Automatic image rejection calibration for radar systems using quadrature transceivers

1. A frequency modulated continuous-wave (FMCW) radar system comprising:

a quadrature transceiver comprising:

a transmitter having an in-phase input and a quadrature input; and

a receiver having an in-phase output and a quadrature output;

a dual channel FMCW signal generator having two direct digital synthesizers (DDSs), comprising:

a first output coupled to the in-phase input of the transmitter; and

a second output coupled to the quadrature input of the transmitter;

a first splitter coupled between the first output of the dual channel FMCW signal generator and the in-phase input of the transmitter;

a second splitter coupled between the second output of the dual channel FMCW signal generator and the quadrature input of the transmitter;

a first mixer comprising:

a first input coupled to a second output of the first splitter;

a second input coupled to the in-phase output of the receiver; and

an output of the first mixer;

a second mixer comprising:

a first input coupled to a second output of the second splitter;

a second input coupled to the quadrature output of the receiver; and

an output of the second mixer;

a dual channel analog to digital converter (ADC) comprising:

a first input coupled to the output of the first mixer; and

a second input coupled to the output of the second mixer; and

a controller coupled between the dual channel FMCW signal generator and the dual channel ADC.

2. The FMCW radar system of claim 1 , wherein the dual channel FMCW signal generator is programmable.

3. The FMCW radar system of claim 1 , wherein the dual channel FMCW is configured to provide a windowing signal that indicates a start and an end of each frequency ramp cycle.

4. The FMCW radar system of claim 1 , wherein the controller comprises a quadrature calibration block that is configured to receive an in-phase beat signal from a first output of the dual channel ADC and a quadrature beat signal from a second output of the dual channel ADC.

5. The FMCW radar system of claim 4 , further comprising a low pass filter at each input channel of the dual channel ADC.

6. The FMCW radar system of claim 4 , wherein the controller further comprises a Fast Fourier Transform (FFT) block configured to receive the in-phase beat signal and the quadrature beat signal from the second output of the dual channel ADC and to provide a radar output having an improved signal to noise ratio (SNR).

7. The FMCW radar system of claim 4 , wherein the quadrature calibration block is configured to provide at least one of a phase calibration variable (θ t ) or an amplitude calibration variable (A t ) as input to the dual output FMCW signal generator.

8. The FMCW radar system of claim 1 , wherein the dual channel FMCW signal generator is a digital circuit block.

9. The FMCW radar system of claim 1 , wherein the controller is configured to:

select initial quadrature calibration variables (θ t , A t );

apply the initial quadrature calibration variables (θ t , A t ) as input to the dual output FMCW signal generator;

receive an in-phase beat signal from a first output of the dual channel ADC and a quadrature beat signal from a second output of the dual channel ADC based on the applied initial quadrature calibration variables (θ t , A t );

correlate the in-phase beat signal with the quadrature beat signal; and

upon determining that the correlation is below a predetermined threshold, select new quadrature calibration variables (θ t , A t ).

10. A method of automatic image rejection of a frequency modulated continuous-wave (FMCW) radar system, comprising:

generating a quadrature FMCW signal comprising an in-phase signal and a quadrature signal by a dual output FMCW signal generator;

transmitting the in-phase signal and the quadrature signal by way of a transmitter of a transceiver;

receiving a radar signal comprising a response in-phase signal and a response quadrature signal in response to the transmitted in-phase signal and the quadrature signal of the transceiver;

providing the response in-phase signal and the response quadrature signal to a dual channel analog to digital converter (ADC);

receiving, by a controller, a windowing signal that indicates a start and an end of a frequency ramp cycle of the generated quadrature FMCW signal;

extracting, by the controller, an in-phase beat signal (Beat-I) and a quadrature beat signal (Beat-Q) from the dual channel ADC, based on the received windowing signal;

correlating, by the controller, between the Beat-I and the Beat-Q; and

generating, by the controller, a relative phase and/or amplitude adjustment by providing a phase calibration variable (θ t ) and/or an amplitude calibration variable (A t ) as input to the dual output FMCW signal generator, based on the correlation.

