CN118131137A - Zero intermediate frequency circuit based on SFC technology - Google Patents
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Abstract
The invention discloses a zero intermediate frequency circuit based on SFC technology, which divides radio frequency signals into 2 paths through a two-way power divider after declinizing mixing, mixes the radio frequency signals with mutually orthogonal local oscillation signals to zero intermediate frequency respectively, filters SI signals through SFC (sensitivity frequency control) filtering, and sends the signals into an ADC for A/D conversion treatment. In order to ensure that various LFMCW waveform systems can be adopted to effectively filter SI interference signals, a program-controlled delay circuit is arranged at the input end of the declivity local oscillation signal, different delay amounts are arranged aiming at different modulation slopes of various waveforms, and the SI signal frequency spectrum is moved to the optimal inhibition position of the SFC filter by adjusting the starting moment of the declivity local oscillation signal. The invention has simpler architecture and easier realization of software and hardware; the filtering effect on SI interference signals is more obvious, and the elimination ratio can reach more than 30 dBc.
Description
Technical Field
The invention relates to the technical field of radio, in particular to a zero intermediate frequency circuit based on SFC technology.
Background
Frequency modulated continuous wave (Frequency Modulated ContinuousWave, FMCW) radar is one of many radar types, and if the modulated signal is linear, it may be referred to as a chirped continuous wave (LFMCW) radar. The LFMCW radar transmitting signal is frequency modulation continuous wave, has the advantages of simple structure, low peak power, strong anti-interference capability, small distance blind area and the like, and is widely applied in the fields of automobile anti-collision, material level measurement, traffic control, proximity fuze, altimeter and the like.
LFMCW radar transmits a simultaneous received signal, so that a transmission leakage signal enters the receiver simultaneously with an echo signal, and the effect of this transmission leakage signal on the receiver is called Self-interference (SI), the interference principle of which is shown in fig. 1.
The existence of SI seriously affects the performance of LFMCW radar, and in order to inhibit SI, the isolation of the transceiver antenna needs to be greatly improved so as to reduce the influence of interference on the sensitivity of the receiver. However, the isolation of the receiving and transmitting antenna is difficult to be high in a small baseline, and sometimes a cancellation method is needed, but the radio frequency cancellation technology is difficult to be applied in a high frequency band, and meanwhile, due to the characteristics of multipath, time variation and the like of SI signals, the real-time cancellation effect is not ideal, which seriously affects the performances of LFMCW radar such as the acting distance and the like. Therefore, a new method is needed to effectively eliminate SI interference signals.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention provides the SFC-based zero intermediate frequency circuit which is simple to realize and realizes the function of eliminating SI by utilizing the characteristics of the linear frequency modulation continuous wave signal and through conventional frequency mixing, filtering and other treatments.
The aim of the invention is achieved by the following technical scheme.
A zero intermediate frequency circuit based on SFC technology, comprising:
The device comprises a declivity mixer, a two-power divider, a VCO oscillator, an SFC filter and a program-controlled delay circuit; the radio frequency signal comprises an SI signal and a target echo signal, the radio frequency signal is divided into 2 paths through a two-way power divider after being declinized and mixed with mutually orthogonal local oscillation signals to zero intermediate frequency, the signals are filtered through an SFC filter, the SI signal is filtered and then sent to an ADC for A/D conversion treatment, a program-controlled delay circuit is arranged at the input end of the declinized local oscillation signal, different delay amounts are arranged aiming at different modulation slopes of various waveforms, and the SI signal frequency spectrum is moved to the optimal suppression position of the SFC filter by adjusting the starting moment of the declinized local oscillation signal.
The declivity processing of the target echo signal is as follows: assume that a certain LFMCW system transmits a linear frequency modulation signal as
Wherein B is bandwidth, T is time width, f 0 is radio frequency center frequency, and A 1 is amplitude;
The received signal is:
in/> For the echo distance delay of point target,/>Is the echo signal amplitude;
the SI interference signal is:
in/> For SI interference signal delay,/>The SI interference signal amplitude;
Declivity local oscillation signal is
In/>Is the center frequency of the linear frequency modulation local oscillation signal,Delay for declivity local oscillation;
Therefore, the deskew signal is:
；
；
；
and (3) calculating: Is the signal after the echo signal is declivated,/> Is the local oscillation amplitude,/>Is of intermediate frequency,/>Is the signal/>Complex conjugate of/>The phase angle of the echo signal is related to the time delay;
In the same way, the processing method comprises the steps of, The signal is the signal after the SI interference signal is declivated;
And/> All are single carrier frequency signals, and can be effectively resolved in the frequency domain.
