Wireless receiver with notch filter to reduce effects of transmit signal leakage

• US 8,036,623 B2
• Filed: 07/12/2007
• Issued: 10/11/2011
• Est. Priority Date: 03/13/2007
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Gudem, Prasad S., Cabanillas, Jose, Chang, Li-Chung
• Primary Examiner(s): LE, THANH C
• Application Number:
  US11/777,249
• Publication Number:
  US 20080227409A1
• Time in Patent Office: 1,552 Days
• Field of Search: 455/296, 455/303, 455/304, 455/305, 455/307, 455/339, 375/349, 375/350, 375/351
• US Class Current: 455/296
• CPC Class Codes: H04B 1/1036 with automatic suppression of narrow band noise or interference, e.g. by using tuneable notch filters H04B1/123 takes precedence; filter circuits H03H
• 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 device. The techniques make use of a notch filter to reject TX signal leakage in a signal processed in the RX path of the wireless communication device. The notch filter may be constructed as a complex notch filter using passive resistor and capacitor components to produce a notch frequency that attenuates TX signal leakage components in a desired signal. The notch filter may be applied to a down-converted, baseband signal produced by a passive mixer.

Claims

1. A radio frequency (RF) receiver comprising:

an amplifier that amplifies a received RF input signal comprising a desired signal and a transmit leakage signal;

a mixer that down-converts a frequency of the amplified signal; and

a notch filter that filters the down-converted signal to substantially reduce the down-converted transmit leakage signal, the notch filter having a notch frequency substantially equal to an offset frequency of the down-converted transmit leakage signal relative to the down-converted desired signal.

2. The receiver of claim 1, wherein the mixer comprises a passive mixer, and the notch filter comprises a complex notch filter comprising an arrangement of resistors and capacitors.

3. The receiver of claim 2, wherein the amplifier and the mixer comprise differential outputs, the mixer generating positive and negative in-phase (I) components and positive and negative quadrature (Q) components.

4. The receiver of claim 3, wherein the complex notch filter includes positive and negative I inputs, positive and negative I outputs, positive and negative Q inputs, and positive and negative Q outputs.

5. The receiver of claim 4, wherein a first one of the resistors is coupled between the positive I input and the positive I output, a second one of the resistors is coupled between the negative I input and the negative I output, a third one of the resistors is coupled between the positive Q input and the positive Q output, and a fourth one of the resistors is coupled between the negative Q input and the negative Q output.

6. The receiver of claim 5, wherein a first one of the capacitors is coupled between the positive I input and the positive Q output, a second one of the capacitors is coupled between the negative I input and the negative Q output, a third one of the capacitors is coupled between the positive Q input and the negative I output, and a fourth one of the capacitors is coupled between the negative Q input and the positive I output.

7. The receiver of claim 6, wherein the resistors and capacitors have values selected such that the complex filter substantially attenuates the down-converted signal at approximately a frequency of the down-converted transmit leakage signal.

8. The receiver of claim 7, wherein the mixer down-converts a component of the amplified signal corresponding to the desired signal to approximately 0 Hz, and down-converts a component of the amplified signal corresponding to the transmit leakage signal to an offset frequency.

9. The receiver of claim 8, wherein the offset frequency is one of approximately 80 MHz or approximately 45 MHz.

10. The receiver of claim 1, further comprising an antenna that receives the desired signal, a duplexer that couples the amplifier to the antenna, a baseband filter that filters an output of the notch filter, and a modem that demodulates an output of the baseband filter.

11. The receiver of claim 1, wherein the notch filter comprises a complex notch filter comprising resistors and capacitors arranged such that the complex filter substantially attenuates the down-converted signal at approximately a frequency of the transmit leakage signal.

12. A notch filter for a radio frequency (RF) receiver, the notch filter comprising:

a first resistor coupled between a positive in-phase (I) input and a positive I output;

a second resistor coupled between a negative I input and a negative I output;

a third resistor coupled between a positive quadrature (Q) input and a positive Q output;

a fourth resistor coupled between a negative Q input and a negative Q output;

a first capacitor coupled between the positive I input and the positive Q output;

a second capacitor coupled between the negative I input and the negative Q output;

a third capacitor coupled between the positive Q input and the negative I output; and

a

fourth capacitor coupled between the negative Q input and the positive I output,

wherein the resistor and capacitor values are selected to substantially reduce a down-converted transmit leakage signal in an input signal applied at the inputs.

13. The notch filter of claim 12, wherein the notch filter is coupled to receive the down-converted signal from a passive mixer.

14. The notch filter of claim 13, wherein the mixer down-converts a component of the amplified signal corresponding to a desired signal to approximately 0 Hz, and down-converts a component of the amplified signal corresponding to the transmit leakage signal to an offset frequency, the resistor and capacitor values being selected to substantially attenuate the down-converted signal at approximately the offset frequency.

