FIELD OF THE INVENTION

The present disclosure is related to sensing technologies.

BACKGROUND

A radar system transmits a signal and receives its echo. By processing the echo signal, the radar system is able to detect objects, and to estimate the distances, velocities, and directions associated with the objects. Historically, a pulsed radar is used in military applications, where targets of interest are typically far away from the radar system. The pulsed radar emits short pulses, and in the silent period receives the echo signals. The transmitter of the pulsed radar system is turned off before the measurement starts. However, in many civilian applications, such as automotive radar, wireless gesture recognition, vital sign monitoring, and other monitoring implementations, the objects of interest are usually close to the radar. Due to the short round-trip-delay (RTD) of the desired reflection signal, a pulsed radar doesn't work as well at close range. Instead of a pulsed radar, a frequency-modulated continuous wave or waveform (FMCW) radar is used for short distances.

In FMCW radar, the transmission signal is modulated in frequency (or in phase) and differences in phase or frequency between the transmitted signal and a received signal are used to measure distance to the object from which the transmitted signal is reflected. A linear frequency modulated (LFM) waveform can be used, whose instantaneous frequency linearly increases or decreases over time. With the change in frequency being linear over a wide range, then the distance can be determined by a frequency comparison, with the frequency difference being proportional to the distance.

FIG. 1is a block diagram of a typical FMCW radar. A waveform generator102generates a radar probing waveform, such as a LFM waveform (i.e., chirp). The generated waveform is amplified by a power amplifier (PA)103, and then transmitted from the transmitter antenna104repeatedly and periodically. At the same time, the signal received by the receiver antenna114is first amplified by a low-noise amplifier (LNA)113, and then mixed at mixer106with a replica of the transmitted waveform. A low-pass filter (LPF)107and a digital-to-analog (ADC)112are then applied to the output of mixer106.

When LFM is used, the signal reflected from an object can be modeled as a sinusoid at the mixer output, whose frequency is proportional to the RTD. An ideal waveform for transmission in a FMCW radar can be taken to be a signal, s(t):
s(t)=ej2π(ƒct+0.5γt2),  (1)
with ƒcand γ being the center frequency for the waveform and the chirp rate, respectively. A chirp, which can be referred to as a sweep signal, is a signal in which the frequency increases or decreases with time. The chirp rate is the rate of change in the chirp. The instantaneous frequency for s(t) is given as ƒc+γt, linearly increasing over time t. The received signal, as a reflected signal from an object to which the transmitted signal is incident, can be modeled as x(y):
x(t)=βs(t−τ)=βej2π(ƒc(t−τ)+0.5γ(t−τ)2),(2)
with β and τ being amplitude and delay, respectively. The signals s(t) and x(t) can be combined at mixer106, for example, having output, y(t):
y(t)=x*(t)s(t)=βej2π(ƒcτ−0.5γτ2)ej2πτγtτ,  (3)
which is a sinusoid over t. By applying a fast Fourier transform (FFT) to the output of ADC112, for example, the object can be detected, the associated delay τ can be estimated, and an associated distance to the object can be generated.

In operation, a FMCW radar repeats transmission of the LFM waveform continuously or with a small gap between periods. Therefore, in FMCW radar, the transmitter and receiver operate concurrently. Because of this concurrent operation, the transmitted signal can leak into the receive channel from the transmitter (Tx) antenna to the receiver (Rx) antenna directly (without reflection), or even within the radio frequency (RF) circuit. This Tx-to-Rx leakage signal can be much stronger than the desired reflection signal, and can cause severe problems. First, it can generate “ghost” targets, which cause false detections. In such cases, the leakage signal acts as a representation that the transmitted probe had been reflected from an object. Since this is a detection of a leakage signal, the detected signal is not provided by an actual object, hence the detection is from a “ghost” target. Second, it can mask true targets, causing missing detection. Even worse, it can saturate components of the receiver, such as an analog-to-digital converter (ADC), and totally disable the radar system.

