CN107728116B - Radar system and leakage signal cancellation circuit and method thereof - Google Patents
Radar system and leakage signal cancellation circuit and method thereof Download PDFInfo
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- CN107728116B CN107728116B CN201710824013.4A CN201710824013A CN107728116B CN 107728116 B CN107728116 B CN 107728116B CN 201710824013 A CN201710824013 A CN 201710824013A CN 107728116 B CN107728116 B CN 107728116B
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Abstract
The application discloses a radar system and a leakage signal cancellation circuit and method thereof. The leakage signal cancellation circuit comprises a plurality of current branches, wherein the plurality of current branches are respectively enabled under bit data control of a control code so as to generate output currents of current weights corresponding to the bit weights of the control code, the output currents provided by the plurality of current branches are all zero when envelope signals of frequency modulated continuous waves are smaller than a preset threshold value, the output currents provided by the plurality of current branches are superposed on intermediate frequency signals of a receiver when the envelope signals of the frequency modulated continuous waves are larger than the preset threshold value, and the sum of the output currents provided by the plurality of current branches forms compensation currents corresponding to the value of the control code, so that leakage signals of the frequency modulated continuous wave signals from the transmitter to the receiver are cancelled.
Description
Technical Field
The invention belongs to the radar technology, and particularly relates to a radar system and a leakage signal cancellation circuit and method thereof.
Background
Radars are electronic devices that use electromagnetic waves to detect physics. When the radar works, the radar transmits radio frequency signals and detects echoes reflected from an object, so that information such as the distance of the object can be judged. With the development of intelligent equipment, the application of small-sized radars in the civil field is more and more extensive. The millimeter wave radar system has the characteristics of quick response, high precision, all-weather work, high flexibility and the like, and is widely applied to the fields of obstacle avoidance, detection, intelligent cruise and the like. For example, vehicle-mounted radars have been widely used for various vehicles for alerting the distance to an obstacle.
One of the most common modulation methods for vehicle-mounted radar is to use a frequency modulated continuous wave signal. The distance and velocity information can be detected simultaneously by transmitting and receiving frequency modulated continuous wave signals. Because the transmitter and the receiver must work simultaneously, the radar frequency modulation continuous wave signal at the transmitting end inevitably leaks to the receiving end, and further generates a zero intermediate frequency or low intermediate frequency signal through frequency mixing. The leakage signal is generated near low frequencies, which directly interferes with the detection of close range objects, creating a radar close range blind spot. Furthermore, the leakage signal, if large in amplitude, will also reduce the linearity and noise figure of the receiving baseband circuitry, even saturating the baseband receiver. Therefore, how to cancel the leakage signal from the transmitter to the receiver becomes a key to improve the reception sensitivity and reduce the radar dead zone.
In the existing radar system, signal leakage from the transmitter to the receiver is suppressed by physically separating the transmitter and the receiver, or by increasing the isolation of the transmitting antenna from the receiving antenna. However, this leakage signal suppression method is based on physical separation, not only increasing the size of the radar system, but also reducing the strength of the leakage signal only to some extent.
Thus. Further miniaturization of the radar system and an improvement in the suppression effect of the leak signal are expected.
Disclosure of Invention
In view of the above, the present invention provides a leakage signal cancellation circuit for a radar system, in which a control code is used to preset the magnitude of a compensation current, and when an envelope signal of a frequency modulated continuous wave is greater than a predetermined threshold, the compensation current is superimposed on an intermediate frequency signal, so as to simplify the circuit structure and improve the accuracy of correction of a leakage signal, thereby improving the suppression effect of the leakage signal.
According to a first aspect of the present invention, there is provided a leakage signal cancellation circuit for a radar system, a receiver of the radar system including a mixer for mixing a reception signal with a frequency-modulated continuous wave to generate an intermediate frequency signal, the leakage signal cancellation circuit comprising: the current branches are respectively enabled under the bit data control of a control code so as to generate output currents of current weights corresponding to the bit weights of the control code, wherein when an envelope signal of the frequency modulated continuous wave is smaller than a preset threshold value, the output currents provided by the current branches are all zero, when the envelope signal of the frequency modulated continuous wave is larger than the preset threshold value, the output currents provided by the current branches are superposed on the intermediate frequency signal, and the sum of the output currents provided by the current branches forms a compensation current corresponding to the value of the control code, so that leakage signals of the frequency modulated continuous wave signal from a transmitter to a receiver are at least partially counteracted.
