DISTORTION COMPENSATION IN A COMMUNICATION SYSTEM

• US 20090116578A1
• Filed: 11/07/2007
• Published: 05/07/2009
• Est. Priority Date: 11/07/2007
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Copeland, Gregory C., Sperlich, Roland
• Granted Patent: US 7,778,345 B2
• Time in Patent Office: Days
• US Class Current: 375/285
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H04B 2001/0425 with linearisation using predistortion

Abstract

In one embodiment of the invention, a modulator mixes a transmit-path signal based on a local oscillator (LO) signal and an amplifier amplifies the mixed transmit-path signal to generate an output signal for transmission. A demodulator generates a receive-path signal based on the output signal and the LO signal. Phase-shift control components provide the output signal and the LO signal to the demodulator during a first time duration and provide a phase-shifted version of one of the output signal and the LO signal to the demodulator during a second time duration. The demodulator generates a second receive-path signal based on the one of the phase-shifted output signal and the phase-shifted LO signal during the second time duration. At least one predistortion circuit adjusts at least one of the transmit-path signal and the receive-path signal based on a difference in signal characteristics of the receive-path signal during the second time duration relative to the first time duration.

Claims

1. A communication system comprising:

a modulator configured to mix a transmit-path signal based on a local oscillator (LO) signal;

an amplifier configured to amplify the mixed transmit-path signal to generate an output signal for transmission;

a demodulator configured to generate a receive-path signal based on the output signal and the LO signal;

phase-shift control components configured to provide the output signal and the LO signal to the demodulator during a first time duration and to provide a phase-shifted version of one of the output signal and the LO signal to the demodulator during a second time duration, the demodulator being configured to generate a second receive-path signal based on the one of the phase-shifted output signal and the phase-shifted LO signal during the second time duration; and

at least one predistortion circuit configured to adjust at least one of the transmit-path signal and the receive-path signal based on a difference in signal characteristics of the receive-path signal during the second time duration relative to the first time duration.

2. The communication system of claim 1, wherein each of the transmit-path signal and the receive-path signal comprise an in-phase component and a quadrature-phase component.

3. The communication system of claim 2, wherein the at least one predistortion circuit is configured to correct an imbalance between the in-phase component and the quadrature-phase component of the at least one of the transmit-path signal and the receive-path signal.

4. The communication system of claim 2, wherein the at least one predistortion circuit is configured to adjust at least one of gain and DC-offset associated with each of the in-phase component and the quadrature-phase component of the at least one of the transmit-path signal and the receive-path signal.

5. The communication system of claim 1, wherein the phase control circuitry comprises a phase-shifter configured to generate the one of the phase-shifted output signal and the phase-shifted LO signal, the demodulator being coupled to the phase-shifter during the second time duration.

6. The communication system of claim 1, further comprising a first local oscillator configured to generate the LO signal and wherein the phase control circuitry comprises a second local oscillator configured to generate the one of the phase-shifted output signal and the phase-shifted LO signal, the demodulator being coupled to the second local oscillator during the second time duration.

7. The communication system of claim 1, wherein the phase control circuitry comprises a microcontroller configured to generate a low-frequency signal that is mixed with one of the LO signal and the output signal to generate the one of the phase-shifted output signal and the phase-shifted LO signal during the second time duration.

8. The communication system of claim 1, further comprising a digital signal processor (DSP) configured to monitor the signal characteristics of the receive-path signal during the first time duration and the second time duration and to calculate at least one compensation component that is provided to the at least one predistortion circuit.

9. The communication system of claim 8, wherein the at least one compensation component comprises a DC-offset and at least one gain associated with each of an in-phase component and a quadrature-phase component associated with the respective at least one of the transmit-path signal and the receive-path signal.

10. The communication system of claim 8, wherein the DSP is configured to periodically monitor the signal characteristics and to periodically calculate the compensation components.

11. The communication system of claim 1, wherein the at least one predistortion circuit comprises a transmit-path predistortion circuit and a receive-path predistortion circuit.

12. A method for correcting in-phase and quadrature-phase imbalance associated with at least one of a transmit-path signal and a receive-path signal, the method comprising:

mixing the transmit-path signal with a local oscillator (LO) signal to generate a radio frequency (RF) signal;

amplifying the RF signal to generate an output signal for transmission;

reverse-mixing the output signal to generate a first receive-path signal based on the LO signal;

monitoring signal characteristics associated with the first receive-path signal;

reverse-mixing one of the output signal based on a phase-shifted version of the LO signal and a phase-shifted version of the output signal based on the LO signal to generate a second receive-path signal;

monitoring signal characteristics associated with the second receive-path signal; and

adjusting at least one of the transmit-path signal and the receive-path signal based on a difference in the monitored signal characteristics of the first receive-path signal and the monitored signal characteristics of the second receive-path signal.

13. The method of claim 12, wherein adjusting the at least one of the transmit-path signal and the receive-path signal comprises adjusting at least one of a DC-offset and at least one gain associated with each of an in-phase component and a quadrature-phase component of the at least one of the transmit-path signal and the receive-path signal.

14. The method of claim 12, further comprising:

generating the LO signal from a first local oscillator; and

generating the phase-shifted version of the LO signal from a second local oscillator;

wherein the reverse-mixing comprises switching between the first local oscillator to generate the first receive-path signal during a first time duration and the second local oscillator to generate the second receive-path signal during a second time duration.

15. The method of claim 12, further comprising:

generating the LO signal from a first local oscillator; and

mixing the output signal with a second LO signal generated from a second local oscillator to generate the phase-shifted version of the output signal;

wherein the reverse-mixing comprises reverse-mixing the output signal based on the LO signal to generate the first receive-path signal during a first time duration and reverse-mixing the phase-shifted version of the output signal based on the LO signal to generate the second receive-path signal during a second time duration.

16. The method of claim 12, further comprising mixing one of the LO signal and the output signal with a low-frequency signal to generate the respective one of the phase-shifted version of the LO signal and the phase-shifted version of the output signal.

17. A communication system comprising:

means for mixing a transmit-path signal with a local oscillator (LO) signal to generate a radio frequency (RF) signal;

means for amplifying the RF signal to generate an output signal;

means for reverse-mixing the output signal based on the LO signal during a first time duration and for reverse-mixing one of the output signal based on a phase-shifted version of the LO signal and a phase-shifted version of the output signal based on the LO signal to generate the receive-path signal during a second time duration;

means for monitoring signal characteristics associated with the receive-path signal during the first time duration and the second time duration; and

means for adjusting at least one of the transmit-path signal and the receive-path signal based on a difference in the signal characteristics of the receive-path signal during the second time duration relative to the first time duration.

18. The communication system of claim 17, further comprising:

means for phase-shifting one of the LO signal and the output signal; and

means for switching between one of the LO signal and the output signal during the first time duration and one of the phase-shifted version of the LO signal and the phase-shifted version of the output signal during the second time duration.

19. The communication system of claim 17, further comprising:

means for generating a low-frequency signal; and

means for mixing the low-frequency signal with one of the LO signal and the output signal during the second time duration.

20. The communication system of claim 17, further comprising:

means for generating the LO signal; and

means for generating a second LO signal, which is separate from the means for generating the LO signal, the second LO signal being configured to generate one of the phase-shifted version of the LO signal and the phase-shifted version of the output signal.