System and method for decision feedback equalizer (DFE) adaptation
A system and method for decision feedback equalizer (DFE) tap adaptation. An input signal is received at a DFE of a receiver, wherein the input signal comprises a serial bit stream of encoded symbols. Data samples and error samples are taken from the input signal and the data samples and the error samples are aligned establish a plurality of pairs of data samples and error samples, wherein the data sample and error sample of each of the plurality of pairs of data samples and error samples are from locations in the serial bit stream of encoded symbols that are known to be uncorrelated with each other. The DFE tap weights are then adjusted based upon the plurality of pairs of data samples and error samples.
1. A method for decision feedback equalizer (DFE) tap adaptation, the method comprising:
receiving an input signal at a DFE of a receiver, wherein the input signal comprises a serial bit stream of encoded symbols;
sampling the input signal, using at least one data sampler, to provide data samples;
sampling the input, using at least one error samplers, to provide error samples;
aligning the data samples and the error samples to establish a plurality of pairs of data samples and error samples, wherein the data sample and error sample of each of the plurality of pairs of data samples and error samples are from locations in the serial bit stream of encoded symbols that are known to be uncorrelated with each other; and
adjusting a tap weight of one or more DFE taps based upon the plurality of pairs of data samples and error samples.
2. The method of claim 1 , wherein aligning the data samples and the error samples to establish a plurality of pairs of data samples and error samples, further comprises:
aligning the data samples and the error samples using one or more symbol boundaries to establish the plurality of pairs of data samples and error samples.
3. The method of claim 1 , wherein aligning the data samples and the error samples to establish a plurality of pairs of data samples and error samples, further comprises:
identifying di-bit correlation properties of a plurality of bits of the serial bit stream of encoded symbols; and
aligning the data samples and the error samples based upon the di-bit correlation properties to establish the plurality of pairs of data samples and error samples.
4. The method of claim 1 , wherein adjusting a tap weight of one or more DFE taps based upon the plurality of pairs of data samples and error samples, further comprises maintaining a correlation count for each of the one or more DFE taps.
5. The method of claim 4 , wherein adjusting a tap weight of one or more DFE taps based upon the plurality of pairs of data samples and error samples, further comprises:
increasing the tap weight of the one or more DFE taps if the correlation count indicates that the data samples and the error samples are correlated; and
decreasing the tap weight of the one or more DFE taps if the correlation count indicates that the data samples and the error samples are anti-correlated.
6. The method of claim 1 , wherein aligning the data samples and the error samples to establish a plurality of pairs of data samples and errors samples further comprises:
aligning the data sample and the error sample of each of the plurality of pairs of data samples and error samples to be from different encoded symbols of the serial bit stream of encoded symbols.
7. The method of claim 1 , wherein the encoded symbols are 8b/10b encoded symbols, and wherein aligning the data samples and the error samples to establish a plurality of pairs of data samples and errors samples further comprises aligning the data sample and the error sample of each of the plurality of pairs of data samples and error samples in different 8b/10b encoded symbols of the serial bit stream of encoded symbols.
8. The method of claim 1 , wherein the encoded symbols are 8b/10b encoded symbols comprising a 5b/6b (5-bit word to 6-bit symbol) portion and a 3b/4b (3-bit word to 4-bit symbol) portion, and wherein aligning the data samples and the error samples to establish a plurality of pairs of data samples and errors samples further comprises aligning the data sample of a pair of data samples and error samples in the 5b/6b portion of an 8b/10b encoded symbol of the serial bit stream of encoded symbols and aligning the error sample of the pair of data samples and error samples in the 3b/4b portion of the 8b/10b encoded symbol of the serial bit stream of encoded symbols.
9. The method of claim 1 , wherein the receiver is a Serializer/Deserializer (SerDes) receiver.
10. A system comprising:
a decision feedback equalizer (DFE) comprising one or more taps, the DFE configured to receive an input signal comprising a serial bit stream of encoded symbols, the DFE including at least one data sampler for sampling the input signal to provide data samples and at least one error sampler for sampling the input signal to provide error samples;
an alignment analyzer configured to align the data samples and the error samples and configured to establish a plurality of pairs of data samples and error samples, wherein the data sample and error sample of each of the plurality of pairs of data samples and error samples are from locations in the serial bit stream of encoded symbols that are known to be uncorrelated with each other; and
a correlation analyzer configured to adjust a tap weight of the one or more DFE taps based upon the plurality of pairs of data samples and error samples.
11. The system of claim 10 , wherein the alignment analyzer is further configured to:
align the data samples and the error sample using one or more symbol boundaries to establish the plurality of pairs of data samples and error samples.
12. The system of claim 10 , wherein the alignment analyzer is further configured to:
identify di-bit correlation properties of a plurality of bits of the serial bit stream of encoded symbols; and
align the data samples and the error samples based upon the di-bit correlation properties to establish the plurality of pairs of data samples and error samples.
13. The system of claim 10 , wherein the correlation analyzer comprises at least one correlation counter, the at least one correlation counter configured to maintain a correlation count for each of the one or more taps of the DFE, and wherein the tap weight of the one or more DFE taps is increased if the correlation count indicates that the data samples and the error samples are correlated and the tap weight of the one or more DFE taps is decreased if the correlation count indicates that the data samples and the error samples are anti-correlated.
14. The system of claim 10 , wherein the alignment analyzer is further configured to identify di-bit correlation properties of a plurality of bits of the serial bit stream of encoded symbols of the input signal and to align the data samples and error samples based upon the di-bit correlation properties to establish the plurality of pairs of data samples and error samples.
15. The system of claim 10 , wherein the alignment analyzer is further configured to align the data samples and error samples with a symbol boundary of the encoded symbols to establish the plurality of pairs of data samples and error samples.
16. The system of claim 10 , wherein the alignment analyzer is further configured to select the data sample and error sample of each of the plurality of pairs of data samples and error samples to be from different symbols of the serial bit stream of encoded symbols.
17. The system of claim 10 , wherein the encoded symbols are 8b/10b encoded symbols comprising a 5b/6b (5-bit word to 6-bit symbol) portion and a 3b/4b (3-bit word to 4-bit symbol) portion, the alignment analyzer is further configured to align the data samples and error samples with a 6-bit/4-bit symbol boundary to establish the plurality of pairs of data samples and error samples.
18. A system comprising:
a decision feedback equalizer (DFE) comprising one or more taps, the DFE configured to receive an input signal comprising a serial bit stream of 8b/10b encoded symbols,
the DFE including at least one data sampler configured to sample the input signal to provide data samples and at least one error sampler configured to sample the input signal to provide error samples;
an alignment analyzer configured to align the data samples and the error samples to establish a plurality of pairs of data samples and error samples, wherein the data sample and error sample of each of the plurality of pairs of data samples and error samples are from locations in the serial bit stream of encoded symbols that are known to be uncorrelated with each other;
a correlation analyzer configured to adjust a tap weight of the one or more DFE taps based upon the plurality of pairs of data samples and error samples; and
a deserializer coupled to the alignment analyzer and to the correlation analyzer, the deserializer configured to drop one or more bits of the input signal to align the data samples and the error samples to establish the plurality of pairs of data samples and error samples.
19. The system of claim 18 , wherein the encoded symbols are 8b/10b encoded symbols comprising a 5b/6b (5-bit word to 6-bit symbol) portion and a 3b/4b (3-bit word to 4-bit symbol) portion, and wherein the alignment analyzer includes a circuit configured to align the data samples and error samples with a 6-bit/4-bit symbol boundary to establish the plurality of pairs of data samples and error samples.