Preferably, the mixer includes a first output terminal and a second output terminal, the intermediate frequency signal is a differential signal provided between the first output terminal and the second output terminal, and the plurality of current branches respectively include: a first current source and a second current source for generating a constant current of a value corresponding to the current weight; a first transistor and a second transistor, the first current source being connected from a power supply terminal to the first output terminal and the second output terminal via the first transistor and the second transistor, respectively; and a third transistor and a fourth transistor, the second current source connecting the first output terminal and the second output terminal to ground via the third transistor and the fourth transistor, respectively, wherein, during operation, the first current source and the second current source are enabled or disabled according to bit data of the control code, the first transistor and the second transistor are always in a conducting state, and the third transistor and the fourth transistor are respectively conducted according to a first selection signal and a second selection signal which are complementary to each other.
Preferably, the value of the control code and the levels of the first selection signal and the second selection signal are set during a system debugging phase or during power-up.
Preferably, gates of the first transistor and the second transistor are connected to a constant bias voltage.
According to a second aspect of the present invention, there is provided a method for cancelling a leakage signal from a transmitter to a receiver in a radar system, the receiver mixing a reception signal with a frequency-modulated continuous wave to generate an intermediate frequency signal, the method comprising: adopting bit data of a control code to control a plurality of current branches, and respectively generating output currents of current weights corresponding to the bit weights of the control code in the plurality of current branches; and superposing the output currents provided by the current branches on the intermediate frequency signal, wherein when the envelope signal of the frequency modulated continuous wave is smaller than a predetermined threshold, the output currents provided by the current branches are all zero, and when the envelope signal of the frequency modulated continuous wave is larger than or equal to the predetermined threshold, the sum of the output currents provided by the current branches forms a compensation current corresponding to the value of the control code, so that the leakage signal is at least partially cancelled.
Preferably, the intermediate frequency signal is a differential signal provided between a first output terminal and a second output terminal of a mixer, and the step of generating the output currents in the plurality of current branches comprises: generating a constant current with a value corresponding to the current weight by using a first current source and a second current source; enabling or disabling the first current source and the second current source according to bit data of the control code; and controlling the output currents of the plurality of current branches according to the envelope signal of the frequency-modulated continuous wave.
Preferably, controlling the output currents of the plurality of current branches comprises: generating a first selection signal and a second selection signal which are complementary to each other according to an envelope signal of the frequency-modulated continuous wave; and adopting the first selection signal and the second selection signal to respectively control the on-off states of a first path and a second path, wherein the first path sequentially passes through the first current source, the first output end and the second current source, and the second path sequentially passes through the first current source, the second output end and the second current source, wherein when the envelope signal of the frequency modulated continuous wave is smaller than a predetermined threshold value, both the first path and the second path are off, and when the envelope signal of the frequency modulated continuous wave is larger than or equal to the predetermined threshold value, one of the first path and the second path is on and the other is off, so that the constant current is provided for one of the first output end and the second output end.
Preferably, the method further comprises the following steps: and setting the value of the control code and the levels of the first selection signal and the second selection signal in a system debugging stage or power-on.
Preferably, the step of setting the first selection signal and the second selection signal includes: separating a differential signal of the envelope signal into the first selection signal and the second selection signal.
Preferably, the method further comprises the following steps: and according to a preset complementary control signal, inverting the levels of the first selection signal and the second selection signal during separation.
According to a third aspect of the present invention, there is provided a radar system comprising: a transmitter for generating a transmission signal according to the frequency modulated continuous wave and transmitting an electromagnetic wave via a transmission antenna; and a receiver for receiving the reflected electromagnetic wave from the object via the receiving antenna to generate a received signal to acquire distance information of the object, the receiver comprising: a mixer for mixing the received signal with the frequency-modulated continuous wave to generate an intermediate frequency signal, and acquiring the distance information according to a frequency of the intermediate frequency signal; and the leakage signal cancellation circuit described above.
Preferably, the receiver further comprises a polarity selection circuit for separating a differential signal of the envelope signal of the frequency-modulated continuous wave into a first selection signal and a second selection signal, and inverting the levels of the first selection signal and the second selection signal at the time of separation according to a preset complementary control signal.
