Clock data recovery with decision feedback equalization
Methods and systems are described for generating two comparator outputs by comparing a received signal to a first threshold and a second threshold according to a sampling clock, the first and second thresholds determined by an estimated amount of inter-symbol interference on a multi-wire bus, selecting one of the two comparator outputs as a data decision, the selection based on at least one prior data decision, and selecting one of the two comparator outputs as a phase-error indication, the phase error indication selected in response to identification of a predetermined data decision pattern.
1. A method comprising:
generating a received signal using a sub-channel detection multi-input comparator (MIC) operating on signals received via a plurality of wires, the signals received via the plurality of wires correspond to symbols of a codeword of a vector signaling code, the codeword corresponding to a weighted summation of a plurality of sub-channel vectors, each sub-channel vector mutually orthogonal;
generating two comparator outputs at a single sampling point by comparing the received signal to a first threshold and a second threshold according to a sampling clock, the first and second thresholds associated with sub-channel specific inter-symbol interference on a multi-wire bus;
selecting one of the two comparator outputs as a data decision, the selection based on at least one prior data decision; and
selecting one of the two comparator outputs as a phase-error indication to be provided to a clock recovery circuit generating the sampling clock in response to an identification of a predetermined data decision pattern.
2. The method of claim 1 , further comprising adjusting a phase of the sampling clock according to the phase-error indication.
3. The method of claim 2 , wherein the phase-error indication is an early/late logic decision on a transition of the received signal.
4. The method of claim 1 , further comprising generating the first and second thresholds using a decision-feedback equalization (DFE) circuit.
5. The method of claim 4 , wherein the first and second thresholds correspond to speculative DFE thresholds.
6. The method of claim 1 , wherein the sub-channel specific ISI corresponds to modulation of components of a corresponding sub-channel vector associated with the received signal.
7. The method of claim 6 , wherein sub-channel specific ISI associated with each sub-channel vector is mutually orthogonal.
8. The method of claim 1 , further comprising filtering the received signal prior to generating the two comparator outputs.
9. An apparatus comprising:
a sub-channel detection multi-input comparator (MIC) operating on signals received via a plurality of wires, the sub-channel detection MIC configured to generate a received signal, wherein the signals received via the plurality of wires correspond to symbols of a codeword of a vector signaling code, the codeword corresponding to a weighted summation of a plurality of sub-channel vectors, each sub-channel vector mutually orthogonal;
two comparators configured to generate two comparator outputs at a single sampling time, the two comparators configured to compare the received signal to a first threshold and a second threshold according to a sampling clock, the first and second thresholds associated with sub-channel specific inter-symbol interference on a multi-wire bus;
a data decision selection circuit configured to select one of the two comparator outputs as a data decision, the selection based on at least one prior data decision; and
a phase-error indication selection circuit configured to select one of the two comparator outputs in response to receiving a selection signal from a pattern detection circuit configured to identify a predetermined data decision pattern, and to responsively provide the selected comparator output to a clock recovery circuit as a phase-error indication.
10. The apparatus of claim 9 , further comprising a receiver clock system configured to receive the phase-error indication and to responsively adjust a phase of the sampling clock.
11. The apparatus of claim 10 , wherein the phase-error indication is an early/late logic decision on a transition of the received signal.
12. The apparatus of claim 9 , further comprising a decision-feedback equalization (DFE) circuit configured to generate the first and second thresholds.
13. The apparatus of claim 12 , wherein the first and second thresholds are speculative DFE thresholds.
14. The apparatus of claim 9 , wherein the sub-channel specific ISI corresponds to modulation of components of a corresponding sub-channel vector associated with the received signal.
15. The apparatus of claim 14 , wherein sub-channel specific ISI associated with each sub-channel vector is mutually orthogonal.
16. The apparatus of claim 9 , further comprising a filter configured to filter the received signal prior to generating the two comparator outputs.