Vector calibration system

Abstract

Among other things, calibration of a signal processing system is disclosed to minimize vector mismatch between signals frequency-translated from an RF signal and conveyed along a plurality of signal paths of the signal processing system. A calibration signal having a plurality of tones is coupled to the signal processing system such that it is frequency translated. The frequency-translated calibration signal is sampled along a first signal path of the signal processing system to obtain a first set of observed samples. It is also sampled along a second signal path of the system to obtain a second set of observed samples. The first set of observed samples is filtered with an adaptive filter having a set of adaptable coefficients to obtain a set of filtered samples. The coefficients are adapted to minimize undesired deviations between the set of filtered samples and the second set of observed samples.

1 . A method for calibrating a signal processing system to minimize vector mismatch between signals frequency translated from an RF signal and conveyed along a plurality of signal paths of the signal processing system, the method comprising: 
 (a) applying a calibration signal having a plurality of tones to the signal processing system, such that the calibration signal is frequency translated;    (b) sampling the frequency-translated calibration signal (1) along a first signal path of the signal processing system to obtain a first set of observed samples and (2) along a second signal path of the signal processing system to obtain a second set of observed samples;    (c) filtering the first set of observed samples with an adaptive filter having adaptable coefficients to obtain a set of filtered samples; and    (d) adapting the coefficients to minimize undesired deviations between the set of filtered samples and the second set of observed samples.    
   
   
       2 . The method of  claim 1  further comprising using the filter with the adapted coefficients to minimize vector mismatch between signals frequency-translated by the signal processing system from an RF input signal of interest and conveyed along the first and second signal paths.  
   
   
       3 . The method of  claim 1  further comprising generating the calibration signal.  
   
   
       4 . The method of  claim 3  wherein generating the calibration signal comprises: 
 (a) generating a local oscillator signal, which signal the signal processing system uses to perform frequency translation;    (b) generating a baseband calibration signal; and    (c) mixing the local oscillator signal with the baseband calibration signal, thereby obtaining a radio frequency calibration signal.    
   
   
       5 . The method of  claim 1  wherein: 
 (a) the signal paths include an in-phase signal path and a quadrature signal path; and    (b) the filter coefficients are adapted to minimize deviations from a quadrature relationship between a signal on the in-phase signal path and a signal on the quadrature signal path.    
   
   
       6 . The method of  claim 1  wherein: 
 (a) the signal paths include a plurality of signal paths coupled to respective elements of a spatially selective array; and    (b) the filter coefficients are adapted to minimize deviations from a predetermined phase and amplitude relationship between signals on each respective one of the plurality of signal paths, such deviations degrading spatial selectivity of the array.    
   
   
       7 . The method of  claim 6  further comprising generating the calibration signal and transmitting it through an antenna placed at a fixed position with respect to the array elements.  
   
   
       8 . The method of  claim 1  wherein adapting is performed by a least mean squares algorithm.  
   
   
       9 . The method of  claim 8  wherein a plurality of values are determined by least mean squares constrained to a predetermined bounded region.  
   
   
       10 . The method of  claim 1  wherein: 
 (a) the signal paths include an in-phase signal path and a quadrature signal path; and    (b) the filter coefficients are adapted by a least mean squares algorithm to minimize deviations from a quadrature relationship between a signal on the in-phase signal path and a signal on the quadrature signal path.    
   
   
       11 . The method of  claim 10  further comprising: 
 (a) generating the calibration signal; and    (b) after adapting the filter coefficients, using the filter with the adapted coefficients to minimize deviations in a quadrature relationship between in-phase and quadrature signals frequency-translated by the signal processing system from an RF input signal of interest.    
   
   
       12 . A signal processing system comprising: 
 (a) a frequency translation subsystem structured to produce a plurality of frequency-translated signals responsive to a calibration signal having a plurality of tones;    (b) one or more converters coupled to the frequency translation subsystem and structured to convert the signals into a plurality of sets of observed samples;    (c) an adaptive filter having adaptable coefficients and structured to produce a set of filtered samples responsive to one of the sets of observed samples; and    (d) control circuitry structured to adapt the filter coefficients to minimize undesired deviations between the set of filtered samples and a different one of the sets of observed samples.    
   
