Digital time alignment in a polar modulator

Abstract

Methods of and apparatus for digitally controlling, with sub-sample resolution, the relative timing of the magnitude and phase paths in a polar modulator. The timing resolution is limited by the dynamic range of the system as opposed to the sample rate. The methods and apparatus of the invention use a digital filter to approximate a sub-sample time delay. Various techniques for approximating a sub-sample time delay using digital signal processing may be used to achieve the approximation. Ideally, the filter will have an all-pass magnitude response and a linear phase response. In practice, the magnitude may be low-pass and the phase may not be perfectly linear. Such deviation from the ideal response will introduce some distortion. However, this distortion may be acceptably small depending on the particular signal being processed.

1 - 6 . (canceled)  
   
   
       7 . A method of achieving time alignment between an amplitude path signal and a phase path signal in a modulator having separate amplitude and phase paths, comprising: 
 providing a digital filter within at least one of the amplitude and phase paths; and    adjusting at least one parameter of said digital filter to achieve a time alignment of the amplitude path and phase path signals that is less than or equal to a sample interval associated with said modulator.    
   
   
       8 . (canceled)  
   
   
       9 . The method of  claim 7  wherein said digital filter comprises a linear filter, an IIR filter, an FIR filter, or an all-pass filter.  
   
   
       10 . The method of  claim 7  wherein said digital filter comprises an IIR filter having two or more coefficients.  
   
   
       11 . The method of  claim 7  wherein said digital filter comprises an FIR filter having two or more coefficients.  
   
   
       12 . A transmitter, comprising: 
 separate amplitude and phase paths;    an amplifier responsive to separate amplitude and phase signals for producing a communications signal; and    a digital filter within at least one of the amplitude and phase paths,    wherein adjusting a parameter of the digital filter achieves a relative delay between the amplitude and phase path signals that is less than or equal to a sample interval associated with the digital filter of said transmitter.    
   
   
       13 . (canceled)  
   
   
       14 . The transmitter of  claim 12  wherein said digital filter comprises a linear filter, an IIR filter, an FIR filter, or an all-pass filter.  
   
   
       15 . The transmitter of  claim 12  wherein said digital filter comprises an IIR filter having two or more coefficients.  
   
   
       16 . The transmitter of  claim 12  wherein said digital filter comprises an FIR filter having two or more coefficients.  
   
   
       17 - 26 . (canceled)  
   
   
       27 . A method of achieving time alignment between an amplitude path signal and a phase path signal in a modulator having separate amplitude and phase paths, comprising: 
 providing a digital filter within a first path from among the amplitude path and the phase path;    providing a plurality of values related to a first signal on the first path at a plurality of discrete points in time kT, where k is an integer and T is a time period;    providing, with the digital filter, a value of a second signal corresponding to an estimate of kT+ΔT, where ΔT is an offset in time from a particular kT;    outputting, on the first path, the second signal;    wherein the second signal substantially time aligns a relative delay between the amplitude and phase paths, the relative delay being a proportion of the period T less than 1.    
   
   
       28 . A transmitter comprising: 
 an amplitude path for carrying an amplitude path signal;    a separate phase path for carrying a phase path signal;    an amplifier, responsive to separate amplitude and phase signals, for producing a communications signal;    means for providing a plurality of values related to a first signal on a first path from among the amplitude path and the phase path;    within the first path, means for digitally filtering the first signal, the means for digitally filtering providing an indication of a time-shifted first signal;    the indications comprising values associated with the time-shifted first signal at one or more discrete points in time kT, where k is an integer and T is a sample period associated with the means for digitally filtering;    wherein the time-shifted first signal aligns signals on the amplitude and phase paths at the amplifier to less than a sample period of time mismatch.    
   
   
       29 . An electric circuit comprising: 
 an amplitude path for carrying an amplitude path signal;    a separate phase path for carrying a phase path signal;    within a first path from among the amplitude path and the phase path, a digital filter having an output, the digital filter operable to receive a first signal on the first path, and operable to construct an output signal output on the first path;    the output signal derived from: 
 a plurality of values related to the first signal on the first path at particular discrete points in time kT, where k is an integer and T is a sample period associated with the digital filter;  
 a time offset;  
   wherein the output signal is a time-shifted version of the first signal, the time-shift such that a relative delay between the signal on the phase path and the signal on the amplitude path is less than a time t, where the magnitude of t is less than the magnitude of T.    
   
   
       30 . An electrical circuit comprising: 
 an amplitude path operable to carry an amplitude path signal;    a separate phase path operable to carry a phase path signal;    within a first path from among the amplitude path and the phase path, an interpolating digital filter with an output, the digital filter operable to receive a first signal from among the amplitude path signal and the phase path signal, the digital filter operable to construct a modified first signal on the first path;    the modified first signal dependent upon: 
 a plurality of values related to the first signal on the first path at particular discrete points in time kT, where k is an integer and T is a time period;  
 a time offset;  
   wherein the modified first signal corresponds to an estimate of the first signal at a particular offset from a particular;    wherein a relative time delay between a second signal the path other than the first path and the output signal is less than a sample period associated with the interpolating digital filter.