Adaptive equalization using correlation of data patterns with errors
An integrated receiver supports adaptive receive equalization. An incoming bit stream is sampled using edge and data clock signals derived from a reference clock signal. A phase detector determines whether the edge and data clock signals are in phase with the incoming data, while some clock recovery circuitry adjusts the edge and data clock signals as required to match their phases to the incoming data. The receiver employs the edge and data samples used to recover the edge and data clock signals to note the locations of zero crossings for one or more selected data patterns. The pattern or patterns may be selected from among those apt to produce the greatest timing error. Equalization settings may then be adjusted to align the zero crossings of the selected data patterns with the recovered edge clock signal.
1. A receiver comprising:
a receive port to receive a distorted signal expressing a series of symbols;
an equalizer coupled to the receive port to equalize the distorted signal, responsive to an equalizer control signal, to thereby create an equalized signal;
a least one sampler to sample the equalized signal and thereby recover the series of symbols as a sampled signal; and
equalizer control circuitry to adjust the equalizer control signal responsive to the sampled signal, the equalizer control circuitry including:
a pattern mask to compare the sampled signal with different patterns;
a detector to detect errors in the sampled signal; and
equalization logic to correlate each of the different patterns with the errors, the equalization logic to adjust the equalizer control signal responsive to the errors correlated with the different patterns.
2. The receiver of claim 1 , wherein a first of the different patterns represents high-frequency components and a second of the different patterns represents low-frequency components.
3. The receiver of claim 2 , wherein the equalizer control circuitry adjusts the equalizer control signal responsive to a ratio of the errors correlated with the high-frequency components to the errors correlated with the low-frequency components.
4. The receiver of claim 1 , further comprising counters to accumulate a number of the errors correlated with each of the different patterns.
5. The receiver of claim 4 , wherein the number of the counters equals the number of the different patterns.
6. The receiver of claim 1 , wherein the detector to detect the errors comprises a phase detector.
7. The receiver of claim 1 , wherein the at least one sampler includes a data sampler and an error sampler.
8. The receiver of claim 1 , the pattern mask including a data register to store the sampled signal and a pattern register to store the different patterns.
9. A method of equalizing a distorted signal expressing a series of symbols, the method comprising:
equalizing the distorted signal to create an equalized signal;
sampling the equalized signal to recover the series of symbols as a sampled signal; and
detecting errors in the sampled signal;
comparing the sampled signal with different patterns;
finding correlations between the errors and the different patterns; and
adjusting the equalizing of the distorted signal responsive to the correlations.
10. The method of claim 9 , wherein a first of the different patterns represents high-frequency components and a second of the different patterns represents low-frequency components.
11. The method of claim 10 , wherein adjusting the equalizing considers a ratio of the errors correlated with the high-frequency components to the errors correlated with the low-frequency components.
12. The method of claim 9 , further comprising accumulating a number of the errors correlated with each of the different patterns.
13. The method of claim 9 , wherein detecting errors comprises detecting a phase of the equalized signal.
14. The method of claim 13 , wherein detecting the phase comprises sampling edges of the equalized signal.
15. The method of claim 14 , further comprising recovering a clock signal from at least one of the distorted signal and the equalized signal.
16. The method of claim 15 , further comprising sampling the edges of the equalized signal using the clock signal.
17. An integrated circuit comprising:
a receive port to receive a distorted signal expressing a series of symbols;
an equalizer coupled to the receive port to equalize the distorted signal to thereby create an equalized signal;
a least one sampler to sample the equalized signal and thereby recover the series of symbols as a sampled signal; and
means for correlating a first pattern of the series of symbols with first errors in the series of symbols and a second pattern of the series of symbols with second errors in the series of symbols; and
means for adjusting a low-frequency gain of the equalizer responsive to the first errors and a high-frequency gain of the equalizer responsive to the second errors.
18. The integrated circuit of claim 17 , further comprising a first counter to count the first errors in the series of symbols and a second counter to count the second errors in the series of symbols.
19. The integrated circuit of claim 17 , further comprising a phase detector to detect at least one of the first errors and the second errors.
20. The integrated circuit of claim 17 , the at least one sampler comprising a data sampler to recover the series of symbols and an edge sampler to sample edges of at least one of the distorted signal and the equalized signal to sample the first errors and the second errors.