Antenna tuning using the ratio of complex forward and reflected signals

1. A method for controlling an antenna tuner coupled between a power amplifier (PA) and an antenna in a wireless device, comprising:

measuring forward and reflected signal components at an output of the PA, wherein the forward and reflected signal components result from applying an input signal to a transmit path of the wireless device;

generating amplitude and phase information from each of the measured forward and reflected signal components, wherein generating the amplitude and phase information from each of the measured forward and reflected signal components comprises down-converting and digitizing the forward and reflected signal components to generate respectively forward digital baseband in-phase (I) and quadrature (Q) signals and reflected digital baseband I and Q signals;

estimating a voltage reflection coefficient using the generated amplitude and phase information; and

adjusting the antenna tuner based on the voltage reflection coefficient to reduce an impedance mismatch between the PA and the antenna.

2. The method of claim I, wherein measuring the forward and reflected signal components comprises selectively controlling directional coupler coupled to the output of the PA.

3. The method of claim 1 , wherein the down-converting and digitizing of the forward and reflected signal components are performed by a feedback path of the wireless device, the method further comprising:

compensating the generated forward and reflected digital baseband I and Q signals to eliminate a gain mismatch introduced by the feedback path.

4. The method of claim 1 , wherein estimating the voltage reflection coefficient using the generated amplitude and phase information comprises:

estimating a forward complex gain and a reverse complex gain of the transmit path using the input signal and the generated amplitude and phase information; and

estimating the voltage reflection coefficient as a ratio of the reverse complex gain to the forward complex gain of the transmit path.

5. The method of claim 4 , wherein the input signal comprises input digital baseband I and Q signals, wherein estimating the forward or reverse complex gain of the transmit path comprises:

generating a DC offset-compensated cross-correlation product between the forward or reflected digital baseband I and Q signals and the input digital baseband I and Q signals;

generating a DC offset-compensated auto-correlation product of the input I and Q digital baseband signals; and

generating the forward or reverse complex gain as a ratio of the DC offset-compensated cross-correlation product to the DC offset-compensated auto-correlation product.

6. The method of claim 1 , wherein the antenna tuner includes a pi network having one or more variable capacitors.

7. The method of claim 1 . wherein the voltage reflection coefficient is an input reflection coefficient.

8. The method of claim 1 , wherein the transmit path begins at an output of a digital module that produces the input signal and ends at the output of the PA.

9. The method of claim 1 . wherein adjusting the antenna tuner includes adjusting the antenna tuner to match an impedance presented by the antenna to the PA to a target impedance value.

10. A wireless device, comprising:

a digital nodule configured to generate an input signal;

a transmit path, comprising:

a filtering and up-conversion module configured to generate a radio frequency (RF) signal from the input signal; and

a power amplifier (PA) configured to power amplify the RF signal to generate an output waveform;

an antenna configured to receive and transmit the output waveform;

an antenna tuner coupled between the PA and the antenna; and

a feedback path, comprising:

a directional coupler configured to receive forward and reflected signal components at an output of the PA, wherein the forward and reflected signal components result from applying the input signal to the transmit path; and

a RF receiver configured to generate amplitude and phase information from each of the forward and reflected signal components and further configured to down-convert and digitize the forward and reflected signal components to generate respectively forward digital baseband in-phase (I) and quadrature (Q) signals and reflected digital baseband I and Q signals;

wherein the digital module is further configured to estimate a voltage reflection coefficient using the generated amplitude and phase information, and to adjust the antenna tuner based on the voltage reflection coefficient to reduce an impedance mismatch between the PA and the antenna.

11. The wireless device of claim 10 , wherein the feedback path further comprises:

a compensator module configured to compensate the generated forward and reflected digital baseband I and Q signals to eliminate a gain mismatch introduced by the feedback path.

12. The wireless device of claim 10 , Wherein the digital module is further configured to estimate a forward complex gain and a reverse complex gain of the transmit path using the input signal and the generated amplitude and phase information.

13. The wireless device of claim 12 , wherein the digital module is further configured to estimate the voltage reflection coefficient as a ratio of the reverse complex gain to the forward complex gain of the transmit path.

14. The wireless device of claim 12 , wherein the input signal comprises input digital baseband I and Q signals, the wireless device further comprising:

a TX statistics calculator module configured to generate a DC offset-compensated cross-correlation product between the forward or reflected digital baseband I and Q signals and the input digital baseband I and Q signals, and to generate a DC offset-compensated auto-correlation product of the input I and Q digital baseband signals.

15. The wireless device of claim 14 , wherein the digital module is further configured to generate the forward or reverse complex gain as a ratio of the DC offset compensated cross-correlation product to the DC offset-compensated auto-correlation product.

16. The wireless device of claim 10 , wherein the digital module is configured to adjust the antenna tuner based on the voltage reflection coefficient to match an impedance presented by the antenna to the PA to a target impedance value.

17. The wireless device of claim 10 , wherein the antenna tuner includes a pi network having one or more variable capacitors.

18. The wireless device of claim 10 , wherein the voltage refection coefficient is an input reflection coefficient.

19. A method for controlling an antenna tuner coupled between a power amplifier (PA) and an antenna in a wireless device, comprising:

measuring forward and reflected signal components at an output of the PA to produce measurements, wherein the measurements are responsive to a phase of said forward and reflected signal components;

estimating forward complex gain and a reverse complex gain using the measurements;

estimating voltage reflection coefficient as a ratio of the reverse complex to the forward complex gain; and

adjusting the antenna timer based on the voltage reflection coefficient.

20. The method of claim 19 , wherein the measuring of the forward and reflected signal components is performed using a directional coupler.

21. The method of claim 19 , wherein the measurements are further responsive to an amplitude of said forward and reflected signal components.

22. The method of claim 19 , wherein the forward and reflected signal components result from applying an input signal to a transmit path of the wireless device, and wherein estimating the forward complex gain and the reverse complex gain comprises:

generating a complex forward signal and a complex reflected signal from the forward signal components and the reflected signal components respectively;

generating first and second cross-correlation products between the complex forward signal and the input signal and between the complex reflected signal and the input signal respectively;

generating an auto-correlation product of the input signal:

generating the forward complex gain as a ratio of the first cross-correlation product to the auto-correlation product of the input signal; and

generating the reverse complex gain as a ratio of the second cross-correlation product to the auto-correlation product of the input signal.

23. The method of claim 19 , wherein generating the complex forward signal and the complex reflected signal comprises down-converting and digitizing the forward and reflected signal components.