The present disclosure relates to a radar device that performs detection of a target.
Patent Literature 1 listed below discloses a frequency modulation technique applicable to a fast chirp modulation (FCM) radar. The FCM radar has characteristics of facilitation of fabrication, a relatively low frequency band of a transmitted and received beat signals subject to baseband processing, and thus easy handling thereof. Due to such characteristics, the FCM radar has been widely used as an automobile anti-collision millimeter wave radar, and has been expected to be used as prospective one of sensors for automatic driving in the future.
However, the FCM radar described in Patent Literature 1 listed above has a configuration in which an analog to digital converter (ADC) is connected for each receiving channel. Therefore, as the number of receiving channels of the FCM radar increases, the number of ADCs also increases, and there is a problem that the size, manufacturing cost, and power consumption of the FCM radar increase.
The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a radar device capable of preventing an increase in size, manufacturing cost, and power consumption thereof even when the number of receiving channels increases.
In order to solve the above problem and achieve the object, the present disclosure provides a radar device comprising: an antenna unit to emit a radar wave into space; a high frequency circuit to receive a reflected wave of the radar wave from a target via the antenna unit; and a baseband circuit to convert a received signal outputted from the high frequency circuit into a baseband signal having a digital value, wherein the radar device has a first mode set to detect the target at a relatively long distance and a second mode set to detect the target at a relatively short distance, four or more receiving channels are configured in the antenna unit, the high frequency circuit, and the baseband circuit, a receiving channel number that is the number of the receiving channels on which conversion processing to the baseband signal is performed is smaller in the second mode than in the first mode, and a speed of the conversion processing is higher in the second mode than in the first mode.
The radar device according to the present disclosure has an advantageous effect that it can prevent an increase in size, manufacturing cost, and power consumption thereof even when the number of receiving channels increases.
Hereinafter, a radar device according to an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. Note that in the following embodiment, an FCM radar will be described as an example, the intent of which is not to exclude application to radar devices other than the FCM radar. Also, in the following description, electrical connection and physical connection are not particularly distinguished from each other and simply referred to as “connection”.
The antenna unit 16 includes a receiving array 16a and a transmitting array 16b. The receiving array 16a includes receiving antennas 11 to 18. The transmitting array 16b includes transmitting antennas 21 and 22. In a case where the radar device 100 is used as an automobile anti-collision millimeter wave radar, the receiving antennas 11 to 18 and the transmitting antennas 21 and 22 are arranged in a horizontal direction and in a direction orthogonal to a traveling direction of an automobile. Note that, hereinafter, the receiving antennas 11 to 18 may be referred to as “first receiving antenna” to “eighth receiving antenna”, respectively.
The subscript in the reference numeral of each of the receiving antennas 11 to 18 and the transmitting antennas 21 and 22 is attached for identification of a channel (ch). Note that, in the following description, the receiving antennas 11 to 18 will be denoted as a “receiving antenna 1” without the subscript when not individually distinguished from one another, and the transmitting antennas 21 and 22 will be denoted as a “transmitting antenna 2” without the subscript when not individually distinguished from each other. This notation is also applied to other components described below that are identified by attached subscripts.
Moreover, the channel is a collective processing unit involved in component elements of the transceiver unit and the signal processing unit, performed by one receiving antenna 1 or one transmitting antenna 2. Hereinafter, the channel of the receiving antenna 1 will be referred to as a “receiving channel”, and the channel of the transmitting antenna 2 will be referred to as a “transmitting channel”. In
The high frequency circuit 17 includes a voltage controlled oscillator (VCO) 7, a loop filter (LF) 8, a phase locked loop (PLL) 9, and a chirp signal generator 10 that is a device configured to generate a chirp signal. Hereinafter, the “voltage controlled oscillator” will be referred to as a “VCO”, the “loop filter” will be referred to as an “LF”, and the “phase locked loop” will be referred to as a “PLL”. The VCO 7, the LF 8, the PLL 9, and the chirp signal generator 10 constitute a local unit 17a.
The high frequency circuit 17 also includes power amplifiers (PAs) 61 and 62, low noise amplifiers (LNAs) 31 to 38, mixers (MIXs) 41 to 48, and intermediate frequency amplifiers (IFAs) 51 to 58. Hereinafter, the “power amplifier” will be referred to as a “PA”, the “low noise amplifier” will be referred to as an “LNA”, the “mixer” will be referred to as an “MIX”, and the “intermediate frequency amplifier” will be referred to as an “IFA”.