The quadrature down-conversion of the deskewed signal to zero intermediate frequency is processed as follows: the mixing local oscillation signal is: ; the output signal after mixing is: ; neglecting the combined frequency components,/> And/>Principal spectral components differ in frequency domain/>。
And filtering the SI interference signal by an SFC filter: the SFC filter comprises a Butterworth band-pass filter and a trap filter, wherein the center frequency of the Butterworth band-pass filter is zero frequency, and the band width isB is the frequency modulation bandwidth of LFMCW, T is the frequency modulation time width of LFMCW,/>For the farthest acting distance of the radar, c is the light speed, and the center frequency of the wave trap is zero frequency; after filtering, a baseband echo signal/> isobtainedThe SI signal is filtered out.
The frequency modulation slope of different FMCWs is adapted by a program-controlled delay circuit: generating residual frequency after declivityAnd modulation slope/>Relatedly, LFMCW frequency modulation slope/>The intermediate frequency after the declining of the SI signal is changed, and the delay amount/>, of the declining local oscillation signal is delayed by a program-controlled delay circuitAdjusting to eliminate frequency variation/>Delay time/>, of program-controlled delay circuitThereby making/>The filtering effect of the back-end SFC filter on the SI signal is guaranteed as a fixed value.
Compared with the prior art, the invention has the advantages that:
1. Compared with the prior method for eliminating SI interference signals by adopting cancellation (radio frequency cancellation, intermediate frequency cancellation and digital cancellation), the invention has simpler architecture and easier realization of software and hardware;
2. compared with the prior art, the method has more remarkable effect of filtering SI interference signals, and the elimination ratio can reach more than 30 dBc.
Drawings
Fig. 1 is a schematic diagram of SI principle.
Fig. 2 is a schematic block diagram of LFMCW radar deskewing.
Fig. 3 is a schematic circuit diagram of the present invention.
Detailed Description
The invention will now be described in detail with reference to the drawings and the accompanying specific examples.
As shown in fig. 3, after the radio frequency signal (including SI signal and target echo signal) is declinized and mixed, the radio frequency signal is divided into 2 paths by a two-way power divider, mixed with mutually orthogonal local oscillation signals to zero intermediate frequency respectively, filtered by SFC (sensitivity frequency control), the SI signal is filtered, and then sent to an ADC for a/D conversion processing. In order to ensure that various LFMCW waveform systems can be adopted to effectively filter SI interference signals, a program-controlled delay circuit is arranged at the input end of the declivity local oscillation signal, different delay amounts are arranged aiming at different modulation slopes of various waveforms, and the SI signal frequency spectrum is moved to the optimal inhibition position of the SFC filter by adjusting the starting moment of the declivity local oscillation signal.
The receiving demodulation process of the LFMCW radar mainly uses a de-slope processing method, the basic idea is to use a local oscillator with the same frequency change rate as the transmitted signal, perform beat processing with the echo signal and then perform FFT, and the output frequency has a linear relation with the distance of the echo (time-frequency conversion), and the de-slope processing principle is shown in figure 2. Theoretically, when the frequency difference between the output SI signal and the echo signal is larger than the resolution bandwidth of the FFT, the echo signal can be extracted under the interference background of time domain overlapping.
If the modulation period of the LFMCW radar transmitting signal is T, the modulation bandwidth is B, and the initial frequency is f 0, the instantaneous frequency of the signal is: Wherein/> The slope is modulated for the signal.
If the target distance is R and the light speed is c, the frequency difference between the target echo signal and the transmitting signal is. Because the SI signal is a signal which is leaked from the transmitting unit to the receiving channel, the transmission distance is negligible, so/>。
Then, the frequency difference between the target echo signal and the SI signal is: Such as the intermediate frequency echo signal and spectrogram of fig. 2.
In the LFMCW radar, because the SI signal and the echo signal are aliased in the time domain, the SI signal is difficult to be removed effectively, the invention provides a processing architecture according to the characteristics of the LFMCW radar, which comprises the following steps:
As shown in fig. 3 at ① - ②, the rf signal (including SI signal and target echo signal) is declived and mixed, the rf signal spectrum is compressed to a limited bandwidth, and then split into 2 paths by the two power splitters. The bandwidth and the slope of the declivity local oscillation signal are the same as those of the transmitting signal, and the initial moment is related to the modulation slope, and the declivity local oscillation signal can be obtained by testing the system.
