disposed in each waveguide, and by controlling the phase of the light propagating through each waveguide using the phase shifter, the emitting and receiving directions of light from the entire scanning unit 32 can be controlled. The scanning unit 32 periodically changes the phase of the light propagating through each waveguide, thereby changing the directivity of the light emitted from the entire scanning unit 32 and scanning the transmission signal in any direction. The scanning unit 32 also generates a receiving signal corresponding to the received optical signal.

[0021] The scanning unit 32 is connected to the beat frequency measuring unit 40 by a waveguide. The received signal generated by the scanning unit 32 is input to the beat frequency measuring unit 40.

[0022] The beat frequency measuring section 40 generates a first beat signal by causing interference between the output signal of the light source 20 and the received signal input from the transmitting / receiving section 30, and measures the beat frequency of the first beat signal.

[0023] 2, the beat frequency measurement unit 40 includes an IQ detector 41, an optical detection unit 42, an ADC (Analog to Digital Converter) 43, and an FFT (Fast Fourier Transform) processing unit 44. The light source 20 and the transceiver unit 30 are connected to the IQ detector 41 by waveguides, and the output signal of the light source 20 and the received signal of the transceiver unit 30 are input to the IQ detector 41.

[0024] The IQ detector 41 multiplexes the output signal from the light source 20 and the received signal from the transmitter / receiver 30, and performs IQ detection on the multiplexed signal thus generated to generate a complex signal. The IQ detector 41 is connected to the photodetector 42 by a waveguide, and the complex signal generated by the IQ detector 41 is input to the photodetector 42.

[0025] The photodetector 42 converts the complex signal input from the IQ detector 41 from an optical signal into a first beat signal, which is an electrical signal. The photodetector 42 is configured, for example, with a balanced photodetector. The photodetector 42 is connected to the ADC 43 by metal wiring or the like, and the electrical signal generated by the photodetector 42 is input to the ADC 43.

[0026] The ADC 43 performs AD conversion on the electrical signal input from the photodetector 42. The ADC 43 is connected to the FFT processor 44 by metal wiring or the like, and the digital signal generated by the ADC 43 is input to the FFT processor 44.

[0027] The FFT processor 44 performs FFT processing on the digital signal input from the ADC 43. A time difference and a frequency difference occur between the transmitted signal and the received signal depending on the distance between the radar device 1 and the target that reflected the transmitted signal, and the relative speed of the target with respect to the radar device 1. For example, when a target is approaching the radar device 1, the frequencies of the transmitted signal and the received signal change as shown in Fig. 3. In Fig. 3, the solid line indicates the transmitted signal, the dashed-dotted line indicates the received signal when the relative speed of the target is 0, and the dashed-two-dotted line indicates the received signal when the target is approaching the radar device 1.

[0028] The time difference between the transmitted signal and the received signal is Dis. The frequency difference between the up-chirp of the transmitted signal and the up-chirp of the received signal is f. up The frequency difference between the down-chirp of the transmitted signal and the down-chirp of the received signal is f down If the frequency sweep time of the chirp signal is T, the frequency sweep width is B, and the chirp rate is γ, then γ = B / T.

[0029] The first beat signal has a frequency difference f up , f down appears as the beat frequency. Then, by FFT processing of the first beat signal, this beat frequency f up , f downThe FFT processing unit 44 is connected to the distance measurement calculation unit 60 by metal wiring or the like, and the beat frequency extraction result by the FFT processing unit 44 is input to the distance measurement calculation unit 60.

[0030] The chirp rate measurement unit 50 measures the chirp rate of the output signal from the light source 20. As shown in Fig. 4, the chirp rate measurement unit 50 includes an internal interference system 51, a photodetector 52, an ADC 53, a beat frequency calculator 54, and a chirp rate calculator 55.

[0031] The internal interference system 51 generates an optical interference signal from the output signal of the light source 20. Specifically, the internal interference system 51 is configured as a delayed self-heterodyne interferometer that generates an optical interference signal by causing interference between the output signal of the light source 20 and a delayed signal obtained by delaying the output signal of the light source 20. The internal interference system 51 is connected to the optical detection unit 52 by a waveguide, and the optical interference signal generated by the internal interference system 51 is input to the optical detection unit 52.