Therefore, it is a critical and challenging task to cancel or reduce the Tx-to-Rx leakage in FMCW radar or otherwise account for the Tx-to-Rx leakage. Many methods have been presented in the literature. Some methods perform the Tx-to-Rx leakage cancellation in the analog domain, whose performance is usually limited. A reported method performs leakage cancellation in the digital domain, which, however, cannot solve the receiver saturation problem. Some proposed methods consider a mixed leakage cancellation scheme, which estimates the leakage signal in the digital domain and cancels it in the analog domain. However, in such a mixed leakage cancellation scheme, the leakage cancelation step is carried out at radio frequency (RF) using additional mixers, which scheme increases the complexity and cost of a radar transceiver.

SUMMARY

A system and method comprise generating a leakage cancellation signal in the digital domain and cancelling a leakage signal in receiving a signal in the analog domain based on the leakage cancellation signal generated in the digital domain. A waveform generator generates a source signal for wireless transmission for detection in receive path circuitry of an ingoing signal that is a reflection of the transmitted signal from an object. Receive path circuitry, coupled to receive the ingoing signal corresponding to the transmitted source signal and to process the ingoing signal, include a mixer coupled to receive the source signal, the ingoing signal, and a leakage signal associated with the source signal, where the mixer produces a mixer output signal. An analog-to-digital converter is implemented to produce a digital mixer output signal that is based upon the mixer output signal. Subtraction circuitry is disposed electrically between the mixer and the analog-to-digital converter to subtract a leakage cancellation signal from the mixer output signal. The leakage cancellation is generated by digital processing circuitry that comprises a cancellation signal generator coupled to receive the digital mixer output signal to produce a digital cancellation signal. A digital to analog converter is coupled to receive the digital cancellation signal to produce the leakage cancellation signal.

Various examples are now described to introduce a selection of concepts in a simplified form that are further described below in the detailed description. The Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

According to one aspect of the present disclosure, there is provided a system comprising: a waveform generator to generate a source signal for wireless transmission from at least one antenna; receive path circuitry coupled to receive an ingoing radio frequency (RF) signal to process the ingoing RF signal, the receive path circuitry comprising: a mixer coupled to receive the source signal, the ingoing RF signal, and a leakage signal associated with the source signal, wherein the mixer produces a mixer output signal, an analog-to-digital converter that produces a digital mixer output signal that is based upon the mixer output signal, subtraction circuitry disposed electrically between the mixer and the analog-to-digital converter to subtract a leakage cancellation signal from the mixer output signal, and digital processing circuitry that comprises: a cancellation signal generator coupled to receive the digital mixer output signal to produce a digital cancellation signal, and a digital to analog converter coupled to receive the digital cancellation signal to produce the leakage cancellation signal.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the system includes a first switch coupled to receive the mixer output signal and coupled to the subtraction circuitry to provide the received mixer output signal to the subtraction circuitry, and a second switch coupled to receive the leakage cancellation signal and coupled to the subtraction circuitry to provide the received leakage cancellation signal to the subtraction circuitry, operation of the first and second switches coordinated to operate the subtraction circuitry in a working mode and in a calibration mode.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the system includes a variable gain amplifier coupled between the subtraction circuitry and the analog-to-digital converter, the variable gain amplifier adjustable such that, in the calibration mode, the variable gain amplifier is set to a low-gain relative to a gain setting of the variable gain amplifier in the working mode.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the cancellation signal generator includes access to a storage device to store the digital cancellation signal or parameters to generate the digital cancellation signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the cancellation signal generator includes circuitry to convert a calibration signal, without compensation for signal leakage, to a first frequency domain calibration signal, convert a delta function to a second frequency domain calibration signal, generate a frequency domain leakage cancellation signal from the first and second frequency domain calibration signals, and convert the frequency domain leakage cancellation signal to the digital cancellation signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides the system further comprising: residual leakage estimation circuitry coupled to receive the digital mixer output signal to produce a residual leakage estimation, second subtraction circuitry coupled to receive the digital mixer output and the residual leakage estimation to produce a radar output signal, and wherein the subtraction circuitry subtracts the residual leakage estimation from the digital mixer output to produce the radar output signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the residual leakage estimation circuitry includes the residual leakage estimation circuitry structured to generate a multiplicative factor from an average of the digital mixer output signal over time and to apply the multiplicative factor to the digital mixer output signal to generate the residual leakage estimation

