DC offset cancellation

Abstract

A transmitter has a transmission path with an IQ modulator and a feedback path with an IQ demodulator. DC offset is determined by estimating a DC offset of the IQ demodulator, adaptively estimating a DC offset of the IQ modulator at least partially from the demodulator DC offset, subtracting the estimated demodulator DC offset from the feedback path and subtracting the estimated modulator DC offset from the transmission path.

1 . A method of adaptively estimating a DC offset of an IQ modulator, the method comprising: 
 providing a predetermined signal to an input of said IQ modulator and transmitting said signal;    estimating a DC offset of an IQ demodulator from a received version of said signal;    generating a difference signal between said received signal and said estimated DC offset of said IQ demodulator; and    subtracting a modified rotated version of said difference signal from a previous value of said DC offset of said IQ modulator.    
   
   
       2 . A method according to  claim 1 , further comprising: 
 estimating a phase rotation of a transmission path of a transmitter and a feedback path of said transmitter; and    modifying said difference signal with said phase rotation.    
   
   
       3 . A method according to  claim 1 , wherein said estimating said DC offset of said IQ demodulator is undertaken during non-transmission slots.  
   
   
       4 . A transmitter comprising: 
 a transmission path having an IQ modulator;    a feedback path having an IQ demodulator;    a demodulator DC offset estimator to average a received signal along said feedback path and to estimate a DC offset of said IQ demodulator; and    an adaptive modulator DC offset estimator to estimate a DC offset of said IQ modulator at least partially from said DC offset of said IQ demodulator, 
 wherein said adaptive modulator DC offset estimator is to generate a difference signal between said received signal and said DC offset of said IQ demodulator and to subtract a modified rotated version of said difference signal from a previous value of said DC offset of said IQ modulator.  
   
   
   
       5 . A transmitter according to  claim 4 , wherein said demodulator DC offset estimator and said adaptive modulator DC offset estimator are to operate during non-transmission slots.  
   
   
       6 . A transmitter according to  claim 5 , wherein said non-transmission slots are non-transmission slots of regular transmission.  
   
   
       7 . A transmitter according to  claim 4 , wherein said adaptive modulator DC offset estimator is to modify said difference signal with a phase rotation of said transmission and feedback paths.  
   
   
       8 . An integrated circuit having a transmitter, the transmitter comprising: 
 a transmission path having an IQ modulator;    a feedback path having an IQ demodulator;    a demodulator DC offset estimator to average a received signal along said feedback path and to estimate a DC offset of said IQ demodulator;    an adaptive modulator DC offset estimator to estimate a DC offset of said IQ modulator by generating a difference signal between said received signal and said demodulator DC offset and subtracting a modified rotated version of said difference signal from a previous value of said DC offset of said IQ modulator.    
   
   
       9 . An integrated circuit according to  claim 8 , wherein said demodulator DC offset estimator and said adaptive modulator DC offset estimator are to operate during non-transmission slots.  
   
   
       10 . An integrated circuit according to  claim 9 , wherein said non-transmission slots are non-transmission slots of regular transmission.  
   
   
       11 . An integrated circuit according to  claim 8 , wherein said adaptive modulator DC offset estimator is to modify said difference signal with a phase rotation of said transmission and feedback paths.