Preferably, the polarity selection circuit includes: a third input and a fourth input for receiving the envelope signal; a third output terminal and a fourth output terminal for providing the first selection signal and the second selection signal, respectively; the input ends of the fifth transistor and the sixth transistor are commonly connected to the third input end, and the output ends of the fifth transistor and the sixth transistor are respectively connected to the third output end and the fourth output end; and a seventh transistor and an eighth transistor having input terminals commonly connected to the fourth input terminal and output terminals respectively connected to the third output terminal and the fourth output terminal, wherein the complementary control signal controls on-states of the fifth to eighth transistors such that the sixth transistor and the seventh transistor are turned off when the fifth transistor and the eighth transistor are turned on, and the fifth transistor and the eighth transistor are turned off when the sixth transistor and the seventh transistor are turned on.
Preferably, the method further comprises the following steps: and the envelope signal generating circuit is connected to the output end of the power amplifier of the transmitter or the output end of the preamplifier of the receiver and is used for generating a corresponding envelope signal according to the frequency-modulated continuous wave.
Preferably, the envelope signal is obtained by using a phase-locked loop to lock the frequency and phase of the output signal and the frequency-modulated continuous wave, and using an internal control voltage to simulate the envelope of the frequency-modulated continuous wave.
According to the leakage signal cancellation circuit and the leakage signal cancellation method, the size of the compensation current is preset by adopting the control code, and when the envelope signal of the frequency modulated continuous wave is larger than the preset threshold value, the compensation current is superposed on the intermediate frequency signal, so that the leakage signal of the frequency modulated continuous wave signal from the transmitter to the receiver is cancelled. The offset circuit can simplify the circuit structure and improve the correction accuracy of the leakage signal, thereby improving the suppression effect of the leakage signal, improving the sensitivity of a receiver and removing a distance detection blind area caused by leakage.
In a preferred embodiment, complementary control signals are used to set the levels of the first and second selection signals, thereby setting the polarity of the compensation current. The leakage signal cancellation circuit sets the magnitude and polarity of a compensation current according to a test result in advance, the compensation current is superposed on the intermediate frequency signal, and the compensation current is opposite to the polarity of a leakage signal mixed in the intermediate frequency signal, and the amplitude is approximately equal, so that the accuracy of leakage signal correction can be further improved, and the suppression effect of the leakage signal is improved.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings,
fig. 1 shows a schematic block diagram of a radar system according to the prior art.
Fig. 2 shows a schematic block diagram of a receiver in a radar system according to the prior art.
Fig. 3 shows a schematic block diagram of a receiver in a radar system according to an embodiment of the invention.
Fig. 4 shows a schematic block diagram of an envelope signal generating circuit in a radar system according to an embodiment of the present invention.
Fig. 5 shows a schematic block diagram of a polarity selection circuit and a leakage signal cancellation circuit in a radar system according to an embodiment of the present invention.
Detailed Description
The invention will be described in more detail below with reference to the accompanying drawings. Like elements in the various figures are denoted by like reference numerals. For purposes of clarity, the various features in the drawings are not necessarily drawn to scale. Moreover, certain well-known elements may not be shown in the figures.
In the following description, numerous specific details of the invention, such as structure, materials, dimensions, processing techniques and techniques of the devices are described in order to provide a more thorough understanding of the invention. However, as will be understood by those skilled in the art, the present invention may be practiced without these specific details.
Fig. 1 shows a schematic block diagram of a radar system according to the prior art. Radar system 100 includes a transmitter 110 and a receiver 120. The transmitter 110 includes a frequency modulated continuous wave generation module 111, a voltage controlled oscillator 112, a power amplifier 113, and a transmit antenna 114. The receiver 120 includes a low noise amplifier 121, a mixer 122, a transimpedance amplifier 123, and a reception antenna 124.
In the transmitter 110, the fm continuous wave generating module 111 generates a control signal Vctrll whose frequency varies periodically with time. The vco 112 generates a continuous wave signal with a frequency periodically varying with time according to the control signal Vctrl. The power amplifier 113 amplifies the continuous wave signal and transmits an electromagnetic wave to an external object via the transmitting antenna 114.
In the receiver 120, the receiving antenna 124 receives a reflected electromagnetic wave from an object from the outside, thereby obtaining a received signal. The low noise amplifier 121 amplifies the received signal and mixes the amplified signal with the continuous wave signal in the mixer 122 to generate an intermediate frequency signal. The transimpedance amplifier 123 amplifies the intermediate frequency signal to obtain a sensing signal for characterizing the object distance.