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the system includes circuitry arranged to control a sensing function with respect to the generated source signal, based on the digital mixer output signal or the digital mixer output signal after reduction of a residual leakage estimation from the digital mixer output signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that components of the system are structured to include a frequency-modulated continuous wave radar.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides the system further comprising: one or more additional receive path circuitries identical to the receive path circuitry, one or more additional digital processing circuitries identical to the digital processing circuitry, each of the one or more additional receive path circuitries coupled to a respective one additional receive path circuitry of the additional receive path circuitries, and wherein the receive path circuitry and its associated digital processing circuitry and the one or more additional receive path circuitries and their associated one or more additional digital processing circuitries are structured to operate in parallel with respect the source signal generated by the waveform generator.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that each digital processing circuitry of the plurality digital processing circuitries comprises: residual leakage estimation circuitry coupled to receive a respective digital mixer output signal to produce a residual leakage estimation in the respective digital processing circuitry, second subtraction circuitry coupled to receive the respective digital mixer output and the residual leakage estimation to produce a radar output signal in the respective digital processing circuitry, and wherein the subtraction circuitry subtracts the residual leakage estimation from the respective digital mixer output to produce the radar output signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the system further comprises: the at least one antenna being a plurality of transmitter antennas, each transmitter antenna being selective in turn for transmission of a corresponding source signal derived from the waveform generator, a plurality of receiver antennas, each receiver antenna coupled to a respective one receive path circuitry of a plurality of receive path circuitries identical to and including the receive path circuitry, the plurality of receiver antennas and their coupled respective receive path circuitries structured to operate in parallel, and a plurality of digital processing circuitries, each digital processing circuitry coupled to a respective one receive path circuitry of the plurality of receive path circuitries, the digital processing circuitries identical to and including the digital processing circuitry, the cancellation signal generator of each digital processing circuitry to operate as a number of leakage cancellers operating serially with each leakage canceller corresponding to one of the transmitter antennas, each cancellation signal generator of each digital processing circuitry to operate in parallel with the other cancellation signal generator of the other digital processing circuitries.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that each digital processing circuitry of the plurality digital processing circuitries comprises: residual leakage estimation circuitry coupled to receive a respective digital mixer output signal corresponding to each transmitter antenna to produce a residual leakage estimation corresponding to each transmitter antenna in the respective digital processing circuitry, second subtraction circuitry coupled to receive the respective digital mixer output corresponding to each transmitter antenna and the residual leakage estimation corresponding to each transmitter antenna to produce a radar output signal corresponding to each transmitter antenna in the respective digital processing circuitry, and wherein the subtraction circuitry subtracts the residual leakage estimation from the respective digital mixer output to produce the radar output signal corresponding to each transmitter antenna.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the system further comprises: the at least one antenna being a plurality of transmitter antennas, each transmitter antenna being selective in turn for transmission of a corresponding source signal derived from the waveform generator, a plurality of receiver antennas, each receiver antenna selectively coupled to the receive path circuitry for signal reception in turn such that the each receiver antenna operates with each transmitter as a transmitter-receiver pair at selected times, and the cancellation signal generator of the digital processing circuitry to operate as a number of leakage cancellers operating serially with each leakage canceller corresponding to one transmitter-receiver pair of the transmitter-receiver pairs.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the system further comprises the residual leakage estimation circuitry to operate as a number of residual leakage estimators to receive a digital mixer output signal corresponding to each transmitter-receiver pair to produce a residual leakage estimation corresponding to each transmitter-receiver pair in the digital processing circuitry; the second subtraction circuitry coupled to receive the digital mixer output corresponding to each transmitter-receiver pair and the residual leakage estimation corresponding to each transmitter-receiver pair to produce a radar output signal corresponding to each transmitter-receiver pair in the digital processing circuitry; and wherein the subtraction circuitry subtracts the residual leakage estimation from the respective digital mixer output to produce the radar output signal corresponding to each transmitter-receiver pair.

