Active cancellation of transmitter leakage in a wireless transceiver

• US 8,175,535 B2
• Filed: 02/27/2008
• Issued: 05/08/2012
• Est. Priority Date: 02/27/2008
• Status: Expired due to Fees

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Mu, Fenghao
• Primary Examiner(s): Nguyen, Simon
• Application Number:
  US12/038,487
• Publication Number:
  US 20090213770A1
• Time in Patent Office: 1,532 Days
• Field of Search: 455/63.1, 455/67.11, 455/67.13, 455/295, 455/296, 455283-285, 455302-305, 455/114.2
• US Class Current: 455/67.11
• CPC Class Codes: H03F 1/02 Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H04B 1/123 using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H
• CPC Class Codes: H04B 1/126 having multiple inputs, e.g. auxiliary antenna for receiving interfering signal aerials in general H01Q
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver
• CPC Class Codes: H04B 2001/045 with means for improving efficiency

Abstract

Active transmitter leakage cancellation techniques are disclosed, for reducing transmitter leakage in a frequency-duplexing radio transceiver. Reducing transmitter leakage to the receiver path of a duplex transceiver eases the linearity requirements for low-noise amplifier and mixer circuits, potentially reducing transceiver cost as well as complexity. In an exemplary method, a radio-frequency (RF) cancellation signal is generated from a transmitter signal, and the RF cancellation signal is combined with a received RF signal to obtain a combined RF signal comprising a residual transmitter leakage component. The residual transmitter leakage component of the combined RF signal is converted, using, e.g., a frequency mixer, to obtain a down-converted signal at baseband or at an intermediate frequency. A magnitude of the residual transmitter leakage component is detected from the down-converted signal, and used to adjust the phase or amplitude of the RF cancellation signal, or both, to reduce the residual transmitter leakage component.

Claims

1. A method of cancelling transmitter leakage in a primary receiver path of a frequency-duplexing transceiver, comprising:

generating a radio-frequency (RF) cancellation signal from a transmitter signal;

combining the RF cancellation signal with a received RF signal to obtain a combined RF signal comprising a residual transmitter leakage component;

converting, in a secondary receiver path, the residual transmitter leakage component of the combined RF signal to a down-converted signal by mixing, in the secondary path, the combined RF signal with a local oscillator signal at a first frequency where the transmitter signal is centered;

detecting, in the secondary receiver path, a magnitude of the residual transmitter leakage component from the down-converted signal;

obtaining a phase or amplitude adjustment, or both, based on the detected magnitude; and

applying the phase or amplitude adjustment, or both, to the RF cancellation signal to reduce the residual transmitter leakage component.

2. The method of claim 1, wherein generating an RF cancellation signal from a transmitter signal comprises coupling the transmitter signal from a transmitter section of the transceiver, from a point prior to final amplification of the transmitter signal.

3. The method of claim 1, wherein combining the RF cancellation signal with a received RF signal comprises injecting the RF cancellation signal at the input of a low-noise amplifier circuit, so that the output of the low-noise amplifier circuit comprises the combined RF signal.

4. The method of claim 1, wherein combining the RF cancellation signal with a received RF signal comprises combining the RF cancellation signal with the output of a low-noise amplifier circuit configured to amplify the received RF signal, prior to said converting.

5. The method of claim 1, wherein detecting the magnitude of the residual transmitter leakage component from the down-converted signal comprises rectifying the down-converted signal and filtering the rectified down-converted signal with a low-pass filter.

6. The method of claim 1, wherein the received RF signal is centered at a second frequency, and wherein converting the residual transmitter leakage component of the combined RF signal to a down-converted signal comprises mixing the combined RF signal with a local oscillator signal at the second frequency to convert the residual transmitter leakage component to the intermediate frequency.

7. The method of claim 6, further comprising filtering the residual transmitter leakage component at the intermediate frequency prior to detecting the magnitude of the residual transmitter leakage component.

