System and method for drift compensation in data communications
A method and system are provided for drift compensation, providing a live data approach to sampler offset calibration, such as for voltage and/or temperature (VT) drift. A serializer/deserializer (SerDes) system includes a SerDes receiver and receiver logic, the receiver logic including a forward error correction (FEC) module. A drift compensation device, or drift compensation engine, receives live error corrections from the FEC module based on FEC operations performed on live traffic passing through the SerDes receiver. A drift compensation command is provided to a data sampler in the SerDes receiver, to adjust a sampling voltage of the data sampler. When the system includes a plurality of data samplers, the drift compensation device determines the data sampler with which an error correction is associated. The drift compensation command can be sent after a threshold criterion is satisfied, such as completion of a statistics collection period, or a threshold number of corrections.
1. A system for voltage or temperature drift compensation in a serializer/deserializer (SerDes), the system comprising:
a SerDes receiver including a data sampler;
receiver logic comprising a forward error correction (FEC) module in communication with the SerDes receiver; and
a drift compensation drift compensation engine (DCE) in communication with the FEC module and configured to receive live traffic error corrections from the FEC module, the DCE comprising at least one error bias counter (EBC) configured to accumulate the received live traffic error corrections, the DCE further configured to provide a drift compensation command to the data sampler, the drift compensation command being based on an error bias associated with the collected received live traffic error corrections,
the SerDes receiver configured to adjust a sampling voltage of the data sampler based on the provided drift compensation command.
2. The system of claim 1 wherein the at least one EBC comprises:
a hardware register configured to store a current error bias value; and
an add/subtract element configured to increment or decrement the stored current error bias value in response to the received live traffic error corrections from the FEC module.
3. The system of claim 2 wherein the hardware register accumulates error bias statistics associated with the received live traffic error corrections.
4. The system of claim 2 wherein the hardware register accumulates error bias statistics associated with the received live traffic error corrections over a finite statistics collection period and the DCE provides the drift compensation command to the data sampler at the end of the statistics collection period.
5. The system of claim 1 wherein the DCE receives one or more errors per FEC block from the FEC module.
6. The system of claim 1 wherein the DCE only receives the first error of each symbol in a FEC block.
7. The system of claim 1 wherein the error bias comprises a difference between a number of bits changed from 0 to 1 by the FEC module, and a number of bits changed from a 1 to 0 by the FEC module.
8. The system of claim 1 wherein the DCE resets the EBC at the end of a current statistics collection period, or at the beginning of a new statistics collection period.
9. The system of claim 1 wherein the DCE further comprises:
a threshold detector configured to identify whether a threshold criterion has been achieved,
the DCE providing the drift compensation command in response to the threshold criterion having been achieved.
10. The system of claim 9 wherein the threshold detector is configured to detect whether the accumulated statistics reach a threshold value.
11. The system of claim 9 wherein the threshold detector is configured to detect whether a statistics collection period has been completed.
12. The system of claim 11 wherein the statistics collection period is between about 1 millisecond and about 1 second.
13. The system of claim 9 wherein:
the at least one EBC comprises a plurality of EBCs,
the threshold detector comprises a plurality of threshold detectors equal in number to the plurality of EBCs, each threshold detector being paired with a unique one of the plurality of data samplers, and
wherein the DCE further comprises a configuration register storing a threshold criterion associated with the counter with which the threshold detector is paired.
14. The system of claim 9 wherein:
the at least one EBC comprises a plurality of EBCs,
the threshold detector comprises a single threshold detector, and
wherein the DCE further comprises a configuration register storing a plurality of threshold criteria, each threshold criterion being associated with the EBC with which the threshold detector is paired.
15. The system of claim 1 wherein:
the SerDes receiver comprises a plurality of data samplers; and
the at least one EBC comprises:
a plurality of EBCs equal in number to the plurality of data samplers, each EBC in the plurality of EBCs being paired with a unique one of the data samplers, each EBC in the plurality of EBCs being configured to calculate a live traffic error correction statistic associated with the data sampler with which the EBC is paired.