The baseband circuit 18 includes base band amplifiers (BBAs) 111 to 118, band pass filters (BPFs) 121 to 128, multiplexers (MUXs) 201 to 204, ADCs 131 to 134, and finite impluse response filters (FIRs) 141 to 148. The FIR filter is an example of a digital filter. Hereinafter, the “base band amplifier” will be referred to as a “BBA”, the “bandpass filter” will be referred to as a “BPF”, and the “multiplexer” will be referred to as an “MUX”. The “FIR filter” will be abbreviated as “FIR”. Also, hereinafter, the MUXs 201 to 204 may be referred to as “first multiplexer” to “fourth multiplexer”, respectively.
The MCU 19 includes fast Fourier transform (FFT) processing units 151 to 158 configured to perform fast Fourier transform as Fourier transform processing. Hereinafter, the “FFT processing unit” will be abbreviated as an “FFT”.
Next, a basic operation of the radar device 100 will be described.
The PLL 9 receives, as its inputs, the reference signal REF and the chirp signal generated by the chirp signal generator 10. The PLL 9 performs frequency modulation of the reference signal REF with a modulation pattern based on the chirp signal. The signal that has been frequency-modulated by the PLL 9 is band-limited by the LF 8 and inputted to the VCO 7. The VCO 7 cooperates with the PLL 9 to output a high frequency signal that has been frequency-modulated. The high frequency signal outputted from the VCO 7 includes a sawtooth wave up-chirp signal or a sawtooth wave down-chirp signal. The up-chirp signal is a signal whose frequency increases with a lapse of time. The down-chirp signal is a signal whose frequency decreases with a lapse of time.
The PA 6 amplifies the high frequency signal to have a desired electric power, and outputs the amplified high frequency signal to the transmitting antenna 2. The transmitting antenna 2 converts the high frequency signal into a radar wave that is a radio wave, and emits the radar wave obtained by the conversion into space.
The high frequency circuit 17 has a function of receiving a reflected wave of the transmitted radar wave from a target via the receiving array 16a of the antenna unit 16, and transmitting the received signal to the baseband circuit 18 situated in the subsequent stage.
In order to implement the above-mentioned function, the LNA 3 amplifies the received signal. The MIX 4 down-converts the signal outputted from the LNA 3 using a local signal outputted from the local unit 17a. The IFA 5 amplifies the down-converted signal to have a desired signal strength. Note that in the FCM radar, the local signal is linearly modulated. As a result, the signal outputted from the MIX 4 is generally a sine wave signal. Hereinafter, the signal outputted from the high frequency circuit 17 will be referred to as a “received signal”.
The baseband circuit 18 has a function of converting the received signal outputted from the high frequency circuit 17 into a baseband signal having a digital value.
In order to implement the above-mentioned function, the BBA 11 amplifies the received signal outputted from the high frequency circuit 17. The BPF 12 limits a band of the signal amplified by the BBA 11. The signal band-limited by the BPF 12 is transmitted to the ADC 13 via the MUX 20. Details of the configuration and operation of the MUX 20 will be described later.
The ADC 13 converts the analog signal outputted from the MUX 20 into a digital value. The FIR 14 performs band limitation and decimation processing on the signal having a digital value obtained by conversion of the ADC 13. The baseband signal having a digital value on which the band limitation and the decimation processing have been performed is transmitted to the MCU 19.
The MCU 19 performs arithmetic processing for obtaining radar information such as a distance to the target, a relative speed of the target, and an azimuth of the target, with use of the baseband signal outputted from the baseband circuit 18. This arithmetic processing is performed by the FET 15.
Next, operation modes of the radar device 100 according to the embodiment will be described. The radar device 100 according to the embodiment has a long range mode and a short range mode. The long range mode is a mode for detecting a target situated at a relatively long distance. The short range mode is a mode for detecting a target situated at a relatively short distance. Note that hereinafter, the long range mode may be referred to as a “first mode”, and the short range mode may be referred to as a “second mode” case by case. Also, target detection processing in the first mode may be referred to as “first detection processing”, and target detection processing in the second mode may be referred to as “second detection processing”. Note that, although details will be described later, the ADC 13 operates at a relatively low speed in the long range mode and operates at a relatively high speed in the short range mode.
Next, the configuration, connection, and function of the MUX 20 will be described.