15. The notch filter of claim 14, wherein the offset frequency is one of approximately 80 MHz or approximately 45 MHz.

16. A wireless communication device comprising:

an antenna;

a radio frequency (RF) transmitter that generates a transmit (TX) signal;

a duplexer that couples the TX signal to the antenna;

an RF receiver that receives an RF input signal from the antenna via the duplexer, wherein the RF receiver comprises;

an amplifier that amplifies the received RF input signal comprising a desired signal and a transmit leakage signal coupled from the duplexer;

a mixer that down-converts the amplified signal; and

a notch filter that filters the down-converted signal to substantially reduce the down-converted transmit leakage signal, the notch filter having a notch frequency substantially equal to an offset frequency of the down-converted transmit leakage signal relative to the down-converted desired signal.

17. The device of claim 16, wherein the mixer comprises a passive mixer, and the notch filter comprises a complex notch filter comprising an arrangement of resistors and capacitors.

18. The device of claim 17, wherein the amplifier and the mixer comprise differential outputs, the mixer generating positive and negative in-phase (I) components and positive and negative quadrature (Q) components.

19. The device of claim 18, wherein the complex notch filter includes positive and negative I inputs, positive and negative I outputs, positive and negative Q inputs, and positive and negative Q outputs.

20. The device of claim 19, wherein a first one of the resistors is coupled between the positive I input and the positive I output, a second one of the resistors is coupled between the negative I input and the negative I output, a third one of the resistors is coupled between the positive Q input and the positive Q output, and a fourth one of the resistors is coupled between the negative Q input and the negative Q output.

21. The device of claim 20, wherein a first one of the capacitors is coupled between the positive I input and the positive Q output, a second one of the capacitors is coupled between the negative I input and the negative Q output, a third one of the capacitors is coupled between the positive Q input and the negative I output, and a fourth one of the capacitors is coupled between the negative Q input and the positive I output.

22. The device of claim 21, wherein the resistors and capacitors have values selected such that the complex filter substantially attenuates the down-converted signal at approximately a frequency of the transmit leakage signal.

23. The device of claim 22, wherein the mixer down-converts a component of the amplified signal corresponding to the desired signal to approximately 0 Hz, and down-converts a component of the amplified signal corresponding to the transmit leakage signal to an offset frequency.

24. The device of claim 23, wherein the offset frequency is one of approximately 80 MHz or approximately 45 MHz.

25. The device of claim 16, wherein the notch filter comprises a complex notch filter comprising resistors and capacitors arranged such that the complex filter substantially attenuates the down-converted signal at approximately a frequency of the transmit leakage signal.

26. A method comprising:

amplifying a received RF input signal comprising a desired signal and a transmit leakage signal;

down-converting a frequency of the amplified signal; and

filtering the down-converted signal with a notch filter having a notch frequency substantially equal to an offset frequency of the down-converted transmit leakage signal relative to the down-converted desired signal to substantially reduce the down-converted transmit leakage signal.

27. The method of claim 26, further comprising down-converting the frequency of the amplified signal with a passive mixer, wherein the notch filter comprises a complex notch filter comprising an arrangement of resistors and capacitors.

28. The method of claim 27, wherein the passive mixer generates positive and negative in-phase (I) components and positive and negative quadrature (Q) components.

29. The method of claim 28, wherein the complex notch filter includes positive and negative I inputs, positive and negative I outputs, positive and negative Q inputs, and positive and negative Q outputs.

30. The method of claim 29, wherein a first one of the resistors is coupled between the positive I input and the positive I output, a second one of the resistors is coupled between the negative I input and the negative I output, a third one of the resistors is coupled between the positive Q input and the positive Q output, and a fourth one of the resistors is coupled between the negative Q input and the negative Q output.

31. The method of claim 30, wherein a first one of the capacitors is coupled between the positive I input and the positive Q output, a second one of the capacitors is coupled between the negative I input and the negative Q output, a third one of the capacitors is coupled between the positive Q input and the negative I output, and a fourth one of the capacitors is coupled between the negative Q input and the positive I output.

32. The method of claim 31, wherein the resistors and capacitors have values selected such that the complex filter substantially attenuates the down-converted signal at approximately a frequency of the transmit leakage signal.

33. The method of claim 32, wherein down-converting comprises down-converting a component of the amplified signal corresponding to the desired signal to approximately 0 Hz, and down-converting a component of the amplified signal corresponding to the transmit leakage signal to an offset frequency.

34. The method of claim 33, wherein the offset frequency is one of approximately 80 MHz or approximately 45 MHz.

35. The method of claim 26, further comprising receiving the desired signal via an antenna, and receiving the transmit leakage signal via a duplexer coupled to the antenna and to a transmitter.

36. The method of claim 26, wherein the notch filter comprises a complex notch filter comprising resistors and capacitors arranged such that the complex filter substantially attenuates the down-converted signal at approximately a frequency of the distortion caused by the transmit leakage signal.