   
       13 . The system of  claim 12  further comprising a calibration signal subsystem coupled to the frequency translation subsystem and structured to produce the calibration signal.  
   
   
       14 . The system of  claim 12  wherein: 
 (a) the plurality of frequency-translated signals consists of an in-phase signal and a quadrature signal;    (b) the plurality of sets of observed samples consists of two sets of observed samples, one converted from the in-phase signal and the other converted from the quadrature signal; and    (c) the undesired deviations are deviations from a quadrature relationship between the in-phase signal and the quadrature signal.    
   
   
       15 . The system of  claim 12  wherein: 
 (a) the frequency-translated signals are from respective elements of a spatially selective array; and    (b) the undesired deviations are deviations from a predetermined phase and amplitude relationship between signals on each respective one of the plurality of signal paths, such deviations degrading spatial selectivity of the array.    
   
   
       16 . The system of  claim 12  further comprising: 
 (a) a front-end stage structured to produce a selectively amplified RF signal responsive to RF input;    (b) wherein the frequency translation subsystem is further coupled to the front-end stage and structured to produce frequency-translated in-phase and quadrature signals responsive to the selectively amplified RF signal from the front-end stage.    
   
   
       17 . The system of  claim 16  further comprising a switch coupled to the calibration signal subsystem and the front-end stage, and structured to convey a selected one of the calibration signal and the selectively amplified RF signal to the frequency translation subsystem for frequency translation into the in-phase and quadrature signals.  
   
   
       18 . The system of  claim 12  wherein the control circuitry is structured to adapt the filter coefficients by a least mean squares algorithm that determines a plurality of values by least mean squares constrained to a predetermined bounded region.  
   
   
       19 . The system of  claim 12  further comprising: 
 (a) a switch;    (b) a calibration signal subsystem selectably coupled to the frequency translation subsystem via the switch and structured to produce the calibration signal; and    (c) a front-end stage selectably coupled to the frequency translation subsystem via the switch and structured to produce a selectively amplified RF signal responsive to RF input;    (d) wherein the frequency translation subsystem is structured to produce frequency-translated in-phase and quadrature signals responsive to either one of (1) the calibration signal, and (2) the selectively amplified RF signal from the front-end stage.    
   
   
       20 . The system of  claim 19  wherein: 
 (a) the plurality of frequency-translated signals consists of an in-phase signal and a quadrature signal;    (b) the plurality of sets of observed samples consists of two sets of observed samples, one converted from the in-phase signal and the other converted from the quadrature signal; and    (c) the undesired deviations are deviations from a quadrature relationship between the in-phase signal and the quadrature signal.    
   
   
       21 . The system of  claim 20  wherein the control circuitry is structured to adapt the filter coefficients by a least mean squares algorithm that determines a plurality of values by least mean squares constrained to a predetermined bounded region.  
   
   
       22 . A signal processing system comprising: 
 (a) means for generating a calibration signal having a plurality of tones;    (b) means for producing a plurality of frequency-translated signals responsive to the calibration signal;    (c) means for producing filtered samples from one of the frequency-translated signals, using a set of adaptable coefficients; and    (d) means for adapting the filter coefficients to minimize undesired deviations between the filtered samples and a different one of the frequency-translated signals.    
   
   
       23 . The system of  claim 22  further comprising means for receiving and frequency translating an RF input signal to the plurality of frequency-translated signals with undesired deviations between the signals minimized by the adaptation of the filter coefficients.  
   
   
       24 . The system of  claim 22  wherein the plurality of frequency-translated signals consists of an in-phase signal and a quadrature signal and the undesired deviations are deviations from a quadrature relationship between the two signals.  
   
   
       25 . The system of  claim 22  wherein the calibration signal is phase-synchronous with a local oscillator signal employed for producing a plurality of frequency-translated signals responsive to the calibration signal.