11. The method of claim 10 , further comprising upon determining that a threshold correlation is not achieved, iteratively adjusting the phase calibration variable (θ t ) and/or the amplitude calibration variable (A t ) as input to the dual output FMCW signal generator, until the threshold correlation is achieved.

12. The method of claim 10 , further comprising:

splitting the in-phase signal of the FMCW signal by a first power splitter into a first in-phase signal of the FMCW signal that is provided to the transmitter and a second in-phase signal of the FMCW signal as a first in-phase input to a first mixer; and

splitting the quadrature signal of the FMCW signal by a second power splitter into a first quadrature signal of the FMCW signal that is provided to the transmitter and a second quadrature signal of the FMCW signal as a first quadrature input to a second mixer.

13. The method of claim 12 , further comprising:

mixing, by the first mixer, the first in-phase input with an in-phase radar signal received by the receiver and providing a result as a first input to the dual channel analog to digital converter (ADC); and

mixing, by the second mixer, the first quadrature input with a quadrature radar signal received by the receiver and providing a result as a second input to the dual channel ADC.

14. The method of claim 10 , further comprising adjusting at least one of a direction of the transmitter or the receiver to increase a signal reflection to enhance a calibration capability of the FMCW radar system.

15. A method of calibrating a frequency modulated continuous-wave (FMCW) radar system comprising:

providing a quadrature transceiver comprising a transmitter having an in-phase input and a quadrature input, and a receiver having an in-phase output and a quadrature output;

providing a dual channel FMCW signal generator having two direct digital synthesizers (DDSs) and comprising a first output coupled to the in-phase input of the transmitter, and a second output coupled to the quadrature input of the transmitter;

coupling a first splitter between the first output of the dual channel FMCW signal generator and the in-phase input of the transmitter;

coupling a second splitter between the second output of the dual channel FMCW signal generator and the quadrature input of the transmitter;

providing a first mixer comprising a first input coupled to a second output of the first splitter, a second input coupled to the in-phase output of the receiver, and an output of the first mixer;

providing a second mixer comprising a first input coupled to a second output of the second splitter, a second input coupled to the quadrature output of the receiver and an output of the second mixer;

providing a dual channel analog to digital converter (ADC) comprising a first input coupled to the output of the first mixer, and a second input coupled to the output of the second mixer; and

coupling a controller between the dual channel FMCW signal generator and the dual channel ADC.

16. The method of claim 15 , further comprising:

receiving, by the dual channel FMCW signal generator, a phase calibration variable (θ t ) and/or an amplitude calibration variable (A t ); and

programming the dual channel FMCW signal generator based on the received phase calibration variable (θ t ) and/or the amplitude calibration variable (A t ).

17. The method of claim 15 , further comprising providing a windowing signal, by the dual channel FMCW signal generator, which indicates a start and an end of each frequency ramp cycle of the dual channel FMCW signal generator.

18. The method of claim 15 , further comprising receiving, by a quadrature calibration block of the controller, an in-phase beat signal from a first output of the dual channel ADC and a quadrature beat signal from a second output of the dual channel ADC.

19. The method of claim 18 , further comprising providing at least one of a phase calibration variable (θ t ) or an amplitude calibration variable (A t ) as input to the dual output FMCW signal generator, by the quadrature calibration block of the controller.

20. The method of claim 15 , further comprising:

selecting, by the controller, initial quadrature calibration variables (θ t , A t );

applying, by the controller, the initial quadrature calibration variables (θ t , A t ) as input to the dual output FMCW signal generator;

receiving, by the controller, an in-phase beat signal from a first output of the dual channel ADC and a quadrature beat signal from a second output of the dual channel ADC based on the applied initial quadrature calibration variables (θ t , A t );

correlating, by the controller, the in-phase beat signal with the quadrature beat signal; and

upon determining that the correlation is below a predetermined threshold, selecting, by the controller, new quadrature calibration variables (θ t , A t ) to be applied to the dual output FMCW signal generator.