8. The method of claim 1, wherein obtaining the phase or amplitude adjustment, or both, based on the detected magnitude, and applying the phase or amplitude adjustment, or both, to the RF cancellation signal to reduce the residual transmitter leakage component, comprises:

while holding the amplitude of the RF cancellation signal constant at a first amplitude, varying the phase of the RF cancellation signal to determine an adjusted phase corresponding to a minimum level of the detected magnitude for the first amplitude; and

while holding the phase of the RF cancellation signal constant at the adjusted phase, varying the amplitude of the RF cancellation signal to determine an adjusted amplitude corresponding to a minimum level of the detected magnitude for the adjusted phase.

9. The method of claim 1, wherein obtaining the phase or amplitude-adjustment, or both, based on the detected magnitude, and applying the phase or amplitude adjustment, or both, to the RF cancellation signal to reduce the residual transmitter leakage component, comprises:

while holding the phase of the RF cancellation signal constant at a first phase, varying the amplitude of the RF cancellation signal to determine an adjusted amplitude corresponding to a minimum level of the detected magnitude for the first phase; and

while holding the amplitude of the RF cancellation signal constant at the adjusted amplitude, varying the phase of the RF cancellation signal to determine an adjusted phase corresponding to a minimum level of the detected magnitude for the adjusted amplitude.

10. A frequency-duplexing transceiver comprising:

a transmitter section configured to produce a transmitter signal at a first frequency;

a front-end section configured to combine a received radio-frequency (RF) signal with an RF cancellation signal to obtain a combined RF signal comprising a residual transmitter leakage component resulting from leakage to the front-end section from the transmitter section;

a frequency mixer coupled to the front-end section and configured to convert, in a secondary receiver path, the residual transmitter leakage component of the combined RF signal to a down-converted signal by mixing, in the secondary receiver path, the combined RF signal with a local oscillator signal at the first frequency;

a leakage detector section coupled to the frequency mixer and configured to detect, in the secondary receiver path, a magnitude of the residual transmitter leakage component from the down-converted signal; and

a leakage cancellation section coupled to the leakage detector section, the transmitter section, and the front-end section, and configured to couple the transmitter signal from the transmitter to generate the RF cancellation signal, and to obtain a phase or amplitude adjustment, or both, based on the detected magnitude, and to apply the phase or amplitude adjustment, or both, to the RF cancellation signal, to reduce the residual transmitter leakage component in a primary receiver path.

11. The frequency-duplexing transceiver of claim 10, wherein the leakage cancellation section couples the transmitter signal from the transmitter section at a point prior to final amplification of the transmitter signal.

12. The frequency-duplexing transceiver of claim 10, wherein the front-end section comprises a low-noise amplifier circuit configured to amplify the received RF signal, and wherein the RF cancellation signal is injected at the input of the low-noise amplifier circuit so that the output of the low-noise amplifier circuit comprises the combined RF signal.

13. The frequency-duplexing transceiver of claim 10, wherein the front-end section comprises a low-noise amplifier circuit configured to amplify the received RF signal, and wherein the RF cancellation signal is combined with the output of the low-noise amplifier circuit to obtain the combined RF signal.

14. The frequency-duplexing transceiver of claim 10, wherein the leakage detector section comprises a rectifier configured to detect the envelope of the residual transmitter leakage component, a low-pass filter configured to filter the detected envelope, and a analog-to-digital converter configured to sample the filter output to obtain the magnitude of the residual leakage component.

15. The frequency-duplexing transceiver of claim 10, wherein the received RF signal is centered at a second frequency, and wherein the frequency mixer comprises a mixer circuit configured to mix the combined RF signal with a local oscillator signal at the second frequency to convert the residual transmitter leakage component to the down-converted signal at the intermediate frequency.

16. The frequency-duplexing transceiver of claim 15, wherein the frequency mixer further comprises an intermediate frequency filter configured to filter the output of the mixer circuit to obtain the down-converted signal.

17. The frequency-duplexing transceiver of claim 10, wherein the leakage cancellation section comprises a phase and amplitude modulator circuit for independently adjusting the phase and amplitude of the RF cancellation signal and processing circuitry for controlling the phase and amplitude modulator circuit based on the detected magnitude of the residual transmitter leakage component.

18. The frequency-duplexing transceiver of claim 17, wherein the leakage cancellation section further comprises a variable attenuator configured to provide two or more levels of attenuation of the RF cancellation signal under the control of the processing circuit.