Dual-loop transmit noise cancellation

Abstract

A transmitter circuit is described. The transmitter circuit includes a first local oscillator that generates a first frequency equal to a duplex frequency. The transmitter circuit also includes a second local oscillator that generates a second frequency equal to a receive frequency. The transmitter circuit further includes a first mixer that combines the first frequency with a first input signal. The transmitter circuit also includes a first feedback loop. The first feedback loop includes a second mixer that combines the second frequency with a transmit signal and a first filter and a first adder that combines an output of the first mixer with an output of the first filter. The transmitter circuit also includes a third local oscillator that generates a third frequency equal to the receive frequency. The transmitter circuit further includes a third mixer that combines the third frequency with an output of the first adder.

What is claimed is: 
     
         1 . A method for noise cancellation in a transmit signal, the method comprising:
 estimate transmit noise in the transmit signal that negatively affects a receive signal;   estimate transmit distortion in the transmit signal that negatively affects the fidelity of the transmit signal;   filter estimated transmit noise from the transmit signal;   filter estimated transmit distortion from the transmit signal; and   provide a filtered transmit signal to a duplexer.   
     
     
         2 . The method of  claim 1 , wherein estimating transmit noise and filtering estimated transmit noise comprise:
 mixing a first input signal with a duplex frequency generated by a first local oscillator to obtain a first mixed signal;   combining the first mixed signal with a negative feedback signal to obtain a first combined signal;   mixing the first combined signal with a receive frequency generated by a second local oscillator to obtain a second mixed signal;   applying a plant to the second mixed signal to obtain a transmit signal; and   applying a first feedback loop, wherein applying the first feedback loop comprises:
 mixing the transmit signal with a receive frequency generated by a third local oscillator to obtain a down-converted transmit signal; and 
 filtering the down-converted transmit signal using a first filter to obtain the negative feedback signal. 
   
     
     
         3 . The method of  claim 2 , wherein the plant comprises an upconverter. 
     
     
         4 . The method of  claim 2 , wherein the plant comprises an amplifier. 
     
     
         5 . The method of  claim 2 , wherein estimating transmit distortion and removing transmit distortion comprises applying a second feedback loop, wherein applying the second feedback loop comprises:
 mixing the down-converted transmit signal with a duplex frequency generated by a fourth local oscillator to obtain a third mixed signal;   combining a second input signal with the third mixed signal to obtain a second combined signal; and   filtering the second combined signal using a second filter.   
     
     
         6 . The method of  claim 5 , wherein an output of the second filter is the first input signal. 
     
     
         7 . The method of  claim 5 , wherein the second feedback loop further comprises combining an output of the second filter with the second input signal to obtain a third combined signal. 
     
     
         8 . The method of  claim 7 , wherein the third combined signal is the first input signal. 
     
     
         9 . The method of  claim 2 , wherein the first feedback loop removes estimated transmit noise from the transmit signal. 
     
     
         10 . The method of  claim 5 , wherein the second feedback loop removes estimated transmit distortion from the transmit signal. 
     
     
         11 . The method of  claim 2 , wherein the first input signal comprises an inphase (I) modulated signal and a quadrature (Q) modulated signal. 
     
     
         12 . The method of  claim 5 , wherein the second input signal comprises an inphase (I) modulated signal and a quadrature (Q) modulated signal. 
     
     
         13 . A wireless device configured for noise cancellation in a transmit signal, comprising:
 means for estimating transmit noise in the transmit signal that negatively affects a receive signal;   means for estimating transmit distortion in the transmit signal that negatively affects the fidelity of the transmit signal;   means for filtering estimated transmit noise from the transmit signal;   means for filtering estimated transmit distortion from the transmit signal; and   means for providing a filtered transmit signal to a duplexer.   
     
     
         14 . The wireless device of  claim 13 , wherein the means for estimating transmit noise and the means for filtering estimated transmit noise comprise:
 means for mixing a first input signal with a duplex frequency generated by a first local oscillator to obtain a first mixed signal;   means for combining the first mixed signal with a negative feedback signal to obtain a first combined signal;   means for mixing the first combined signal with a receive frequency generated by a second local oscillator to obtain a second mixed signal;   means for applying a plant to the second mixed signal to obtain a transmit signal; and   means for applying a first feedback loop, wherein applying the first feedback loop comprises:
 means for mixing the transmit signal with a receive frequency generated by a third local oscillator to obtain a down-converted transmit signal; and 
 means for filtering the down-converted transmit signal using a first filter to obtain the negative feedback signal. 
   
     
     
         15 . The wireless device of  claim 14 , wherein the means for estimating transmit distortion and the means for removing transmit distortion comprise means for applying a second feedback loop, wherein the means for applying the second feedback loop comprises:
 means for mixing the down-converted transmit signal with a duplex frequency generated by a fourth local oscillator to obtain a third mixed signal;   means for combining a second input signal with the third mixed signal to obtain a second combined signal; and   means for filtering the second combined signal using a second filter.   
     
     
         16 . A computer-readable medium encoded with computer-executable instructions, wherein execution of the computer-executable instructions is for:
 estimating transmit noise in the transmit signal that negatively affects a receive signal;   estimating transmit distortion in the transmit signal that negatively affects the fidelity of the transmit signal;   filtering estimated transmit noise from the transmit signal;   filtering estimated transmit distortion from the transmit signal; and   providing a filtered transmit signal to a duplexer.   
     
     
         17 . The computer-readable medium of  claim 16 , wherein the instructions for estimating transmit noise and for filtering estimated transmit noise are further executable for:
 mixing a first input signal with a duplex frequency generated by a first local oscillator to obtain a first mixed signal;   combining the first mixed signal with a negative feedback signal to obtain a first combined signal;   mixing the first combined signal with a receive frequency generated by a second local oscillator to obtain a second mixed signal;   applying a plant to the second mixed signal to obtain a transmit signal; and   applying a first feedback loop, wherein applying the first feedback loop comprises:
 mixing the transmit signal with a receive frequency generated by a third local oscillator to obtain a down-converted transmit signal; and 
 filtering the down-converted transmit signal using a first filter to obtain the negative feedback signal. 
   
     
     
         18 . The computer-readable medium of  claim 17 , wherein the instructions for estimating transmit distortion and for removing transmit distortion comprises instructions for applying a second feedback loop, wherein the instructions for applying the second feedback loop are executable for:
 mixing the down-converted transmit signal with a duplex frequency generated by a fourth local oscillator to obtain a third mixed signal;   combining a second input signal with the third mixed signal to obtain a second combined signal; and   filtering the second combined signal using a second filter.