Systems, methods and devices for joint calibration of transmit and receive IQ mismatch

1. A method of compensating for in-phase (I) and quadrature (Q) mismatch (IQMM) in a transceiver, the method comprising:

sending first and second signals from a transmit path through a loopback path, using a phase shifter to introduce a phase shift in at least one of the first and second signals, to obtain first and second signals received by a receive path;

using the first and second signals received by the receive path to obtain joint estimates of transmit and receive IQMM, at least in part, by estimating the phase shift, wherein using the first and second signals received by the receive path to obtain joint estimates of the transmit and receive IQMM comprises processing the first and second signals received by the receive path as a function of one or more frequency-dependent IQMM parameters; and

compensating for IQMM using the joint estimates of the transmit and receive IQMM.

2. The method of claim 1 , further comprising:

sending a third signal from the transmit path through the loopback path, using the phase shifter to introduce a phase shift in at least two of the first, second, and third signals, to obtain a third signal received by the receive path; and

using the first, second, and third signals received by the receive path to obtain the joint estimates of the transmit and receive IQMM, at least in part, by estimating the phase shift.

3. The method of claim 1 , wherein using the first and second signals received by the receive path to obtain the joint estimates of the transmit and receive IQMM is performed using a system of nonlinear equations.

4. The method of claim 1 , wherein compensating for IQMM using the joint estimates of the transmit and receive IQMM comprises estimating coefficients of an IQMM pre-compensator at the transmit path.

5. The method of claim 1 , wherein compensating for IQMM using the joint estimates of the transmit and receive IQMM comprises estimating coefficients of an IQMM compensator at the receive path.

6. The method of claim 1 , wherein the first signal received by the receive path comprises a component at a principle frequency of the first signal and a component at a mirror frequency of the first signal.

7. The method of claim 1 , wherein the joint estimates of the transmit and receive IQMM are obtained by solving a system of equations, and one or more of the equations comprises:

at least one of the first or second signals received by the receive path;

a first parameter representing, at least in part, the phase shift;

a second parameter representing, at least in part, a desired frequency response of the transmit path;

a third parameter representing, at least in part, a frequency response of the transmit path due to transmit IQMM;

a fourth parameter representing, at least in part, a desired frequency response of the receive path; and

a fifth parameter representing, at least in part, a frequency response of the receive path due to receive IQMM.

8. The method of claim 7 , wherein the one or more of the equations further comprises:

a sixth parameter representing, at least in part, a gain and delay for the transmit path; and

a seventh parameter representing, at least in part, a gain and delay for the receive path.

9. The method of claim 8 , wherein:

the desired frequency response of the transmit path depends, at least in part, on a frequency response of an in-phase filter in the transmit path, a frequency response of a quadrature filter in the transmit path, a phase mismatch between an in-phase mixer and a quadrature mixer in the transmit path, and a gain mismatch between the in-phase mixer and the quadrature mixer in the transmit path; and

the frequency response of the transmit path due to transmit IQMM depends, at least in part, on the frequency response of the in-phase filter in the transmit path, the frequency response of the quadrature filter in the transmit path, the phase mismatch between the in-phase mixer and the quadrature mixer in the transmit path, and the gain mismatch between the in-phase mixer and the quadrature mixer in the transmit path.

10. The method of claim 8 , wherein:

the desired frequency response of the receive path depends, at least in part, on a frequency response of an in-phase filter in the receive path, a frequency response of a quadrature filter in the receive path, a phase mismatch between an in-phase mixer and a quadrature mixer in the receive path, and a gain mismatch between the in-phase mixer and the quadrature mixer in the receive path; and

the frequency response of the receive path due to receive IQMM depends, at least in part, on the frequency response of the in-phase filter in the receive path, the frequency response of the quadrature filter in the receive path, the phase mismatch between the in-phase mixer and the quadrature mixer in the receive path, and the gain mismatch between the in-phase mixer and the quadrature mixer in the receive path.

11. The method of claim 1 , wherein:

the joint estimates of the transmit and receive IQMM are obtained using a first iterative algorithm based on an initial estimate; and

the initial estimate is obtained using a second algorithm.

12. The method of claim 11 , wherein the first iterative algorithm comprises a block coordinate descent, and the second algorithm comprises a matrix inversion.

13. A system comprising:

a quadrature transceiver having a transmit path with a quadrature up-converter, a receive path with a quadrature down-converter, and a loopback path coupled between the up-converter and the down-converter;

a signal generator arranged to apply first and second pilot signals to the transmit path;

a signal observer arranged to capture the first and second pilot signals received from the receive path;

a phase shifter arranged to apply a phase shift to at least one of the first and second pilot signals between the up-converter and the down-converter; and

a processor configured to:

obtain estimated in-phase (I) and quadrature (Q) mismatch (IQMM) parameters for the transmit path and the receive path by estimating the phase shift; and

estimate one or more compensation coefficients for the quadrature transceiver based on the estimated IQMM parameters.

14. The system of claim 13 further comprising an IQMM pre-compensator arranged to compensate an IQMM of the transmit path based on one or more of the compensation coefficients.

15. The system of claim 13 further comprising an IQMM compensator arranged to compensate an IQMM of the receive path based on one or more of the compensation coefficients.

16. A method comprising:

estimating an initial value of a phase mismatch for a receive (RX) path of a quadrature transceiver;

estimating an initial value of a cross multiplication factor for a real-value compensator (RVC) for the RX path based on the initial value of the RX phase mismatch;

obtaining a re-estimate of the RX phase mismatch; and

correcting the initial value of the cross multiplication factor based on the re-estimate of the RX phase mismatch.

17. The method of claim 16 wherein, obtaining the re-estimate of the RX phase mismatch comprises:

obtaining one or more RVC parameters for the RVC;

obtaining an estimated transmit (TX) phase mismatch for a TX path of the quadrature transceiver;

applying the RVC with the one or more RVC parameters to a time-domain signal received without phase shift at baseband of the RX path, thereby generating a compensated time-domain signal; and

re-estimating a residual RX phase mismatch based on the compensated time-domain signal and the estimated TX phase mismatch.

18. The method of claim 17 , wherein, the re-estimate of the RX phase mismatch is a first re-estimate for a first pilot signal at a first frequency, and the method further comprises:

obtaining a second re-estimate of the RX phase mismatch for a second pilot signal at a second frequency; and

correcting the initial value of the cross multiplication factor based on the first and second re-estimate of the RX phase mismatch.

19. The method of claim 18 , further comprising:

obtaining a third re-estimate of the RX phase mismatch for a third pilot signal at a third frequency; and

correcting the initial value of the cross multiplication factor based on the first, second, and third re-estimate of the RX phase mismatch.