REDUCTION OF SECOND-ORDER DISTORTION CAUSED BY TRANSMIT SIGNAL LEAKAGE

• US 20080233894A1
• Filed: 03/23/2007
• Published: 09/25/2008
• Est. Priority Date: 03/23/2007
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Aparin, Vladimir
• Granted Patent: US 8,706,055 B2
• Time in Patent Office: Days
• US Class Current: 455/78
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver

Abstract

This disclosure describes techniques for reducing adverse effects of TX signal leakage in a full-duplex, wireless communication system. In particular, the disclosure describes techniques for reducing adverse effects of second order distortion of TX signal leakage. To reduce or eliminate second order distortion of transmit signal leakage, a wireless device squares a combined signal that carries both a desired RX signal and a TX leakage signal. For example, the device may include a device that exhibits a strong, second order nonlinearity to, in effect, square the combined signal. The device subtracts the squared signal from the output of the mixer in the receive path, canceling out at least some of the second-order distortion caused by the mixer. In this manner, the device can reduce the adverse effects of second order distortion of TX signal leakage, and thereby enhance or maintain receiver sensitivity.

Claims

1. A wireless receiver comprising:

a mixer that down-converts an input signal to create a down-converted input signal;

a squaring unit that squares the input signal to create a squared input signal; and

a subtracting unit that subtracts the squared input signal from the down-converted input signal.

2. The receiver of claim 1, wherein the mixer is a first mixer, and wherein the squaring unit comprises a second mixer with a radio frequency (RF) port and a local oscillator (LO) port coupled to one another.

3. The receiver of claim 1, further comprising:

an antenna;

a duplexer coupled to the antenna; and

a low noise amplifier having an input coupled to the duplexer and an output coupled to apply the input signal to the mixer,

wherein the duplexer passes a transmit leakage signal to the low noise amplifier.

4. The receiver of claim 3, further comprising a filter coupled between the low noise amplifier and the mixer.

5. The receiver of claim 4, wherein the filter comprises a radio frequency (RF) surface acoustic wave (SAW) filter.

6. The receiver of claim 1, further comprising:

a first analog-to-digital converter (ADC) that digitizes the down-converted input signal; and

a second ADC that digitizes the squared input signal.

7. The receiver of claim 6, wherein the subtracting unit comprises a digital signal processor (DSP) that subtracts the digitized squared input signal from the digitized, down-converted input signal.

8. The receiver of claim 1, further comprising:

a first analog-to-digital converter (ADC) that digitizes the down-converted input signal;

a baseband filter that filters the squared input signal to create a filtered squared input signal; and

a second ADC that digitizes the filtered squared input signal.

9. The receiver of claim 8, wherein the subtracting unit comprises a digital signal processor (DSP) that subtracts the digitized, filtered, squared input signal from the digitized, down-converted input signal.

10. A method comprising:

down-converting an input signal to create a down-converted input signal;

squaring the input signal to create a squared input signal; and

subtracting the squared input signal from the down-converted input signal.

11. The method of claim 10, wherein squaring the input signal comprises squaring the input signal with a squaring unit, and wherein the squaring unit comprises a mixer with a radio frequency (RF) port and a local oscillator (LO) port coupled to one another.

12. The method of claim 10, wherein down-converting the input signal comprises down-converting the input signal via a mixer, the method further comprising receiving the input signal via an antenna, a duplexer coupled to the antenna, and a low noise amplifier having an input coupled to the duplexer and an output coupled to apply the input signal to the mixer, wherein the duplexer passes a transmit leakage signal to the low noise amplifier.

13. The method of claim 12, further comprising filtering the input signal with a filter coupled between the low noise amplifier and the mixer.

14. The method of claim 13, wherein the filter comprises a radio frequency (RF) surface acoustic wave (SAW) filter.

15. The method of claim 10, further comprising:

digitizing the down-converted input signal; and

digitizing the squared input signal,

wherein subtracting the squared input signal from the down-converted input signal comprises subtracting the digitized squared input signal from the digitized, down-converted input signal.

16. The method of claim 15, further comprising filtering the squared input signal to create a filtered squared input signal, wherein digitizing the squared input signal comprises digitizing the filtered squared input signal.

17. A device comprising:

means for down-converting an input signal to create a down-converted input signal;

means for squaring the input signal to create a squared input signal; and

means for subtracting the squared input signal from the down-converted input signal.

18. The device of claim 17, wherein the means for squaring comprises a mixer with a radio frequency (RF) port and a local oscillator (LO) port coupled to one another.

19. The device of claim 17, further comprising:

means for digitizing the down-converted input signal; and

means for digitizing the squared input signal,

wherein the means for subtracting the squared input signal from the down-converted input signal comprises means for subtracting the digitized squared input signal from the digitized, down-converted input signal.

20. The device of claim 19, further comprising means for filtering the squared input signal to create a filtered squared input signal, wherein the means for digitizing the squared input signal comprises means for digitizing the filtered squared input signal.

21. A wireless communication device comprising:

a radio frequency (RF) transmitter;

an RF receiver;

an RF antenna; and

a duplexer that couples the transmitter and the receiver to the antenna,

wherein the duplexer passes a transmit leakage signal to the low noise amplifier, and

wherein the RF receiver comprises;

a mixer that down-converts an input signal to create a down-converted input signal;

a squaring unit that squares the input signal to create a squared input signal; and

a subtracting unit that subtracts the squared input signal from the down-converted input signal.

22. The device of claim 21, wherein the transmitter is a code division multiple access (CDMA) transmitter and the receiver is a CDMA receiver.

23. The device of claim 21, wherein the mixer is a first mixer, and wherein the squaring unit comprises a second mixer with a radio frequency (RF) port and a local oscillator (LO) port coupled to one another.

24. The device of claim 21, wherein the RF receiver further comprises:

a low noise amplifier having an input coupled to the duplexer and an output coupled to apply the input signal to the mixer; and

a filter coupled between the low noise amplifier and the mixer.

25. The device of claim 24, wherein the filter comprises a radio frequency (RF) surface acoustic wave (SAW) filter.

26. The device of claim 21, wherein the RF receiver further comprises:

a first analog-to-digital converter (ADC) that digitizes the down-converted input signal; and

a second ADC that digitizes the squared input signal.

27. The device of claim 26, wherein the subtracting unit comprises a digital signal processor (DSP) that subtracts the digitized squared input signal from the digitized, down-converted input signal.

28. The device of claim 21, wherein the receiver further comprises:

a first analog-to-digital converter (ADC) that digitizes the down-converted input signal;

a baseband filter that filters the squared input signal to create a filtered squared input signal; and

a second ADC that digitize the filtered squared input signal.

29. The device of claim 28, wherein the subtracting unit comprises a digital signal processor (DSP) that subtracts the digitized, filtered, squared input signal from the digitized, down-converted input signal.

30. A wireless receiver comprising:

an antenna;

a duplexer coupled to the antenna;

a low noise amplifier coupled to amplify an input signal received via the duplexer and the antenna, wherein the duplexer passes a transmit leakage signal to the low noise amplifier;

a filter that filters the amplified input signal;

a mixer that down-converts the filtered, amplified input signal to create a down-converted input signal;

a squaring unit that squares the filtered, amplified input signal to create a squared input signal; and

a subtracting unit that subtracts the squared input signal from the down-converted input signal.