Each MUX 20 includes two input terminals 20a and 20b and one output terminal 20c. In
In the baseband circuit 18, the input terminal 20a of the MUX 201 is connected to an output terminal of the BPF 121, and the input terminal 20b of the MUX 201 is connected to an output terminal of the BPF 123. The input terminal 20a of the MUX 202 is connected to an output terminal of the BPF 122, and the input terminal 20b of the MUX 202 is connected to an output terminal of the BPF 124. The input terminal 20a of the MUX 203 is connected to an output terminal of the BPF 12s, and the input terminal 20b of the MUX 203 is connected to an output terminal of the BPF 127. The input terminal 20a of the MUX 204 is connected to an output terminal of the BPF 126, and the input terminal 20b of the MUX 204 is connected to an output terminal of the BPF 123. That is, signals outputted from the BPF 123 and the BPF 122 are crossly inputted to the input terminal 20b of the MUX 201 and the input terminal 20a of the MUX 202, respectively in contradiction to component elements in respect of their layout. Likewise, signals outputted from the BPF 127 and the BPF 126 are crossly inputted to the input terminal 20b of the MUX 203 and the input terminal 20a of the MUX 204, respectively in contradiction to component elements in respect of their layout.
The MUX 20 has a function of sequentially switching and multiplexing two signals having passed through the BPFs 12 and outputting a signal obtained by the multiplexing to the ADC 13. As a result, by the switching operation of the MUXs 20, one of the input terminals 20a and 20b of each of the MUXs 20 receives, as its input, an output signal from any one of the receiving antennas adjacent to the receiving antenna in one-to-one correspondence with the receiving antennas 11 to 18 in respect of layout. Therefore, the number of the ADCs 13 need only be equal to that of the MUXs 20 and thus half the number of receiving channels. Note that hereinafter, the input terminal 20a may be referred to as a “first input terminal”, and the input terminal 20b may be referred to as a “second input terminal” case by case.
Note that the number of receiving channels is eight in
In the ROM 85, there are stored programs for various processings and databases referred to in the various processings. The programs and the databases may be recorded in a readable and writable recording medium other than the ROM 85. The recording medium may be any of a hard disk device, a portable recording medium including a CD-ROM, a DVD disk, and a USB memory, or a flash memory that is a semiconductor memory.
The programs are loaded to the RAM 84. The CPU 82 expands the programs in the program storage area in the RAM 84 and executes various processings by sending and receiving necessary information via the input/output unit 83. The data storage area in the RAM 84 serves as a work area used in execution of the various processings. The function of the MCU 19 described above and the function of the MCU 19 described later are implemented using the CPU 82.
Next, the operations in the short range mode and the long range mode of the embodiment will be described with reference to
As described above, the radar device 100 illustrated in
According to the above embodiment, the number of the receiving antennas that contribute to the first detection processing in the long range mode is larger than the number of the receiving antennas that contribute to the second detection processing in the short range mode. In addition, all the receiving antennas 1 belonging to the receiving array 16a contribute to the first detection processing, whereas some of the receiving antennas 1 belonging to the receiving array 16a contribute to the second detection processing. Moreover, the receiving antennas 1 that contribute to the second detection processing are adjacent to each other in the receiving array 16a.
As illustrated in
Moreover, in
When the radar device 100 operates in the long range mode, the MUX 201 switches between the receiving ch. 1 and the receiving ch. 3. Similarly, the MUX 202 switches between the receiving ch. 2 and the receiving ch. 4, the MUX 203 switches between the receiving ch. 5 and the receiving ch. 7, and the MUX 204 switches between the receiving ch. 6 and the receiving ch. 8. In each MUX 20, switching between the two receiving channels is performed at the same speed as a sampling frequency of the ADC 13. That is, in the MUX 20, the terminal through which a signal input is passed is alternately switched in a sampling period that is a reciprocal of the sampling frequency.
The ADC 13 always performs sampling at the same sampling frequency “fs” regardless of whether the operation is in the short range mode or the long range mode. Here, in the short range mode, data sampled by the ADC 13 is transferred to the FIR 14 corresponding to the channel number of the channel on which the data is acquired. In the case of data on the receiving ch. 3, the data acquired by the ADC 131 is transferred to the FIR 143. The same manner applies to the other receiving channels.
In the long range mode, the signal input to the MUX 20 is switched with a sampling period, and received data is multiplexed by the MUX 20 and then sampled by the ADC 13. The data sampled by the ADC 13 is distributed to the FIR 14 corresponding to the channel number. In the case of data on the receiving ch. 1 and the receiving ch. 3, the data is acquired by the ADC 131 and then distributed to the FIR 141 and the FIR 143.