16. The system of claim 1 wherein:
the SerDes receiver comprises a plurality of data samplers; and
the at least one EBC comprises:
a single EBC configured to associate each error correction with a unique one of the data samplers of the plurality of data samplers.
17. The system of claim 1 wherein:
the SerDes receiver comprises a plurality of data samplers; and
the at least one EBC comprises:
a plurality of EBCs; and
an error discriminator configured to identify the data sampler uniquely responsible for each error correction.
18. The system of claim 1 wherein the FEC module is configured to output to the drift compensation engine, in parallel, a received pattern and a corrected output, the corrected output comprising the corrected pattern or a correction mask to be applied to the received pattern to generate the corrected pattern.
19. The system of claim 1 wherein the FEC module is configured to output, to the drift compensation engine, bit corrections that have occurred in the FEC module.
20. The system of claim 1 wherein the SerDes receiver comprises:
a local accumulator, associated with the data sampler, configured to increment or decrement a current digital sampling level based on the received drift compensation command; and
a digital/analog converter (DAC), in communication with the local accumulator and associated with the data sampler, configured to generate in analog form a current sampling voltage calibration value based on the digital sampling level.
21. The system of claim 20 wherein the local accumulator comprises:
a LA register configured to store a digital sampling level associated with the current sampling voltage; and
an add/subtract element configured to increment or decrement the stored digital sampling level in response to outputs from the drift compensation engine.
22. The system of claim 1 wherein:
the data sampler comprises first and second data samplers, and
the at least one EBC comprises:
a first EBC configured to calculate a first live traffic error bias associated with the first data sampler, and
a second EBC counter configured to calculate a second live traffic error bias associated with the second data sampler.
23. The system of claim 1 wherein:
the data sampler comprises:
an even plus sampler for sampling an even bit assuming a previous sample was a 1;
an even minus sampler for sampling an even bit assuming a previous sample was a 1;
an odd plus sampler for sampling an odd bit assuming a previous sample was a 0;
an odd minus sampler for sampling an odd bit assuming a previous sample was a 0; and
the DCE comprises:
a first EBC configured to calculate a first live traffic error bias associated with the even plus sampler;
a second EBC configured to calculate a second live traffic error bias associated with the even minus sampler;
a third EBC configured to calculate a third live traffic error bias associated with the odd plus sampler; and
a fourth EBC configured to calculate a fourth live traffic error bias associated with the odd minus sampler.
24. A method of voltage or temperature drift compensation for a serializer/deserializer (SerDes) receiver, the method comprising:
performing, at receiver logic comprising a forward error correction (FEC) module, forward error correction on live traffic passing through the SerDes receiver;
generating, at the FEC module, live traffic error corrections based on the FEC operations performed on the live traffic passing through the SerDes receiver;
generating, at a drift compensation engine, a drift compensation command for a data sampler in the SerDes receiver, the drift compensation command being generated based on collected statistics associated with the generated live traffic error corrections; and
adjusting a sampling voltage at the data sampler based on the received drift compensation command.
25. A processor-implemented method for voltage or temperature drift compensation for a serializer/deserializer (SerDes) receiver including a data sampler, the processor-implemented method comprising:
receiving, from a forward error correction (FEC) module, live traffic error corrections, the live traffic error corrections being collected based on FEC operations performed on live traffic passing through the SerDes receiver;
generating a drift compensation command based on statistics associated with the received live traffic error corrections; and
sending the drift compensation command to the SerDes receiver for adjusting a sampling voltage of the data sampler.
26. A device for enabling voltage or temperature drift compensation for a serializer/deserializer (SerDes) receiver including a plurality of data samplers, the device comprising:
an error discriminator configured to receive, from a forward error correction (FEC) module, live traffic error corrections, and to provide a discrimination output to identify the data sampler in the plurality of data samplers uniquely responsible for each error correction;
at least one error bias counter, in communication with the error discriminator, the at least one error bias counter configured to identify a data sampler with which an error correction is associated, based on the discrimination output; and
a threshold detector configured to identify whether a threshold criterion associated with the at least one counter has been achieved,
wherein the device provides a drift compensation command for one of the plurality of data samplers based on statistics associated with the live traffic error corrections and in response to the threshold criterion having been achieved.