As shown in fig. 3 at ② - ③, the analog quadrature down-conversion is performed on the 2 paths of declinated rf signals, so that the spectrum of the rf signals is shifted to near zero frequency, i.e. to zero intermediate frequency. The analog quadrature down-conversion processing after the two power divisions is used for retaining the phase information of the signals and facilitating the realization of a back-end signal processing algorithm.
As shown in ③ - ⑤ in fig. 3, SFC filtering is performed on the 2 paths of zero intermediate frequency signals, so as to filter SI interference signals in the signals, and achieve the goal of eliminating SI influence and improving the performance of the receiving system.
The zero intermediate frequency circuit based on the SFC technology mainly comprises the following circuit modules: and the circuit modules comprise a declivity mixer, a two-power divider, a VCO oscillator, an SF filter and the like. The method mainly comprises the following steps:
Step one: and (5) declivity processing of the echo signals.
Assume that a certain LFMCW system transmits a linear frequency modulation signal as
Wherein B is bandwidth, T is time width, f 0 is radio frequency center frequency, and A 1 is amplitude;
The received signal is:
in/> For the echo distance delay of point target,/>Is the echo signal amplitude;
the SI interference signal is:
in/> For SI interference signal delay,/>The SI interference signal amplitude;
Declivity local oscillation signal is
In/>Is the center frequency of the linear frequency modulation local oscillation signal,Delay for declivity local oscillation;
Therefore, the deskew signal is:
；
；
；
and (3) calculating: Is the signal after the echo signal is declivated,/> Is the local oscillation amplitude,/>Is of intermediate frequency,/>Is the signal/>Complex conjugate of/>The phase angle of the echo signal is related to the time delay;
In the same way, the processing method comprises the steps of, The signal is the signal after the SI interference signal is declivated;
And/> All are single carrier frequency signals, and can be effectively resolved in the frequency domain.
Step two: quadrature down-conversion (to zero intermediate frequency) processing of the desked signal.
The mixing local oscillation signal is: ; the output signal after mixing is: /(I) ; The secondary parts such as the combined frequency components are ignored,And/>Principal spectral components differ in frequency domain/>。
Step three: and filtering the SI interference signal by an SFC filter.
The SFC filter comprises a Butterworth band-pass filter and a trap filter, wherein the center frequency of the Butterworth band-pass filter is zero frequency, and the band widthB is the frequency modulation bandwidth of LFMCW, T is the frequency modulation time width of LFMCW,/>For the farthest acting distance of the radar, c is the light speed, and the center frequency of the wave trap is zero frequency; after filtering, a baseband echo signal is obtainedThe SI signal is filtered out.
Step four: the frequency modulation slope of different FMCWs is adapted by a programmable delay circuit.
Because the initial moments of the deskew local oscillation signal and the SI signal have difference values, residual frequency is generated after deskewingAnd modulation slope/>Relatedly, LFMCW frequency modulation slope/>The intermediate frequency after the declining of the SI signal is changed, and the delay amount/>, of the declining local oscillation signal is delayed by a program-controlled delay circuitAdjusting to eliminate frequency variation/>Delay time/>, of program-controlled delay circuitThereby making/>The filtering effect of the back-end SFC filter on the SI signal is guaranteed as a fixed value.
The specific embodiments described herein are offered by way of example only to illustrate the spirit of the invention. Various modifications, additions, or substitutions to the described embodiments may be made by those skilled in the art without departing from the spirit of the invention or exceeding the scope of the invention as defined in the accompanying claims.
Claims (5)
1. The zero intermediate frequency circuit based on SFC technology is characterized by comprising:
The device comprises a declivity mixer, a two-power divider, a VCO oscillator, an SFC filter and a program-controlled delay circuit; the radio frequency signal comprises an SI signal and a target echo signal, the radio frequency signal is divided into 2 paths through a two-way power divider after being declinized and mixed with mutually orthogonal local oscillation signals to zero intermediate frequency, the signals are filtered through an SFC filter, the SI signal is filtered and then sent to an ADC for A/D conversion treatment, a program-controlled delay circuit is arranged at the input end of the declinized local oscillation signal, different delay amounts are arranged aiming at different modulation slopes of various waveforms, and the SI signal frequency spectrum is moved to the optimal suppression position of the SFC filter by adjusting the starting moment of the declinized local oscillation signal.
