Methods and systems for calibrating a frequency-division duplexing transceiver

1. A frequency-division duplexing transceiver, comprising:

a first mixer to up-convert a transmit signal;

a first switch, coupled to the first mixer, to selectively provide a transmit local oscillator signal or a receive local oscillator signal to the first mixer, wherein the transmit local oscillator signal has a first frequency and the receive local oscillator signal has a second frequency distinct from the first frequency, and wherein the first switch is to provide the transmit local oscillator signal to the first mixer during a normal mode and a transmitter calibration mode;

a second mixer to down-convert a receive signal; and

a second switch, coupled to the second mixer, to selectively provide the transmit local oscillator signal or the receive local oscillator signal to the second mixer, wherein the second switch is to provide the transmit local oscillator signal to the second mixer during the transmitter calibration mode.

2. The transceiver of claim 1 , further comprising a loop-back path to selectively couple an output of the first mixer to an input of the second mixer.

3. The transceiver of claim 2 , wherein the loop-back path comprises a phase shifter.

4. The transceiver of claim 3 , wherein the phase shifter comprises a phase shift element and a switch to selectively bypass the phase shift element.

5. The transceiver of claim 3 , wherein the loop-back path further comprises a switch, in series with the phase shifter, to selectively open or close the loop-back path.

6. The transceiver of claim 1 , wherein:

the first switch is to provide the receive local oscillator signal to the first mixer during a receiver calibration mode; and

the second switch is to provide the receive local oscillator signal to the second mixer during the normal mode and the receiver calibration mode.

7. The transceiver of claim 1 , wherein the transmit signal is an in-phase transmit signal, the transmit local oscillator signal is an in-phase transmit local oscillator signal, and the receive local oscillator signal is an in-phase receive local oscillator signal, the transceiver further comprising:

a third mixer to up-convert a quadrature transmit signal;

a third switch, coupled to the third mixer, to selectively provide a quadrature transmit local oscillator signal or a quadrature receive local oscillator signal to the third mixer, wherein the quadrature transmit local oscillator signal has the first frequency and the quadrature receive local oscillator signal has the second frequency;

a fourth mixer to down-convert the receive signal; and

a fourth switch, coupled to the fourth mixer, to selectively provide the quadrature transmit local oscillator signal or the quadrature receive local oscillator signal to the second mixer.

8. The transceiver of claim 7 , wherein:

the third switch is to provide the quadrature transmit local oscillator signal to the third mixer during the normal mode and the transmitter calibration mode; and

the fourth switch is to provide the quadrature transmit local oscillator signal to the fourth mixer during the transmitter calibration mode.

9. The transceiver of claim 8 , wherein:

the first switch is to provide the in-phase receive local oscillator signal to the first mixer during a receiver calibration mode;

the third switch is to provide the quadrature receive local oscillator signal to the third mixer during the receiver calibration mode;

the second switch is to provide the in-phase receive local oscillator signal to the second mixer during the normal mode and the receiver calibration mode; and

the fourth switch is to provide the quadrature receive local oscillator signal to the fourth mixer during the normal mode and the receiver calibration mode.

10. The transceiver of claim 7 , further comprising:

a combiner to combine the up-converted in-phase and quadrature transmit signals; and

a loop-back path to selectively couple an output of the combiner to an input of the second and fourth mixers.

11. The transceiver of claim 10 , further comprising:

a first amplifier coupled between the combiner and the loop-back path; and

a second amplifier coupled between the loop-back path and the input of the second and fourth mixers.

12. A method of operating a frequency-division duplexing transceiver, comprising:

in a normal mode:

providing a transmit local oscillator signal to a first mixer to up-convert a transmit signal, wherein the transmit local oscillator signal has a first frequency, and

providing a receive local oscillator signal to a second mixer to downconvert a receive signal, wherein the receive local oscillator signal has a second frequency distinct from the first frequency; and

in a transmitter calibration mode, providing transmit local oscillator signal to the first and second mixers.

13. The method of claim 12 , further comprising, in the transmitter calibration mode, configuring a loop-back path to couple an output of the first mixer to an input of the second mixer.

14. The method of claim 13 , further comprising, in the transmitter calibration mode:

transmitting a signal through the loop-back path; and

phase-shifting the signal in the loop-back path.

15. The method of claim 13 , further comprising, in the transmitter calibration mode:

switching a phase-shift element out of the loop-back path;

with the phase-shift element switched out of the loop-back path, transmitting a first signal through the loop-back path;

switching the phase-shift element into the loop-back path; and

with the phase-shift element switched into the loop-back path, transmitting a second signal through the loop-back path.

16. The method of claim 13 , further comprising, in the normal mode, opening the loop-back path to de-couple the output of the first mixer from the input of the second mixer.

17. The method of claim 12 , further comprising

providing the receive local oscillator signal to the first and second mixers in a receiver calibration mode.

18. The method of claim 12 , wherein the transmit signal is an in-phase transmit signal, the transmit local oscillator signal is an in-phase transmit local oscillator signal, and the receive local oscillator signal is an in-phase receive local oscillator signal, the method further comprising:

in the normal mode:

providing a quadrature transmit local oscillator signal to a third mixer to up-convert a quadrature transmit signal, and

providing a quadrature receive local oscillator signal to a fourth mixer to down-convert the receive signal, wherein the quadrature transmit local oscillator signal has the first frequency and the quadrature receive local oscillator signal has the second frequency; and

in the transmitter calibration mode, providing the quadrature transmit local oscillator signal to the third and fourth mixers.

19. The method of claim 18 , further comprising, in a receiver calibration mode:

providing the in-phase receive local oscillator signal to the first and second mixers; and

providing the quadrature receive local oscillator signal to the third and fourth mixers.

20. The method of claim 18 , further comprising, in the transmitter calibration mode:

combining outputs of the first and third mixers to generate a first signal and a second signal;

configuring a loop-back path to provide the first and second signals to inputs of the second and fourth mixers;

switching a phase-shifter out of the loop-back path;

with the phase-shifter switched out of the loop-back path, transmitting the first signal through the loop-back path to the second and fourth mixers;

switching the phase-shifter into the loop-back path; and

with the phase-shifter switched into the loop-back path, transmitting the second signal through the loop-back path to the second and fourth mixers.

21. A non-transitory computer-readable storage medium storing instructions, which when executed by a processor in a communication device comprising a transceiver, cause the transceiver to:

provide a transmit local oscillator signal to a first mixer to up-convert a transmit signal in a normal mode, wherein the transmit local oscillator signal has a first frequency;

provide a receive local oscillator signal to a second mixer to down-convert a receive signal in the normal mode, wherein the receive local oscillator signal has a second frequency distinct from the first frequency; and

provide the transmit local oscillator signal to the first and second mixers in a transmitter calibration mode.

22. A frequency-division duplexing transceiver, comprising:

a first mixer to up-convert a transmit signal;

a second mixer to down-convert a receive signal;

means for selectively providing a transmit local oscillator signal or a receive local oscillator signal to the first mixer, wherein the transmit local oscillator signal has a first frequency and the receive local oscillator signal has a second frequency distinct from the first frequency, and wherein the transmit local oscillator signal is to be provided to the first mixer during a normal mode and a transmitter calibration mode; and

means for selectively providing the transmit local oscillator signal or the receive local oscillator signal to the second mixer, wherein the transmit local oscillator signal is to be provided to the second mixer during the transmitter calibration mode.

23. The non-transitory computer-readable storage medium of claim 21 , wherein the instructions, when executed by the processor, further cause the transceiver to provide the receive local oscillator signal to the first and second mixers in a receiver calibration mode.