Methods and Apparatus for Reducing Own-Transmitter Interference in Low-IF and Zero-IF Receivers

• US 20090325509A1
• Filed: 06/27/2008
• Published: 12/31/2009
• Est. Priority Date: 06/27/2008
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Mattisson, Sven, Dent, Paul Wilkinson
• Granted Patent: US 8,855,580 B2
• Time in Patent Office: Days
• US Class Current: 455/75
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver

Abstract

Circuits and methods are disclosed for reducing interference from transmitter leakage in a radio transceiver. An exemplary method for reducing interference from transmitter leakage in a radio transceiver comprises downconverting, filtering, and sampling a radio frequency signal comprising a desired signal and a transmitter leakage signal to obtain a sampled signal of interest. The method further comprises generating a sampled distortion signal estimate that estimates one or more distortion products of the transmitter leakage signal, such as a squared amplitude obtained from a square-law device or corresponding digital function. Finally, the method comprises combining the sampled distortion signal estimate with the sampled signal of interest to obtain interference-reduced signal samples. In some embodiments, this may comprise correlating the sampled distortion signal estimate with the sampled signal of interest to determine a scaling factor, scaling the sampled distortion signal estimate with the scaling factor, and subtracting the scaled distortion signal estimate from the sampled signal of interest to obtain the interference-reduced signal samples.

Claims

1. A radio transceiver circuit, comprising:

a receiver circuit configured to downconvert, filter, and sample a radio frequency signal comprising a desired signal and a transmitter leakage signal to obtain a sampled signal of interest;

a distortion estimation circuit configured to generate a sampled distortion signal estimate of one or more distortion products of the transmitter leakage signal; and

an interference subtraction circuit configured to combine the sampled distortion signal estimate with the sampled signal of interest to obtain interference-reduced signal samples.

2. The radio transceiver circuit of claim 1, wherein the receiver circuit comprises a homodyne downconverter for downconverting the radio frequency signal.

3. The radio transceiver circuit of claim 1, wherein the transmitter leakage signal has a modulation bandwidth, and wherein the receiver circuit is configured to downconvert the radio frequency signal to an intermediate frequency less than the modulation bandwidth of the transmitter leakage signal.

4. The radio transceiver circuit of claim 1, wherein the distortion estimation circuit comprises one or more analog non-linear components configured to produce estimates of non-linear products of the transmitter leakage from a transmitter signal and an analog-to-digital converter to produce the sampled distortion signal estimate from the non-linear products.

5. The radio transceiver circuit of claim 4, wherein the one or more analog non-linear components include a square-law device for generating a second-order distortion product of the transmitter signal.

6. The radio transceiver circuit of claim 4, wherein the distortion estimation circuit further comprises one or more analog filters matched to one or more receive filters in the receiver circuit.

7. The radio transceiver circuit of claim 1, wherein the distortion estimation circuit comprises digital distortion processing circuitry configured to generate the sampled distortion signal estimate.

8. The radio transceiver circuit of claim 7, wherein the digital distortion processing circuitry is configured to generate the sampled distortion signal estimate from a digital transmitter modulation signal.

9. The radio transceiver circuit of claim 7, wherein the distortion estimation circuit further comprises one or more digital filters configured to match the response of one or more filters in the receiver circuit.

10. The radio transceiver circuit of claim 1, wherein the interference subtraction circuit comprises:

a correlator circuit configured to correlate the sampled signal of interest with the sampled distortion signal estimate to obtain a scaling factor;

a scaling circuit configured to scale the sampled distortion signal estimate, using the scaling factor; and

a subtracting circuit configured to subtract the scaled sampled distortion signal estimate from the sampled signal of interest to obtain the interference-reduced signal samples.

11. The radio transceiver circuit of claim 10, wherein the correlator circuit is configured to perform two or more correlations between the sampled signal of interest and the sampled distortion signal estimate, using varying relative delays, and to select the scaling factor corresponding to the highest correlation for use in scaling the sampled distortion signal estimate.

12. The radio transceiver circuit of claim 1, wherein the interference subtraction circuit comprises:

a correlator circuit configured to perform two or more correlations between the sampled signal interest and the sampled distortion signal estimate, using varying relative delays, to obtain scaling factors corresponding to the relative delays; and

a subtracting circuit configured to subtract two or more scaled versions of the sampled distortion signal estimate, each with a different relative delay, from the sampled signal of interest to obtain the interference-reduced signal samples.

13. The radio transceiver circuit of claim 1, further comprising a phase-rotating circuit configured to phase-rotate the interference-reduced signal samples to obtain baseband signal samples.

14. A method for reducing interference from transmitter leakage in a radio transceiver, the method comprising:

downconverting, filtering, and sampling a radio frequency signal comprising a desired signal and a transmitter leakage signal to obtain a sampled signal of interest;

generating a sampled distortion signal estimate of one or more distortion products of the transmitter leakage signal; and

combining the sampled distortion signal estimate with the sampled signal of interest to obtain interference-reduced signal samples.

15. The method of claim 14, wherein downconverting, filtering, and sampling the radio frequency signal comprises downconverting the radio frequency signal to baseband using a homodyne downconverter.

16. The method of claim 14, wherein downconverting, filtering, and sampling the radio frequency signal comprises downconverting the radio frequency signal to an intermediate frequency less than a modulation bandwidth of the transmitter leakage signal.

17. The method of claim 14, wherein generating the sampled distortion signal estimate comprises producing estimates of non-linear products of the transmitter leakage from a transmitter signal, using one or more analog non-linear components, and sampling the non-linear products to produce the sampled distortion signal estimate.

18. The method of claim 17, wherein producing estimates of non-linear products of the transmitter leakage comprises generating a second-order distortion product of the transmitter signal using a square-law device.

19. The method of claim 14, wherein generating the sampled distortion signal estimate comprises generating the sampled distortion signal estimate from a digital transmitter modulation signal.

20. The method of claim 19, further comprising digitally filtering the sampled distortion signal estimate using one or more digital filters configured to match the response of one or more filters in the receiver circuit.

21. The method of claim 14, wherein combining the sampled distortion signal estimate with the sampled signal of interest comprises:

correlating the sampled signal of interest with the sampled distortion signal estimate to obtain a scaling factor;

scaling the sampled distortion signal estimate, using the scaling factor; and

subtracting the scaled sampled distortion signal estimate from the sampled signal of interest to obtain the interference-reduced signal samples.

22. The method of claim 21, wherein correlating the sampled signal of interest with the sampled distortion signal estimate comprises performing two or more correlations between the sampled signal of interest and the sampled distortion signal estimate, using varying relative delays, and selecting the scaling factor corresponding to the highest correlation for use in scaling the sampled distortion signal estimate.

23. The method of claim 14, wherein combining the sampled distortion signal estimate with the sampled signal of interest comprises:

performing two or more correlations between the sampled signal interest and the sampled distortion signal estimate, using varying relative delays, to obtain scaling factors corresponding to the relative delays; and

subtracting two or more scaled versions of the sampled distortion signal estimate, each with a different relative delay, from the sampled signal of interest to obtain the interference-reduced signal samples.