The radar system 100 operates on the principle of obtaining distance information of an object by measuring the frequency of an intermediate frequency signal. For example, a higher frequency of the intermediate frequency signal indicates a greater distance from the object. And vice versa.
As shown in fig. 1, leakage paths for frequency modulated continuous wave signals include inter-antenna coupling and inter-chip coupling. Since the frequency response of the modules on the signal chain is not perfectly flat, the output amplitude of the frequency modulated continuous wave signal will vary with frequency variations, thus producing an envelope signal. The leaked fm continuous wave signal, after mixing, will produce an envelope leakage signal at the receive baseband. The envelope leakage signal will be amplified by the transimpedance amplifier 123. The receive baseband will typically equalize the signal strength of the transmitting objects at different distances using a high pass filter that attenuates the envelope leakage signal to some extent, but the leakage signal will still affect the dynamic range of the transimpedance amplifier 123 and even saturate the receive baseband circuitry.
Fig. 2 shows a schematic block diagram of a receiver in a radar system according to the prior art.
Fig. 2 shows a further improved receiver 220 on the basis of that shown in fig. 1. Receiver 220 includes a low noise amplifier 121, a mixer 122, a transimpedance amplifier 123, a high pass filter 125, a variable gain amplifier 126, and a receive antenna 124.
In the receiver 220, after the transimpedance amplifier 123 amplifies the intermediate frequency signal to obtain a sensing signal for characterizing the object distance, the high pass filter 125 is used to filter out the low frequency noise of the sensing signal. The variable gain amplifier 126 further amplifies the sensing signal. In the receiving circuit 220, the frequency modulated continuous wave leakage signal is passed through the mixer 122 to generate an envelope signal and amplified by the transimpedance amplifier 123, thereby forming a signal leakage from the transmitter to the receiver.
In the receiver 220 shown in fig. 2, the low-frequency component in the fm continuous wave leakage signal can be suppressed to some extent by using the high-pass filter 125. However, the above-described conventional leakage signal suppression method can only reduce the intensity of the leakage signal to some extent.
Fig. 3 shows a schematic block diagram of a receiver in a radar system according to an embodiment of the invention.
The receiver 320 includes a low noise amplifier 121, a mixer 122, a transimpedance amplifier 123, a high-pass filter 125, a variable gain amplifier 126, an envelope signal generating circuit 127, a polarity selecting circuit 128, a leakage signal canceling circuit 129, and a receiving antenna 124.
In the receiver 320, the receiving antenna 124 receives a reflected electromagnetic wave from an object from the outside, thereby obtaining a received signal. The low noise amplifier 121 amplifies the received signal and mixes the amplified signal with the continuous wave signal in the mixer 122 to generate an intermediate frequency signal. The envelope signal generating circuit 127 generates an envelope signal of a frequency-modulated continuous wave. The envelope signal is selected to have a compensation polarity via the polarity selection circuit 128 and then is superimposed with the intermediate frequency signal in the leakage signal cancellation circuit 129 to obtain a correction signal. The transimpedance amplifier 123 amplifies the correction signal to obtain a sensing signal for characterizing the object distance. The high pass filter 125 is used to filter out low frequency noise of the sensing signal. The variable gain amplifier 126 further amplifies the sensing signal.
In the receiver 320 shown in fig. 3, the low-frequency component in the fm continuous wave leakage signal can be suppressed to some extent by using the high-pass filter 125. Further, the amplitude of the leakage signal of the frequency modulated continuous wave can be further reduced by using the envelope signal generating circuit 127, the polarity selecting circuit 128, and the leakage signal canceling circuit 129.
In this embodiment, the envelope signal generating circuit 127 is provided as part of the receiver, for example at the output of the LO preamplifier circuit of the receiver. In an alternative embodiment, the envelope signal generating circuit 127 may be part of the transmitter, for example at the PA output of the transmitter.
Fig. 4 shows a schematic block diagram of an envelope signal generating circuit in a radar system according to an embodiment of the present invention. The envelope signal generating circuit 127 may detect an envelope signal of the frequency-modulated continuous wave. The envelope signal generation circuit 127 includes a phase frequency detector 1271, current sources 1272 and 1273, a low pass filter 1274, a voltage controlled oscillator 1275, an N-divider 1276, and an operational amplifier 1278.
The phase frequency detector 1271 receives the phase difference between the input signal REF and the feedback signal FB, converts it into a control signal to control the current values of the current sources 1272 and 1273, and thereby generates the error signal ERR. The error signal ERR is filtered by the low pass filter 1274 to form a control voltage for the vco 1275, thereby controlling the frequency of the output signal SO of the vco 1275.
