System and method for calibration and built-in self test of automobile radar system

1. An inphase/quadrature (I/Q) mixer for a radar system, comprising:

a radio frequency (RF) input for receiving an RF signal;

a local oscillator (LO) input for receiving a LO signal;

a first stage of phase shitting circuitry for receiving the LO signal and applying a selectable phase shift to the LO signal to produce a first phase-shifted version of the LO signal;

a first set of switches being controllable to route the LO signal through the first stage of phase shifting circuitry to selectively apply the selectable phase shift to the LO signal according to states of the first set of switches, to produce the first phase-shifted version of the LO signal;

a first mixer unit receiving the RF signal at a first input of the first mixer unit;

a second mixer unit receiving the RF signal at a first input of the second mixer unit;

a second stage of phase shifting circuitry for receiving the first phase-shifted version of the LO signal, spitting the first phase-shifted version of the LO signal into a pair of split signals, and applying second and third phase shifts to the pair of split signals, respectively, to produce a pair of second phase-shifted versions of the LO signal, such that the pair of second phase-shifted versions of the LO signal are in quadrature;

a second set of switches being controllable to apply one of the pair of second phase-shifted versions of the LO signal to one of a second input of the first mixer unit and a second input of the second mixer unit and to apply the other of the pair of second phase-shifted versions of the LO signal to the other of the second input of the first mixer unit and the second input of the second mixer unit according to states of the second set of switches; and

a two-bit binary counter for generating a two-bit binary count in sequence, a most-significant bit (MSB) of the two-bit binary count being applied to the first set of switches to control the states of the first set of switches and a least-significant bit (LSB) of the two-bit binary count being applied to the second set of switches to control the states of the second set of switches, the two-bit binary count sequencing through the states of the first and second sets of switches as the two-bit binary count is generated in sequence.

2. The I/Q mixer of claim 1 , wherein the I/Q mixer is part of a homodyne radar system.

3. The I/Q mixer of claim 1 , wherein the first stage of phase shifting circuitry comprises two fixed phase shifters, one of which provides 0 degrees of phase shift and another of which provides 180 degrees of phase shift.

4. The I/Q mixer of claim 3 , wherein the first set of switches is controllable by the MSB to selectively apply phase shift of one of the two fixed phase shifters to the LO signal.

5. The I/Q mixer of claim 1 , wherein the second stage of phase shifting circuitry comprises an I/Q phase shifter which selectively provides 45 degrees of lead phase shift and 45 degrees of lag phase shift to generate the pair of second phase-shifted versions of the LO signal in quadrature.

6. The I/Q mixer of claim 5 , wherein the second set of switches is controllable by the LSB to selectively apply the lead or lag phase shift.

7. The I/Q mixer of claim 1 , wherein the I/Q mixer is a built-in self-test (BIST) element of the radar system.

8. The I/Q mixer of claim 1 , wherein sequencing through the states of the first and second sets of switches introduces a synthetic Doppler shift into the pair of second phase-shifted versions of the LO signal.

9. The I/Q mixer of claim 8 , wherein the synthetic Doppler shift is used to detect errors in the radar system.

10. The I/Q mixer of claim 9 , wherein the errors include leakage between transmit and receive circuits of the radar system.

11. The I/Q mixer of claim 9 , wherein the detected errors are used to calibrate the radar system.

12. A signal processing method in a radar system, the method comprising:

receiving a radio frequency (RF) signal at an RF input;

receiving a local oscillator (LO) signal and a LO input;

applying the LO signal to a first stage of phase shifting circuitry to apply a selectable phase shift to the LO signal to produce a first phase-shifted version of the LO signal;

controlling a first set of switches to selectively apply the selectable phase shift to the LO signal according to states of the first set of switches, to produce the first phase-shifted version of the LO signal;

receiving the RF signal at a first input of a first mixer unit;

receiving the RF signal at a first input of a second mixer unit;

applying the first phase-shifted version of the LO signal to a second stage of phase shifting circuitry to lit the first phase-shifted version of the LO signal into a pr of split signals and to apply second and third phase shifts to the pair of split signals, respectively, to produce a pair of second phase-shifted versions of the LO signal, such that the pair of second phase-shifted versions of the LO signal are in quadrature;

controlling a second set of switches to apply one of the pair of second phase-shifted versions of the LO signal to one of a second input of the first mixer unit and a second input of the second mixer unit and to apply the other of the pair of second phase-shifted versions of the LO signal to the other of the second input of the first mixer unit and the second input of the second mixer unit according to states of the second set of switches; and

generating a two-bit binary count in sequence, a most-significant bit (MSB) of the two-bit binary count being applied to the first set of switches to control the states of the first set of switches and a least-significant bit (LSB) of the two-bit binary count being applied to the second set of switches to control the states of the second set of switches, the two-bit binary count sequencing through the states of the first and second sets of switches as the two-bit binary count is generated in sequence.

13. The method of claim 12 , wherein the first stage of phase shifting circuitry comprises two fixed phase shifters, one of which provides 0 degrees of phase shift and one of which provides 180 degrees of phase shift.

14. The method of claim 13 , wherein the first set of switches is controllable by the MSB to selectively apply phase shift of one of the two fixed phase shifters to the LO signal.

15. The method of claim 12 , wherein the second stage of phase shifting circuitry comprises an I/Q phase shifter which selectively provides 45 degrees of lead phase shift and 45 degrees of lag phase shift to generate the pair of second phase-shifted versions of the LO signal in quadrature.

16. The method of claim 15 , wherein the second set of switches is controllable by the LSB to selectively apply the lead or lag phase shift.

17. The method of claim 12 , wherein the radar system is a homodyne system.

18. The method of claim 12 , wherein:

the first mixer unit generates a first inphase output signal lour by mixing the RF signal and the one of the pair of second phase shifted versions of the LO signal received at the second input of the first mixer unit; and

the second mixer unit generates a first quadrature output signal Q OUT by mixing the RF signal and the other of the pair of second phase shifted versions of the LO signal received at the second input of the second mixer unit.

19. The method of claim 18 , further comprising using I OUT and Q OUT to correct for errors and leakage measurements to calibrate the radar system.

20. The method of claim 12 , wherein sequencing through the states of the first and second sets of switches introduces a synthetic Doppler shift into the pair of second phase-shifted versions of the LO signal.

21. The method of claim 20 , wherein the synthetic Doppler shift is used to detect errors in the radar system.

22. The method of claim 21 , wherein the errors include leakage between transmit and receive circuits of the radar system.

23. The method of claim 21 , wherein the detected errors are used to calibrate the radar system.