2. The zero intermediate frequency circuit based on the SFC technology as claimed in claim 1, wherein the deskewing process of the target echo signal is as follows: assume that a certain LFMCW system transmits a linear frequency modulation signal as
Wherein B is bandwidth, T is time width, f 0 is radio frequency center frequency, and A 1 is amplitude;
The received signal is:
in/> For the echo distance delay of point target,/>Is the echo signal amplitude;
the SI interference signal is:
in/> For SI interference signal delay,/>The SI interference signal amplitude;
Declivity local oscillation signal is
In/>Is the center frequency of the linear frequency modulation local oscillation signal,/>Delay for declivity local oscillation;
Therefore, the deskew signal is:
；
；
；
and (3) calculating: Is the signal after the echo signal is declivated,/> Is the local oscillation amplitude,/>Is of intermediate frequency,/>Is the signal/>Complex conjugate of/>The phase angle of the echo signal is related to the time delay;
In the same way, the processing method comprises the steps of, The signal is the signal after the SI interference signal is declivated;
And/> All are single carrier frequency signals, and can be effectively resolved in the frequency domain.
3. The zero intermediate frequency circuit based on the SFC technology as claimed in claim 1, wherein the quadrature down-conversion of the declassified signal to zero intermediate frequency is performed by: the mixing local oscillation signal is: ; the output signal after mixing is: ; neglecting the combined frequency components,/> And/>Principal spectral components differ in frequency domain/>。
4. The zero intermediate frequency circuit based on the SFC technology as claimed in claim 1, wherein the SI interference signal is filtered by the SFC filter: the SFC filter comprises a Butterworth band-pass filter and a trap filter, wherein the center frequency of the Butterworth band-pass filter is zero frequency, and the band width isB is the frequency modulation bandwidth of LFMCW, T is the frequency modulation time width of LFMCW,For the farthest acting distance of the radar, c is the light speed, and the center frequency of the wave trap is zero frequency; after filtering, a baseband echo signal is obtainedThe SI signal is filtered out.
5. The zero intermediate frequency circuit based on the SFC technology as claimed in claim 1, wherein the frequency modulation slope of different FMCWs is adapted by a programmable delay circuit: generating residual frequency after declivityAnd modulation slope/>Relatedly, LFMCW frequency modulation slope/>The intermediate frequency after the declining of the SI signal is changed, and the delay amount/>, of the declining local oscillation signal is delayed by a program-controlled delay circuitAdjusting to eliminate frequency variation/>Delay time/>, of program-controlled delay circuitThereby making/>The filtering effect of the back-end SFC filter on the SI signal is guaranteed as a fixed value.
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5091921A (en) * | 1989-04-20 | 1992-02-25 | Nec Corporation | Direct conversion receiver with dithering local carrier frequency for detecting transmitted carrier frequency |
| CA2522831A1 (en) * | 1995-03-09 | 1996-09-19 | Ericsson Inc. | Slope, drift and offset compensation in zero-if receivers |
| CN104113352A (en) * | 2014-07-22 | 2014-10-22 | 中国科学技术大学 | Transformer with self interference signal offsetting function and ultrahigh frequency radio frequency identification device (RFID) receiver front end based on same |
| CN105359408A (en) * | 2013-03-15 | 2016-02-24 | 多康公司 | Logarithmic amplifier with universal demodulation capabilities |
| CN111880169A (en) * | 2019-05-03 | 2020-11-03 | 恩智浦有限公司 | Radar sensing |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5091921A (en) * | 1989-04-20 | 1992-02-25 | Nec Corporation | Direct conversion receiver with dithering local carrier frequency for detecting transmitted carrier frequency |
| CA2522831A1 (en) * | 1995-03-09 | 1996-09-19 | Ericsson Inc. | Slope, drift and offset compensation in zero-if receivers |
| CN105359408A (en) * | 2013-03-15 | 2016-02-24 | 多康公司 | Logarithmic amplifier with universal demodulation capabilities |
| CN104113352A (en) * | 2014-07-22 | 2014-10-22 | 中国科学技术大学 | Transformer with self interference signal offsetting function and ultrahigh frequency radio frequency identification device (RFID) receiver front end based on same |
| CN111880169A (en) * | 2019-05-03 | 2020-11-03 | 恩智浦有限公司 | Radar sensing |
Non-Patent Citations (1)
| Title |
|---|
| 何方勇等: "无源 RFID 系统发射自干扰对消技术研究", "现代雷达", vol. 35, no. 5, 31 May 2013 (2013-05-31), pages 67 - 75 * |
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