The operational amplifier 1278 has a non-inverting input connected to the intermediate node of the low pass filter 1274 and the voltage controlled oscillator 1275 to receive the control voltage and an inverting input connected to the output to form a follower. The envelope signal is provided at the output of the operational amplifier 1278.
The N-divider 1276 is connected in a feedback loop between the voltage controlled oscillator 1275 and the phase frequency detector 1271 so that a feedback signal FB is generated from the output signal of the voltage controlled oscillator 1275 and provided to the phase frequency detector 1271.
During operation, the output voltage is maintained at a fixed phase difference from the input voltage while the frequency of the output signal is proportionally reflected to the frequency of the input signal. The input signal REF of the envelope signal generation circuit 127 is a frequency modulated continuous wave signal REF, and the output signal is an envelope signal ENV. The envelope signal ENV is frequency and phase locked to the frequency modulated continuous wave signal REF. Since the envelope of the millimeter wave signal varies with frequency, and the signal frequency is determined by the control voltage of the control VCO inside the phase locked loop, the envelope signal ENV of the frequency modulated continuous wave can be simulated by the control voltage.
Fig. 5 shows a schematic block diagram of a polarity selection circuit and a leakage signal cancellation circuit in a radar system according to an embodiment of the present invention. In this embodiment, envelope signal ENV is polarity selected by polarity selection circuit 128 before generating complementary select signals SEL1 and SEL2, which are provided to leakage signal cancellation circuit 129. The leakage signal canceling circuit 129 superimposes the compensation current corresponding to the envelope signal ENV on the intermediate frequency signal. In this embodiment, the intermediate frequency signal provided by the mixer 122 is a current signal.
The polarity selection circuit 128 includes P-type MOS transistors M1 to M4 connected between two input terminals and two output terminals in a differential form. Transistors M1 and M2 are connected in parallel, with the sources commonly connected to the first input. The transistors M3 and M4 are connected in parallel, with the sources commonly connected to the second input terminal. The drains of transistors M1 and M3 are commonly connected to a first output terminal, and the drains of transistors M2 and M4 are commonly connected to a second output terminal. Further, the transistors M1 and M4 are turned on and off under the control of the control signal S, and the transistors M2 and M3 are turned on and off under the control of the control signal SB. The control signals S and SB are a pair of complementary signals.
When the control signal S is high, the transistors M1 and M4 are turned on and the transistors M2 and M3 are turned off, thereby transmitting the envelope signal ENV from the input terminal to the output terminal in the original polarity, generating complementary selection signals SEL1 and SEL2 of the first polarity. When the control signal S is low, the transistors M1 and M4 are turned off and the transistors M2 and M3 are turned on, thereby transmitting the envelope signal ENV from the input terminal to the output terminal with the polarity reversed, generating complementary selection signals SEL1 and SEL2 of the second polarity.
The leakage signal cancellation circuit 129 is connected to an intermediate node between the mixer 122 and the transimpedance amplifier 123, and is configured to superimpose the intermediate frequency signal output from the mixer 122 with a compensation current corresponding to the envelope signal ENV. The leakage signal cancellation circuit 129 includes a plurality of current branches of different current weights, and only the first current branch will be described hereinafter. With the control code BC (i.e., binary digits) corresponding to the plurality of current branches, the current branch of the current weight corresponding to the bit weight of the control code BC can be gated.
The first current branch comprises current sources IS11 and IS12, and N-type MOS transistors M11, M12, M21 and M22. The current source IS11 IS connected from the supply terminal to the intermediate node of the mixer 122 and the transimpedance amplifier 123 via the parallel-connected transistors M11 and M21. Further, the intermediate node IS connected to ground via parallel-connected transistors M12 and M22 and a current source IS 12. The gates of transistors M11 and M21 are connected to the bias voltage Vbias, and thus are always in a conducting state. The gates of the transistors M12 and M22 are connected to the polarity selection circuit 128 to receive the selection signals SEL1 and SEL2, i.e., are in a conductive state when the envelope signal ENV is greater than a predetermined threshold.
In this embodiment, transistors M11, M12, M21, and M22 all operate in a switching mode. The envelope signal ENV serves as a switch control signal. The compensation currents of the current sources IS11 and IS12 are equal, and the current weights of the current branches depend on the current values of the compensation currents. For example, the current weights of the first current branch and the second current branch are 1 and 2, respectively, and then the compensation current of the first current branch is 1/2 of the compensation current of the second current branch.
