Multiple-tap compensation and calibration
Corrections are provided for mismatches between an in-phase (I) signal and a quadrature-phase (Q) signal, the I and Q signals having a first frequency band. A frequency filter circuit filters the I and Q signals to produce a filtered I and Q output with a second frequency band that is a subset of the first frequency band. Digital circuitry includes a multiple-tap correction filter having a plurality of taps and configured to generate I and Q output signals by filtering the I and Q signals according to respective sets of coefficients for the plurality of taps. A coefficient estimator generates the sets of coefficients relative to different frequency bands.
1. An apparatus to correct for mismatches between an in-phase (I) signal and a quadrature-phase (Q) signal, the I and Q signals having a first frequency band, the apparatus comprising:
a frequency filter circuit configured to filter the I and Q signals to produce a filtered I and Q output with a second frequency band that is a subset of the first frequency band, wherein the second frequency band falls entirely within the first frequency band and spans less than the first frequency band;
digital circuitry that includes:
a multiple tap correction filter having a plurality of taps and configured to generate I and Q output signals by filtering the I and Q signals according to respective sets of coefficients for the plurality of taps;
a coefficient estimator configured to
generate, from the I and Q signals having the first frequency band,
a first set of coefficients for the sets of coefficients; and
generate, from the filtered I and Q signals having the second frequency band, second and third sets of coefficients for the sets of coefficients.
2. The apparatus of claim 1 , wherein each set of coefficients includes a phase component and a gain component, wherein the coefficient estimator is further configured to generate respective phase components by determining a phase correlation between I and Q signals and integrating the determined phase correlation.
3. The apparatus of claim 2 , wherein the coefficient estimator is further configured to generate respective gain components by determining an absolute difference in amplitude of I and Q signals and integrating the determined absolute difference.
4. The apparatus of claim 1 , wherein the second frequency band is half of the first frequency band, wherein the multiple tap correction filter is configured to provide the I and Q signals having the first frequency band and the I and Q signals having the second frequency band to the coefficient estimator, and provide the I and Q signals having the first frequency band as an output for decoding data within the I and Q signals.
5. The apparatus of claim 4 , wherein the coefficient estimator is further configured to generate, from the filtered I and Q signals having the second frequency band, a single phase component and a single gain component that is used for sets of coefficients one both sides of at tap corresponding to the first set of coefficients.
6. The apparatus of claim 1 , further comprising an analog-to-digital converter (ADC) circuit configured to convert the I and Q signals to a digital signal that is provided to the frequency filter circuit.
7. The apparatus of claim 6 , further comprising a surface acoustic wave filter configured to filter the I and Q signals according to the first frequency band and to provide an output to the ADC.
8. The apparatus of claim 1 , wherein the digital circuitry is part of a digital signal processor (DSP), wherein the coefficient estimator is configured to provide the first set of coefficients and the second set of coefficients to the multiple tap correction filter.
9. The apparatus of claim 1 , wherein the multiple tap correction filter includes:
a first multiple tap correction filter configured to:
generate I and Q output signals having the first frequency band by filtering the I and Q signals according to respective sets of coefficients for a plurality of taps; and
provide the I and Q signals having the first frequency band to the coefficient estimator, and as an output for decoding data within the I and Q signals;
a second multiple tape correction filter configured to:
generate I and Q output signals having the second frequency band by filtering the I and Q signals according to respective sets of coefficients for a plurality of taps; and
provide the I and Q signals having the second frequency band to the coefficient estimator.
10. The apparatus of claim 9 , wherein each of the first and second multiple tap correction filters includes three taps;
the coefficient estimator is further configured to provide the first set of coefficients and the second set of coefficients to the first multiple tap correction filter and the second multiple tap correction filter; and
the first multiple tap correction filter and the second multiple tap correction filter are further configured to use the first set of coefficients as a center tap of the three taps and use the second set of coefficients as first and third taps of the three taps.
11. A method comprising:
receiving an in-phase (I) signal and a quadrature-phase (Q) signal having a first frequency bandwidth;
correcting, using a multiple-tap correction filter having a plurality of taps, mismatches in the I and Q signals by filtering the I and Q signals according to sets of coefficients for the plurality of taps;
filtering the I and Q signals to produce filtered I and Q signals having a second frequency bandwidth that is a subset of the first frequency bandwidth, wherein the second frequency bandwidth falls entirely within the first frequency bandwidth and spans less than the first frequency bandwidth;
correcting, using the multiple-tap correction filter, mismatches in the filtered I and Q signals by filtering the filtered I and Q output according to the respective sets of coefficients;
generating, from the corrected I and Q signals having the first frequency bandwidth, a first set of coefficients for the sets of coefficients; and
generating, from the corrected I and Q signals having the second frequency bandwidth, second and third sets of coefficients for the sets of coefficients.
12. The method of claim 11 , wherein each set of coefficients includes a phase component and a gain component.
13. The method of claim 12 , further comprising generating respective phase components by determining a phase correlation between respective I and Q signals and integrating the determined phase correlation.
14. The method of claim 12 , further comprising generating respective gain components by determining an absolute difference in amplitude of respective I and Q signals and integrating the determined amplitude.
15. The method of claim 11 , wherein the second frequency bandwidth is half of the first frequency bandwidth.
16. The method of claim 15 , further comprising generating a single phase component and a single gain component for different sets of coefficients on both sides of the first set of coefficients.
17. The method of claim 11 , further comprising converting the I and Q signals to digital signals before the filtering to produce the filtered I and Q signals.
18. The method of claim 17 , further comprising filtering the I and Q signals using a surface acoustic wave filter configured as a bandpass filter corresponding to the first frequency bandwidth.
19. The method of claim 11 , wherein the generating the second set of coefficients occurs during an initialization phase using a coefficient estimator and the generating the first set of coefficients occurs during a subsequent phase using the same coefficient estimator.
20. The method of claim 19 , further comprising using time-interleaving to use the coefficient estimator to generate the first and second set of coefficients.