Conventionally, the ADC has been provided for each receiving channel because design has not been made in consideration of natures of the short range mode and the long range mode. On the other hand, in the present embodiment, design is made in consideration of differences between the short range mode and the long range mode. Therefore, as illustrated in
Next, implementation ideas of the radar device 100 according to the embodiment will be described with reference to
As described above, in the long range mode, the through terminal of the MUX 20 is alternately switched with a sampling period of the ADC 13. On the other hand, in the short range mode, the signal input is fixed to one receiving channel. Therefore, as illustrated in
Furthermore, due to the switching operation of the MUX 20, in the long range mode, the data acquisition timing of the ADC 13 is shifted by a sampling period between the multiplexed receiving channels as shown by the waveforms on the right side of
(1) MCU Correction During Radar Signal Processing
Arithmetic processing for obtaining radar information such as a distance to a target, a relative speed of the target, and an azimuth of the target is performed by the FFT 15. Here, in the long range mode, as described above, the switching operation of the MUX 20 causes the timing shift by a sampling period between the FFT 151 and the FFT 153. Such a timing shift similarly occurs between the FFT 152 and the FFT 154, between the FFT 155 and the FFT 157, and between the FFT 156 and the FFT 158. Here, a phase difference due to this timing shift is referred to as a “reception phase difference” and is represented by “Δθfs”. The FFT 15 performs correction processing of canceling the reception phase difference Δθfs caused between the multiplexed receiving channels in a back calculation manner. This correction processing can be performed on an outcome of the FFT processing. Note that, in the short range mode, the switching operation of the MUX 20 is not performed, so that the correction of the reception phase difference Δθfs is unnecessary.
(2) FIR Correction after Acquisition of ADC Data As described above, in the long range mode, the reception phase difference Δθfs due to the switching operation of the MUX 20 occurs. Such a reception phase difference Δθfs also occurs between the FIR 141 and the FIR 143, between the FIR 142 and the FIR 144, between the FIR 145 and the FIR 147, and between the FIR 146 and the FIR 148. The FIR 14 has a property that the signal phase is shifted by half a period of the FIR output rate when compared between a case where the number of taps is an odd number and a case where the number of taps is an even number. Therefore, in the long range mode, if the number of taps is individually set to an odd number and an even number between the multiplexed receiving channels, then the reception phase difference Δθfs can be canceled. Specifically, the number of taps is individually set to an odd number and an even number between the FIR 141 and the FIR 143. Note that it goes without saying that a difference between the odd number and the even number in this example is one. The same applies to the relationship between the FIR 142 and the FIR 144, between the FIR 145 and the FIR 147, and between the FIR 146 and the FIR 143. Note that in the short range mode, all the FIRs 14 are communized to have one and the same number in the number of taps thereof. With this setting, correction of the reception phase difference Δθfs is not carried out.
As described above, the radar device according to the embodiment has the first mode for detecting a target at a relatively long distance and the second mode for detecting a target at a relatively short distance. The receiving channels, the number of which is a number obtained by multiplying a natural number by four, are configured in the antenna unit, the high frequency circuit, and the baseband circuit. Then, the number of receiving channels that is the number of receiving channels on which the conversion processing to the baseband signal is performed is smaller in the second mode than in the first mode, and the speed of the conversion processing is faster in the second mode than in the first mode. Such a configuration can prevent an increase in the number of the ADCs even when the number of receiving channels increases. As a result, an increase in size, manufacturing cost, and power consumption of the radar device can be prevented.
Note that the configuration illustrated in the aforementioned embodiment illustrates just an example, which can be combined with other publicly known techniques and partially omitted and/or modified without departing from the scope of the present disclosure.
1, 11 to 18 receiving antenna; 2, 21, 22 transmitting antenna; 3, 31 to 38 LNA; 4, 41 to 48 MIX; 5, 51 to 58 IFA; 6, 61, 62 PA; 7 VCO; 8 LF; 9 PLL; 10 chirp signal generator; 11, 111 to lie BBA; 12, 121 to 128 BPF; 13, 131 to 134 ADC; 14, 141 to 148 FIR; 15, 151 to 158 FFT; 16 antenna unit; 16a receiving array; 16b transmitting array; 17 high frequency circuit; 17a local unit; 18 baseband circuit; 19 MCU; 20, 201 to 204 MUX; 20a, 20b input terminal; 20c output terminal; 21 reference signal source; 80 computer; 82 CPU; 83 input/output unit; 84 RAM; 85 ROM; 100 radar device.
Number | Date | Country | Kind |
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2020-071291 | Apr 2020 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2021/001708 | 1/19/2021 | WO |