During a debugging phase of the receiver 320 shown in fig. 3, or at power-up, the level of the control signal S and the value of the control code BC may be adjusted in advance and stored in the receiver 320 for adjusting the polarity and magnitude of the compensation current in an operating state.
In operation, if the envelope signal ENV is less than a predetermined threshold, the transistors M11 and M21 are turned on, and the transistors M12 and M22 are turned off. The current path from the node to ground via transistors M12 and M22 IS broken and the currents injected from current source IS11 to the node via transistors M11 and M21 cancel each other out, and therefore the compensation current generated by leakage signal cancellation circuit 129 IS zero. If the envelope signal ENV is equal to or greater than a predetermined threshold, the transistors M11 and M21 are turned on, one of the transistors M12 and M22 is turned on and the other is turned off. The current path from the node to ground via one of the transistors M12 and M22 IS conductive, and therefore, the currents injected from the current source IS11 to the node via the transistors M11 and M21 fail to cancel, thereby generating a compensation current corresponding to the output currents of the current sources IS11 and IS 12.
Further, bit data of the control code BC IS provided to the control terminals of the current sources IS11 and IS12 to enable the current sources in the current branches. As described above, the control code BC has a preset numerical value. Thus, the compensation current generated by leakage signal cancellation circuit 129 is the sum of the weights of the current sources enabled by all current branches enabled according to the control code. In the above working process, the magnitude of the compensation current is preset by using the control code BC. The compensation current of a value corresponding to the control code BC is superimposed on the intermediate frequency signal generated by the mixer 122 so that the envelope signal ENV and the leakage signal mixed in the intermediate frequency signal have opposite polarities and substantially equal amplitudes. Thus, the leakage signal mixed in the intermediate frequency signal can be cancelled out and removed by the superposition, thereby improving the suppression effect. Therefore, the compensation current can cancel the leakage signal detected at the output terminal of the transimpedance amplifier 123, and substantially eliminate the influence of the leakage signal on the dynamic range of the transimpedance amplifier.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
While embodiments in accordance with the invention have been described above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and their full scope and equivalents.
Claims (15)
1. A leakage signal cancellation circuit for a radar system, a receiver of the radar system including a mixer for mixing a received signal with a frequency modulated continuous wave to generate an intermediate frequency signal, the leakage signal cancellation circuit comprising:
a plurality of current branches respectively enabled under bit data control of a control code to generate output currents of current weights corresponding to the bit weights of the control code,
wherein when the envelope signal of the frequency modulated continuous wave is smaller than a predetermined threshold, the output currents provided by the plurality of current branches are all zero,
when the envelope signal of the frequency-modulated continuous wave is larger than a preset threshold value, the output currents provided by the plurality of current branches are superposed on the intermediate frequency signal, and the sum of the output currents provided by the plurality of current branches forms a compensation current corresponding to the value of the control code, so that the leakage signal of the frequency-modulated continuous wave signal from the transmitter to the receiver is at least partially counteracted.
2. The leakage signal cancellation circuit of claim 1, wherein the mixer includes a first output terminal and a second output terminal, the intermediate frequency signal is a differential signal provided between the first output terminal and the second output terminal, and the plurality of current branches respectively include:
a first current source and a second current source for generating a constant current of a value corresponding to the current weight;
a first transistor and a second transistor, the first current source being connected from a power supply terminal to the first output terminal and the second output terminal via the first transistor and the second transistor, respectively; and
third and fourth transistors, the second current source connecting the first and second output terminals to ground via the third and fourth transistors, respectively,
in operation, the first current source and the second current source are enabled or disabled according to bit data of the control code, the first transistor and the second transistor are always in a conducting state, and the third transistor and the fourth transistor are respectively conducted according to a first selection signal and a second selection signal which are complementary to each other.
3. The leakage signal cancellation circuit according to claim 2, wherein a value of the control code and levels of the first selection signal and the second selection signal are set at a system debugging stage or at power-up.
4. The leakage signal cancellation circuit of claim 2, wherein gates of the first and second transistors are connected to a constant bias voltage.