[0032] The photodetector 52 converts the optical interference signal input from the internal interference system 51 from an optical signal into a second beat signal, which is an electrical signal. The photodetector 52 is configured, for example, by a balanced photodetector. The photodetector 52 is connected to the ADC 53 by metal wiring or the like, and the electrical signal generated by the photodetector 52 is input to the ADC 53.

[0033] The ADC 53 performs AD conversion on the electrical signal input from the photodetector 52. The ADC 53 is connected to the beat frequency calculator 54 by metal wiring or the like, and the digital signal generated by the ADC 53 is input to the beat frequency calculator 54.

[0034] The beat frequency calculation unit 54 converts the second beat signal into the frequency domain and calculates the beat frequency of the second beat signal. Specifically, the beat frequency calculation unit 54 performs FFT processing on the signal input from the ADC 53 and extracts the beat frequency of the second beat signal. This beat frequency is the frequency difference between the up-chirp and down-chirp of the output signal from the light source 20 and a delayed signal obtained by delaying the output signal from the light source 20. The beat frequency calculation unit 54 is connected to the chirp rate calculation unit 55 by metal wiring or the like, and the beat frequency extraction result by the beat frequency calculation unit 54 is input to the chirp rate calculation unit 55.

[0035] The chirp rate calculation unit 55 calculates the chirp rate of the output signal from the light source 20 based on the beat frequency calculated by the beat frequency calculation unit 54. Specifically, the chirp rate calculation unit 55 calculates the chirp rate using Equation 1.

[0036]

number

[0037] The chirp rate calculation unit 55 is connected to the distance measurement calculation unit 60 by metal wiring or the like, and the chirp rate calculation result by the chirp rate calculation unit 55 is input to the distance measurement calculation unit 60.

[0038] The chirp rate measurement unit 50 measures the chirp rate multiple times within the sweep time T, calculates the time average of the multiple measurement results, and inputs the calculated result to the ranging calculation unit 60. Specifically, the beat frequency calculation unit 54 and the chirp rate calculation unit 55 perform FFT processing and chirp rate calculation for each sampling by the ADC 53. However, when switching between up-chirp and down-chirp, the abrupt change in the frequency change rate increases the chirp rate calculation error. Therefore, the chirp rate measurement unit 50 selects an arbitrary time domain from the time domain included in the sweep time T, avoiding the time around the time when the chirp switches between up-chirp and down-chirp, and time-averages the measured chirp rate values ​​in the selected time domain and inputs the result to the ranging calculation unit 60.

[0039] 5, the plots of black circles represent the chirp rate calculated by the chirp rate calculation unit 55 for each sampling in the ADC 53. The area surrounded by the dashed line is the area where the chirp rate calculation error increases due to switching between up-chirp and down-chirp. The chirp rate measurement unit 55 selects times t1 to tn from a time domain a predetermined time after the switching time between up-chirp and down-chirp, where n is an integer of 2 or greater, and inputs the average of the n calculation results for times t1 to tn to the ranging calculation unit 60.

[0040] The distance measurement calculation unit 60 calculates the distance to the target using the beat frequency measured by the beat frequency measurement unit 40 and the chirp rate measured by the chirp rate measurement unit 50. Specifically, the distance measurement calculation unit 60 calculates the distance using Equation 1. Here, R is the distance between the radar device 1 and the target, and f down , f up is the beat frequency measured by the beat frequency measurement unit 40, and γ is the chirp rate measured by the chirp rate measurement unit 50.

[0041] The effects of this embodiment will now be described. The solid line in FIG. 6 shows the results of a simulation of the relationship between the chirp rate error used in the calculation by the distance measurement calculation unit 60 and the error in the calculated distance. Point P1 shows the theoretical value of the distance calculation error in this embodiment. Point P2 shows the measurement result of an actual device in a comparative example in which distance measurement calculation was performed using the chirp rate setting value in the distance measurement calculation unit 60. In this simulation and measurement, the sweep time T of the output signal from the light source 20 was set to 10 μs, and the frequency sweep width B was set to 0.5 GHz. As shown in FIG. 6, in this embodiment, the chirp rate error and distance calculation error are reduced compared to the comparative example.

