Bias and random delay cancellation
View Patent ↗A system and method for digital communication wherein a host provides a host clock and a clockless device transmits to the host a bit stream synchronized according to the clock at a data rate that is an integer multiple of the clock rate. A training mechanism using training data detects time skew between host clock and bit stream, and a digital skew compensation mechanism compensates, substantially in real time, for the skew and for variations in the skew that may occur with the passage of time, in accordance with a vote among at least three samples of a bit of the bit stream, subsequent sampling being retarded or advanced if, respectively, an early or late sample is in disagreement with the vote. Preferably, the compensation value is selected from at least four possible compensation values, and can be stored in a memory to hasten subsequent restarts of the system.
1. A digital communication system comprising:
(a) a host, said host including:
(i) a clock operative to produce a clock signal having a clock rate;
(ii) a receiver operative to sample bits of a bit stream according to a sampling timing determined according to said clock signal;
(iii) a skew compensation mechanism operative to adjust said sampling timing;
(iv) a voting mechanism operative to detect a skew between said clock signal and said bit stream according to a vote among at least three samples of a bit of said bit stream, and to adjust, via said skew compensation mechanism, said sampling timing so as to compensate for said skew, and
(v) a training mechanism operative to detect a skew between said clock signal and a training bit stream, said training mechanism being further operative, via said skew compensation mechanism, to adjust said sampling timing so as to compensate for said skew, and
(b) a device operative to transmit said bit stream and said training bit stream to said host, said bit stream and said training bit stream being synchronized according to said clock signal supplied by said host, said device lacking a clock,
and wherein said skew compensation mechanism is operative to adjust, substantially in real time, said sampling timing so as to compensate for said skew of (iv) and said skew of (v).
2. The system of claim 1 , wherein said samples in said vote include at least one early sample, at least one intermediate sample and at least one late sample.
3. The system of claim 1 , wherein said skew compensation mechanism includes a digitally adjustable sampling control mechanism operative to adjust timing of sampling of a bit of said bit stream according to a digital value, said digital value being in accordance with said vote.
4. The system of claim 3 , wherein said host is operative to store said digital value in a memory, and to subsequently restore said digital value according to said memory.
5. The system of claim 3 , wherein said digitally adjustable sampling control mechanism is operative to adjust timing of sampling of a bit of said bit stream according to a digital value that can be selected from at least four possible digital values.
6. The system of claim 2 , wherein said compensation includes retarding sampling of a subsequent bit if at least one said early sample is in disagreement with said vote.
7. The system of claim 2 , wherein said compensation includes advancing sampling of a subsequent bit if at least one said late sample is in disagreement with said vote.
8. The system of claim 2 , wherein said compensation includes retarding sampling of a subsequent bit if at least one said early sample is in disagreement with said vote and wherein said compensation further includes advancing sampling of a subsequent bit if at least one said late sample is in disagreement with said vote.
9. The system of claim 1 , wherein said bit stream includes user data.
10. The system of claim 1 , wherein said bit stream has a bit rate twice said clock rate.
11. The system of claim 1 , wherein said bit stream has a bit rate quadruple said clock rate.
12. The system of claim 1 , wherein said bit stream has a bit rate eight times said clock rate.
13. The system of claim 1 , wherein said bit stream has a bit rate that is an integer multiple of said clock rate.
14. A digital communication system comprising a host, said host including:
(a) a clock operative to produce a clock signal having a clock rate;
(b) a receiver operative to sample bits of a bit stream according to a sampling timing determined according to said clock signal;
(c) a skew compensation mechanism operative to adjust said sampling timing;
(d) a voting mechanism operative to detect a skew between said clock signal and said bit stream according to a vote among at least three samples of a bit of said bit stream, and to adjust, via said skew compensation mechanism, said sampling timing so as to compensate for said skew, and
(e) a training mechanism operative to detect a skew between said clock signal and a training bit stream, said training mechanism being further operative, via said skew compensation mechanism, to adjust said sampling timing so as to compensate for said skew,
and wherein said skew compensation mechanism is operative to adjust, substantially in real time, said sampling timing so as to compensate for said skew of (d) and said skew of (e).
15. The system of claim 14 , wherein said samples in said vote include at least one early sample, at least one intermediate sample and at least one late sample.
16. The system of claim 14 , wherein said skew compensation mechanism includes a digitally adjustable sampling control mechanism operative to adjust timing of sampling of a bit of said bit stream according to a digital value, said digital value being in accordance with said vote.
17. The system of claim 16 , wherein said host is operative to store said digital value in a memory, and to subsequently restore said digital value according to said memory.
18. The system of claim 16 , wherein said digitally adjustable sampling control mechanism is operative to adjust timing of sampling of a bit of said bit stream according to a digital value that can be selected from at least four possible digital values.
19. The system of claim 15 , wherein said compensation includes retarding sampling of a subsequent bit if at least one said early sample is in disagreement with said vote.
20. The system of claim 15 , wherein said compensation includes advancing sampling of a subsequent bit if at least one said late sample is in disagreement with said vote.
21. The system of claim 15 , wherein said compensation includes retarding sampling of a subsequent bit if at least one said early sample is in disagreement with said vote and wherein said compensation further includes advancing sampling of a subsequent bit if at least one said late sample is in disagreement with said vote.
22. The system of claim 14 , wherein said bit stream includes user data.
23. The system of claim 14 , wherein said bit stream has a bit rate twice said clock rate.
24. The system of claim 14 , wherein said bit stream has a bit rate quadruple said clock rate.
25. The system of claim 14 , wherein said bit stream has a bit rate eight times said clock rate.
26. The system of claim 14 , wherein said bit stream has a bit rate that is an integer multiple of said clock rate.