5. A method for canceling a leakage signal from a transmitter to a receiver in a radar system, the receiver mixing a received signal with a frequency modulated continuous wave to generate an intermediate frequency signal, the method comprising:
adopting bit data of a control code to control a plurality of current branches, and respectively generating output currents of current weights corresponding to the bit weights of the control code in the plurality of current branches; and
superimposing the output currents provided by the plurality of current branches onto the intermediate frequency signal,
wherein when the envelope signal of the frequency modulated continuous wave is smaller than a predetermined threshold, the output currents provided by the plurality of current branches are all zero,
when the envelope signal of the frequency-modulated continuous wave is larger than or equal to a preset threshold value, the sum of the output currents provided by the current branches forms a compensation current corresponding to the value of the control code, and therefore the leakage signal is at least partially cancelled.
6. The method of claim 5, wherein the intermediate frequency signal is a differential signal provided between a first output and a second output of a mixer, the step of generating the output currents in the plurality of current branches comprising:
generating a constant current with a value corresponding to the current weight by using a first current source and a second current source;
enabling or disabling the first current source and the second current source according to bit data of the control code;
and controlling the output currents of the plurality of current branches according to the envelope signal of the frequency-modulated continuous wave.
7. The method of claim 6, wherein controlling the output currents of the plurality of current branches comprises:
generating a first selection signal and a second selection signal which are complementary to each other according to an envelope signal of the frequency-modulated continuous wave; and
respectively controlling the on-off states of a first path and a second path by using the first selection signal and the second selection signal, wherein the first path sequentially passes through the first current source, the first output end and the second current source, the second path sequentially passes through the first current source, the second output end and the second current source,
wherein the first path and the second path are both disconnected when the envelope signal of the frequency modulated continuous wave is less than a predetermined threshold,
when the envelope signal of the frequency-modulated continuous wave is equal to or greater than a predetermined threshold, one of the first path and the second path is turned on and the other is turned off, thereby supplying the constant current to one of the first output terminal and the second output terminal.
8. The method of claim 7, further comprising:
and setting the value of the control code and the levels of the first selection signal and the second selection signal in a system debugging stage or power-on.
9. The method of claim 8, wherein setting the first selection signal and the second selection signal comprises: separating a differential signal of the envelope signal into the first selection signal and the second selection signal.
10. The method of claim 9, further comprising: and according to a preset complementary control signal, inverting the levels of the first selection signal and the second selection signal during separation.
11. A radar system, comprising:
a transmitter for generating a transmission signal according to the frequency modulated continuous wave and transmitting an electromagnetic wave via a transmission antenna; and
a receiver for receiving the reflected electromagnetic wave from the object via the receiving antenna to generate a receiving signal to acquire distance information of the object,
the receiver includes:
a mixer for mixing the received signal with the frequency-modulated continuous wave to generate an intermediate frequency signal, and acquiring the distance information according to a frequency of the intermediate frequency signal; and
the leakage signal cancellation circuit according to any one of claims 1 to 4.
12. The radar system according to claim 11, wherein the receiver further comprises a polarity selection circuit for separating a differential signal of the envelope signal of the frequency-modulated continuous wave into a first selection signal and a second selection signal, and inverting the levels of the first selection signal and the second selection signal upon separation according to a preset complementary control signal.
13. The radar system of claim 12, wherein the polarity selection circuit comprises:
a third input and a fourth input for receiving the envelope signal;
a third output terminal and a fourth output terminal for providing the first selection signal and the second selection signal, respectively;
the input ends of the fifth transistor and the sixth transistor are commonly connected to the third input end, and the output ends of the fifth transistor and the sixth transistor are respectively connected to the third output end and the fourth output end; and
a seventh transistor and an eighth transistor having input terminals commonly connected to the fourth input terminal and output terminals connected to the third output terminal and the fourth output terminal, respectively,
wherein the complementary control signals control the on-state of the fifth, sixth, seventh and eighth transistors such that the sixth transistor seventh transistor is off when the fifth and eighth transistors are on, and the fifth transistor eighth transistor is off when the sixth and seventh transistors are on.
14. The radar system of claim 12, further comprising:
and the envelope signal generating circuit is connected to the output end of the power amplifier of the transmitter or the output end of the preamplifier of the receiver and is used for generating a corresponding envelope signal according to the frequency-modulated continuous wave.
15. The radar system of claim 14, wherein the envelope signal is obtained by using a phase locked loop to achieve frequency and phase locking of an output signal with the frequency modulated continuous wave, and using an internal control voltage to simulate the envelope of the frequency modulated continuous wave.
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