[0042] As described above, in this embodiment, the chirp rate of the output signal from light source 20 is measured, and the measured chirp rate is used to calculate the distance. This improves the robustness of the distance calculation accuracy, and therefore reduces distance calculation errors when the chirp rate deviates from a set value due to temperature changes or the like.

[0043] Furthermore, according to the above embodiment, the following effects can be obtained.

[0044] (1) The chirp rate measurement unit 50 calculates the chirp rate from the result of FFT processing of the second beat signal. This makes it possible to measure the chirp rate with a simpler configuration than the second embodiment described later.

[0045] (2) The chirp rate measurement unit 50 measures the chirp rate multiple times within the sweep time T, calculates the time average of the multiple measurement results, and inputs the calculated result to the distance measurement calculation unit 60. This reduces the chirp rate measurement error.

[0046] (Second embodiment) The second embodiment will be described. This embodiment is different from the first embodiment in that the configuration of the chirp rate measurement unit 50 is changed, but other aspects are the same as those of the first embodiment, so only the differences from the first embodiment will be described.

[0047] 7, the chirp rate measuring section 50 of this embodiment includes an IQ detector 56 and an instantaneous frequency calculating section 57. The output signal of the internal interference system 51 is input to the IQ detector 56.

[0048] The IQ detector 56 performs IQ detection on the optical interference signal generated by the internal interference system 51 to generate a complex signal. The complex signal generated by the IQ detector 56 is input to the optical detection unit 52 and converted into a second beat signal, which is an electrical signal, and then converted into a digital signal by the ADC 53, and then input to the instantaneous frequency calculation unit 57.

[0049] The instantaneous frequency calculation unit 57 calculates the instantaneous frequency of the second beat signal based on the digital signal input from the ADC 53. Specifically, the instantaneous frequency calculation unit 57 calculates the phase from the input signal and calculates the instantaneous frequency using Equation 2.

[0050]

number

[0051] The chirp rate calculation unit 55 calculates the chirp rate by time differentiation of the instantaneous frequency calculated by the instantaneous frequency calculation unit 57. That is, the chirp rate calculation unit 55 calculates the chirp rate γ(t) using Equation 3.

[0052]

number

[0053] The calculation of the instantaneous frequency and the chirp rate by the instantaneous frequency calculation unit 57 and the chirp rate calculation unit 55 are performed for each sampling by the ADC 53. The chirp rate measurement unit 50 measures the chirp rate multiple times within the sweep time T, calculates the time average of the multiple measurement results, and inputs the calculated result to the distance measurement calculation unit 60.

[0054] This embodiment has the same configuration and operation as the first embodiment, and can therefore obtain the same effects as the first embodiment.

[0055] Furthermore, according to the above embodiment, the following effects can be obtained.

[0056] (1) The chirp rate measurement unit 50 converts the complex signal generated by IQ detecting the optical interference signal into a second beat signal, calculates the instantaneous frequency of the second beat signal, and calculates the chirp rate from this instantaneous frequency. This allows for more accurate measurement of the chirp rate than a method of calculating the beat frequency of the second beat signal using FFT, even if the chirp rate changes during the sweep due to temperature changes or the like and the output signal from the light source 20 becomes nonlinear.

[0057] (Third embodiment) The third embodiment will be described. This embodiment is different from the first embodiment in that the configuration of the chirp rate measurement unit 50 is changed, but other aspects are the same as the first embodiment, so only the differences from the first embodiment will be described.

[0058] The chirp rate measurement unit 50 of this embodiment calculates the chirp rate from the sampling results of the zero-crossing points of the second beat signal. Specifically, the beat frequency calculation unit 54 acquires the times at which the amplitude becomes 0 in the waveform of the second beat signal as shown in Fig. 8, and calculates the beat frequency from the interval between these times. Then, the chirp rate calculation unit 55 uses the beat frequency calculated in this manner to calculate the chirp rate in the same way as in the first embodiment.

[0059] This embodiment has the same configuration and operation as the first embodiment, and can therefore obtain the same effects as the first embodiment.

[0060] Furthermore, according to the above embodiment, the following effects can be obtained.