According to one aspect of the present disclosure, there is provided a system comprising: a waveform generator to generate a source signal for acoustic transmission from at least one acoustic transmitter; receive path circuitry coupled to receive an ingoing signal to process the ingoing signal after conversion from an ingoing acoustic signal; the receive path circuitry comprising: a mixer coupled to receive the source signal; the ingoing signal; and a leakage signal associated with the source signal; wherein the mixer produces a mixer output signal; an analog-to-digital converter that produces a digital mixer output signal that is based upon the mixer output signal; subtraction circuitry disposed electrically between the mixer and the analog-to-digital converter to subtract a leakage cancellation signal from the mixer output signal; and digital processing circuitry that comprises: a cancellation signal generator coupled to receive the digital mixer output signal to produce a digital cancellation signal; and a digital to analog converter coupled to receive the digital cancellation signal to produce the leakage cancellation signal.

Optionally, in any of the preceding aspects; another implementation of the aspect provides that the system includes a first switch coupled to receive the mixer output signal and coupled to the subtraction circuitry to provide the received mixer output signal to the subtraction circuitry; and a second switch coupled to receive the leakage cancellation signal and coupled to the subtraction circuitry to provide the received leakage cancellation signal to the subtraction circuitry; operation of the first and second switches coordinated to operate the subtraction circuitry in a working mode and in a calibration mode.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the cancellation signal generator includes circuitry to convert a calibration signal, without compensation for signal leakage, to a first frequency domain calibration signal, convert a delta function to a second frequency domain calibration signal, generate a frequency domain leakage cancellation signal from the first and second frequency domain calibration signals, and convert the frequency domain leakage cancellation signal to the digital cancellation signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides the system further comprising: residual leakage estimation circuitry coupled to receive the digital mixer output signal to produce a residual leakage estimation, second subtraction circuitry coupled to receive the digital mixer output and the residual leakage estimation to produce a detection output signal, and wherein the subtraction circuitry subtracts the residual leakage estimation from the digital mixer output to produce the detection output signal.

According to one aspect of the present disclosure, there is provided a method comprising: generating a source signal for wireless transmission from at least one antenna, receiving an ingoing radio frequency (RF) signal and processing the ingoing RF signal, the processing comprising: mixing the source signal, the ingoing RF signal, and a leakage signal associated with the source signal, producing a mixer output signal, subtracting a leakage cancellation signal from the mixer output signal, and producing a digital mixer output signal that is based upon the mixer output signal, wherein production of the leakage cancellation signal comprises: producing a digital cancellation signal by a cancellation signal generator coupled to receive the digital mixer output signal; and converting the digital cancellation signal to an analog signal to produce the leakage cancellation signal.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that producing the digital cancellation signal includes converting a calibration signal, without compensating for signal leakage, to a first frequency domain calibration signal, converting a delta function to a second frequency domain calibration signal, generating a frequency domain leakage cancellation signal from the first and second frequency domain calibration signals; and converting the frequency domain leakage cancellation signal to the digital cancellation signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the method includes estimating a residual leakage signal based on the digital mixer output signal; and producing a radar output signal from subtracting the estimated residual leakage signal from the digital mixer output signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that estimating the residual leakage signal includes generating a multiplicative factor from averaging the digital mixer output signal over time and applying the multiplicative factor to the digital mixer output signal to generate the estimated residual leakage signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the method includes performing a sensing function with respect to the source signal based on the digital mixer output signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that performing the sensing function includes performing the sensing function as part of a frequency-modulated continuous wave radar.

