Frequency nonlinearity calibration in frequency-modulated continuous wave radar
Various embodiments include methods and systems having a frequency-modulated continuous wave radar operable to compensate a return signal for nonlinearity in the associated radar signal that is transmitted. The radar signal can be mixed with a delayed version of the radar signal such that the mixed signal can be used to generate an estimate of the nonlinearity. The estimate can be used to compensate the return signal from an object that reflects the associated transmitted radar signal. Additional apparatus, systems, and methods can be implemented in a variety of applications.
1. A system having a frequency-modulated continuous wave radar, the system comprising:
a waveform generator to generate a radar signal having an instantaneous frequency, the instantaneous frequency being linear plus a nonlinearity;
a transmitting antenna to transmit the radar signal;
a receiving antenna to receive a return signal from an object that reflects the transmitted radar signal;
a first mixer to mix the radar signal with the return signal and to output a first mixer output signal;
a first analog-to-digital converter to convert the first mixer output signal to a first digital mixer output signal;
a delay generator coupled to the waveform generator to generate a delayed radar signal;
a second mixer to mix the radar signal with the delayed radar signal and to output a second mixer output signal;
a second analog-to-digital converter to convert the second mixer output signal to a second digital mixer output signal; and
circuitry to generate an estimate of the nonlinearity based on the second digital mixer output signal and to compensate the first digital mixer output signal by use of the estimate.
2. The system of claim 1 , wherein the circuitry is arranged to generate the estimate as a function of time based on phase of the second digital mixer output signal, center frequency of the radar signal, chirp rate of the radar signal, and delay of the delayed radar signal.
3. The system of claim 1 , wherein the circuitry is arranged to record the first digital mixer output signal and to resample the first digital mixer output signal at an adjusted time using the estimate.
4. The system of claim 3 , wherein the circuitry to resample includes an interpolation of the first digital mixer output signal at sampled times immediately before and immediately after the adjusted time.
5. The system of claim 1 , wherein a delay of the delay generator to generate a delayed radar signal is in the range from 100 picoseconds to 10 nanoseconds.
6. The system of claim 1 , wherein the system includes a first low pass filter coupling the first mixer to the first analog-to-digital converter and a second low pass filter coupling the second mixer to the second analog-to-digital converter.
7. A system having a frequency-modulated continuous wave radar, the system comprising:
a waveform generator to generate a radar signal having an instantaneous frequency, the instantaneous frequency being linear plus a nonlinearity;
a transmitting antenna to transmit the radar signal;
a receiving antenna to receive a return signal from an object that reflects the transmitted radar signal;
a delay generator coupled to the waveform generator to generate a delayed radar signal;
a mixer coupled to the waveform generator to receive the radar signal;
a switch having an input coupled to the delay generator, an input coupled to a path to the receiving antenna, and an output coupled to the mixer such that with the switch operatively coupling the receiving antenna to the mixer, an output of the mixer provides a first mixer output signal from mixing the radar signal with the return signal, and with the switch operatively coupling the delay generator to the mixer, an output of the mixer provides a second mixer output signal from mixing the radar signal with the delayed radar signal;
an analog-to-digital converter coupled to the mixer to convert the first mixer output signal to a first digital mixer output signal and to convert the second mixer output signal to a second digital mixer output signal; and
circuitry to generate an estimate of the nonlinearity based on the second digital mixer output signal and to compensate the first digital mixer output signal by use of the estimate.
8. The system of claim 7 , wherein the circuitry is arranged to generate the estimate as a function of time based on phase of the second digital mixer output signal, center frequency of the radar signal, chirp rate of the radar signal, and delay of the delayed radar signal.
9. The system of claim 7 , wherein the circuitry is arranged to record the first digital mixer output signal and to resample the first digital mixer output signal at an adjusted time using the estimate.
10. The system of claim 7 , wherein the circuitry to resample includes an interpolation of the first digital mixer output signal at sampled times immediately before and immediately after the adjusted time.
11. The system of claim 7 , wherein delay of the delay generator to generate a delayed radar signal is in the range from 100 picoseconds to 10 nanoseconds.
12. The system of claim 7 , wherein the system includes a low pass filter coupling the mixer to the analog-to-digital converter.
13. A method of operating a frequency-modulated continuous wave radar, the method comprising:
generating, using a waveform generator, a radar signal having an instantaneous frequency, the instantaneous frequency being linear plus a nonlinearity;
transmitting the radar signal from a transmitting antenna;
receiving, at a receiving antenna, a return signal from an object that reflects the transmitted radar signal;
mixing the radar signal with the return signal and outputting a first mixer output signal;
converting the first mixer output signal to a first digital mixer output signal;
generating, using a delay generator, a delayed radar signal from the radar signal;
mixing the radar signal with the delayed radar signal and outputting a second mixer output signal;
converting the second mixer output signal to a second digital mixer output signal; and
generating an estimate of the nonlinearity based on the second digital mixer output signal and compensating the first digital mixer output signal using the estimate.
14. The method of claim 13 , wherein generating the estimate of the nonlinearity includes estimating the nonlinearity as a function of time based on phase of the second digital mixer output signal, center frequency of the radar signal, chirp rate of the radar signal, and delay of the delayed radar signal.
15. The method of claim 13 , wherein compensating the first digital mixer output signal includes recording the first digital mixer output signal and resampling the first digital mixer output signal at an adjusted time using the estimate.
16. The method of claim 15 , wherein resampling the first digital mixer output signal includes interpolating the first digital mixer output signal at sampled times immediately before and immediately after the adjusted time.
17. The method of claim 13 , wherein the method includes
operating a switch with a mixer that provides the first mixer output signal and the second mixer output signal in a calibration mode or in a compensation mode such that the calibration mode is executed with the switch operatively coupling the delay generator to the mixer, and the compensation mode is executed with the switch operatively coupling the mixer to the receiving antenna.
18. The method of claim 13 , wherein the method includes applying a fast Fourier transform to the compensated first digital mixer output signal to detect the object and to estimate a delay associated with transmitting the radar signal and receiving the return signal.
19. The method of claim 13 , wherein includes using the compensated first digital mixer output signal to determine one or more characteristics for the object from a set including distance, velocity, and direction associated with the object.
20. The method of claim 13 , wherein the method includes operating the frequency-modulated continuous wave radar in an automobile or a terminal device.