[0061] (1) The chirp rate measurement unit 50 calculates the chirp rate from the sampling results of the zero-crossing points of the second beat signal. This reduces the computational load compared to when FFT processing or calculation of the instantaneous frequency is performed.

[0062] (Other embodiments) The present disclosure is not limited to the above-described embodiments and can be modified as appropriate. It goes without saying that, in each of the above-described embodiments, the elements constituting the embodiments are not necessarily essential unless expressly stated as essential or clearly considered essential in principle. Furthermore, in each of the above-described embodiments, when numerical values ​​such as the number, numerical value, amount, and range of the components of the embodiments are mentioned, they are not limited to the specific number unless expressly stated as essential or clearly limited to a specific number in principle.

[0063] In each of the above embodiments, the chirp rate measurement unit 50 measures the chirp rate multiple times within the sweep time T and calculates the time average of the multiple measurement results, but this time average calculation may be performed multiple times and the average value of the multiple calculation results may be input to the distance measurement calculation unit 60. This improves the robustness of distance measurement against variations in chirp rate.

[0064] A complex signal may be generated from the combined signal using a Hilbert transform instead of IQ detection. Also, in the second embodiment, a complex signal may be generated from the optical interference signal using a Hilbert transform instead of IQ detection. The Hilbert transform processing may be performed, for example, in a calculation device that constitutes the FFT processing unit 44, the beat frequency calculation unit 54, the chirp rate calculation unit 55, the ranging calculation unit 60, etc. This eliminates the need for hardware for the IQ detectors 41 and 56, thereby enabling the radar device 1 to be made smaller. [Explanation of symbols]

[0065] 20 light source 30 Transmitter / Receiver 40 Beat frequency measurement section 50 Chirp rate measurement section 60 Distance calculation section

Claims

1. A radar device, a light source (20) that outputs an optical signal including a chirp signal; a transceiver (30) that transmits an output signal from the light source and receives an optical signal to generate a received signal; a beat frequency measurement unit (40) that generates a first beat signal by causing interference between the output signal and the received signal and measures the beat frequency of the first beat signal; a chirp rate measurement unit (50) for measuring the chirp rate of the output signal; a ranging calculation unit (60) that calculates the distance to the target using the beat frequency measured by the beat frequency measurement unit and the chirp rate measured by the chirp rate measurement unit.

2. 2. The radar device according to claim 1, further comprising a driver (10) for correcting nonlinearity of the output signal by a predistortion method.

3. The chirp rate measurement unit includes an internal interference system (51) that generates an optical interference signal from the output signal, converting the optical interference signal into a second beat signal; 2. The radar device according to claim 1, wherein the chirp rate is calculated by transforming the second beat signal into a frequency domain.

4. 4. The radar device according to claim 3, wherein the chirp rate measurement unit converts the second beat signal into a frequency domain to calculate a beat frequency, and calculates the chirp rate based on the beat frequency.

5. The radar device according to claim 3 , wherein the chirp rate measurement unit calculates the chirp rate from a result of FFT processing of the second beat signal.

6. The radar device according to claim 3 , wherein the chirp rate measurement unit calculates the chirp rate from a sampling result of a zero-cross point of the second beat signal.

7. 4. The radar device according to claim 3, wherein the chirp rate measurement unit converts a complex signal generated by IQ detection of the optical interference signal into the second beat signal, and calculates an instantaneous frequency of the second beat signal.

8. The radar device according to claim 7 , wherein the chirp rate measurement unit calculates the chirp rate from the instantaneous frequency.

9. 4. The radar device according to claim 3, wherein the internal interference system is configured as a self-delayed heterodyne interference system that generates the optical interference signal by causing interference between the output signal and a delayed signal obtained by delaying the output signal.

10. Let T be the sweep time of the frequency of the chirp signal, 2. The radar device according to claim 1, wherein the chirp rate measurement unit measures the chirp rate a plurality of times within the sweep time T, calculates a time average of the plurality of measurement results, and inputs the calculated result to the ranging calculation unit.

11. The radar device according to claim 10 , wherein the chirp rate measurement unit calculates the time average a plurality of times and inputs an average value of the plurality of calculation results to the distance measurement calculation unit.

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