Phase tracking system
View Patent ↗A phase tracking system includes a source of an input signal representing a received symbol. A phase rotator has a first input terminal which is responsive to the input signal, a second input terminal which is responsive to a phase correction signal, and an output terminal which produces a phase adjusted output signal. A decision element generates an ideal signal representing the received symbol in response to the phase adjusted output signal. A phase adjuster, which has full phase wrap-around capability, generates the phase correction signal in response to the phase difference between the phase adjusted output signal and the ideal signal.
1. A phase tracking system, comprising:
a source of an input signal representing a received symbol;
a phase rotator, having a first input terminal responsive to the input signal, a second input terminal responsive to a phase correction signal, and an output terminal producing a phase adjusted output signal;
a decision element, responsive to the phase adjusted output signal, for generating an ideal signal representing the received symbol; and
a phase adjuster, for generating the phase correction signal responsive to the phase difference between the ideal signal and the phase adjusted output signal, wherein the phase adjuster has full phase wrap-around capability and comprises a phase limiter for limiting the phase correction signal to within a specified range.
2. The system of claim 1 wherein the phase adjuster is 180° phase rotation invariant.
3. The system of claim 2 further comprising:
a polarity detector, responsive to the phase difference, for generating a control signal having a first state when the phase adjuster is locked to the positive real axis and a second state when the phase adjuster is locked to the negative real axis; and
a polarity corrector, for generating a corrected phase adjusted output signal responsive to the phase adjusted output signal and the control signal.
4. The system of claim 3 further wherein the polarity corrector is configured to generate the corrected phase adjusted output signal by negating the phase adjusted output signal when the control signal is in the second state and passing the phase adjusted output signal unchanged when the control signal is in the first state.
5. The system of claim 1 wherein the phase rotator comprises a complex multiplier having a first complex input terminal responsive to the input signal, a second complex input terminal responsive to the phase correction signal and a complex output terminal producing the phase adjusted output signal.
6. The system of claim 5 wherein:
the input signal comprises only a real component;
the system further comprises a Hilbert filter, responsive to the real component of the input signal, for generating a signal representing an estimation of an imaginary component of the input signal; and
the first complex input terminal of the complex multiplier comprises a real input terminal coupled to the input signal source and an imaginary input terminal coupled to the Hilbert filter.
7. The system of claim 5 wherein:
the complex multiplier produces the phase adjusted output signal as a complex signal having a real and an imaginary component;
the decision element generates an ideal signal having only a real component in response to the real component of the phase adjusted output signal; and
the phase adjuster comprises:
a phase detector, coupled to the phase rotator and the decision element, for:
estimating the phase of the phase adjusted output signal from the real and imaginary components of the output signal from the complex multiplier;
estimating the phase of the idea signal from the real component of the ideal signal; and
estimating the phase difference between the ideal signal and the phase of the phase adjusted output signal; and
a phase corrector, for generating the phase correction signal responsive to the phase difference.
8. The system of claim 7 wherein the phase adjuster further comprises an accumulator for accumulating the phase difference.
9. The system of claim 7 wherein the phase corrector comprises a sine/cosine generator, having a full ±180° capability, responsive to the phase difference, for generating the complex phase correction signal.
10. The system of claim 9 wherein the phase adjuster further comprises an accumulator for accumulating the phase difference wherein the maximum value of the accumulator corresponds to +180° and the minimum value of the accumulator corresponds to −180°.
11. The system of claim 1 wherein the phase adjuster comprises:
a phase detector, coupled to the phase rotator and the decision element, for detecting the phase difference between the ideal signal and the phase adjusted output signal; and
a phase corrector, for generating the phase correction signal responsive to the phase difference.
12. The system of claim 11 wherein the phase detector further comprises an accumulator for accumulating successive phase differences.
13. The system of claim 12 wherein the phase corrector comprises a sine/cosine generator having a full ±180° range for generating the phase correction signal in response to the accumulated phase differences; and
the accumulator has a maximum value associated with the +180° entry in the sine/cosine generator and a minimum value associated with the −180° entry in the sine/cosine generator.
14. The system of claim 13 wherein the sine/cosine generator comprises a look-up table having a full ±180° range.
15. The system of claim 1 wherein said input signal is a high definition television VSB modulated signal in accordance with the ATSC standard.
16. The system of claim 1 wherein said input signal is modulated by a one-dimensional modulation technique.
17. The system of claim 1 wherein the phase limiter limits the phase correction signal to within one or more specified ranges around the following angles: 0 degrees and 180 degrees.
18. The system of claim 1 , wherein the phase adjuster limits phase adjustments to within the specified range while accumulating phase error greater than the specified range.
19. A method comprising:
receiving an input signal representing a received symbol;
rotating the input signal based on a phase correction signal to produce a phase adjusted output signal;
generating, based on the phase adjusted output signal, an ideal signal representing the received symbol; and
generating a phase correction signal based on a phase difference between the ideal signal and the phase adjusted output signal, wherein a phase adjuster is used to generate the phase correction signal and the phase adjuster has full phase wrap-around capability, and wherein generating the phase correction signal comprises limiting the phase correction signal to within a specified range.
20. The method of claim 19 further comprising:
generating a control signal having a first state when the phase adjuster is locked to the positive real axis and a second state when the phase adjuster is locked to the negative real axis; and
generating a corrected phase adjusted output signal responsive to the phase adjusted output signal and the control signal.
21. The method of claim 20 wherein generating the corrected phase adjusted output signal comprises negating the phase adjusted output signal when the control signal is in the second state and passing the phase adjusted output signal unchanged when the control signal is in the first state.
22. The method of claim 19 wherein limiting the phase correction signal comprises limiting the phase correction signal to within one or more specified ranges around the following angles: 0 degrees and 180 degrees.
23. The method of claim 19 wherein generating the phase correction signal comprises:
estimating phase of the phase adjusted output signal from real and imaginary components of the phase adjusted output signal;
estimating phase of the ideal signal from a real component of the ideal signal;
estimating phase difference between the ideal signal and the phase of the phase adjusted output signal; and
generating the phase correction signal responsive to the phase difference between the ideal signal and the phase of the phase adjusted output signal.
24. The method of claim 19 , wherein the phase adjuster limits phase adjustments to within the specified range while accumulating phase errors greater than the specified range.