Methods and systems for high bandwidth communications interface
Systems and methods are described for transmitting data over physical channels to provide a high bandwidth, low latency interface between a transmitting device and a receiving device operating at high speed with low power utilization. Communication is performed using group signaling over sets of four wires using a vector signaling code, where each wire of a set carries a low-swing signal that may take on one of four signal values. Topologies and designs of wire sets are disclosed with preferred characteristics for group signaling communications.
1. A method comprising:
receiving signals via wires of a plurality of wires to obtain signal values, the signal values representing symbols of a codeword of a balanced vector signaling code;
detecting a plurality of detected elements by a method comprising for each respective detected element:
obtaining a respective first sum of a first selected pair of signal values;
obtaining a respective second sum of a second pair of signal values;
comparing the respective first sum and the respective second sum to obtain the respective detected element; and
introducing a correction signal derived from a previous detected element into one or more of the respective first sum, the respective second sum, and an offset of the comparison of the respective first and second sums; and
outputting received data derived from the plurality of detected elements.
2. The method of claim 1 , wherein the detected elements represent bits of received data.
3. The method of claim 1 , wherein the symbols of the codeword of the balanced vector signaling code have values selected from the set [±1, ±⅓].
4. The method of claim 3 , wherein the codeword is a permutation of ±[±1, −⅓, −⅓, −⅓].
5. The method of claim 1 , wherein an orthogonal matrix is used to determine each of the first and second pairs of selected wires for each detected element of the plurality of detected elements.
6. The method of claim 5 , wherein rows of the orthogonal matrix determine the first and second pairs of selected wires for each detected element of the plurality of detected elements.
7. The method of claim 5 , wherein the orthogonal matrix is represented as:
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+
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1
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1
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.
8. The method of claim 1 , wherein three detected elements are used in deriving the received data.
9. The method of claim 1 , wherein the detected elements are analog signals formed by a linear combination of the symbols of the codeword.
10. The method of claim 9 , further comprising slicing the analog signals to obtain a set of output bits.
11. A system comprising:
a line receiver configured to receive signals from a plurality of wires, the received signals representing symbols of a codeword of a balanced vector signaling code;
a plurality of mode detectors configured to generate a plurality of detected modes, each respective mode detector configured to:
compare a respective first sum of received signals from a first pair of selected wires and a respective second sum of received signals from a second pair of selected wires to produce a respective detected mode; and
derive receive output data from the plurality of detected modes; and
a decision-feedback equalization circuit configured to introduce a correction signal derived from a previous detected element into one or more of the respective first sum, the respective second sum, and an offset of the comparison of the respective first and second sums.
12. The system of claim 11 , wherein the detected elements represent bits of the receive output data.
13. The system of claim 11 , wherein the symbols of the codeword of the balanced vector signaling code have values selected from the set [±1, +⅓].
14. The system of claim 13 , wherein e codeword is a permutation of ±[1, −⅓, −⅓, −⅓].
15. The system of claim 11 , wherein an orthogonal matrix is used to determine the selected first and second pair of wires for each detected element of the plurality of detected elements.
16. The system of claim 15 , wherein rows of the orthogonal matrix determine the selection of the first and second pairs of selected wires for each detected element of the plurality of detected elements.
17. The system of claim 15 , wherein the orthogonal matrix is represented as:
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4
=
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+
1
+
1
+
1
+
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+
1
-
1
+
1
-
1
+
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+
1
-
1
-
1
+
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-
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]
.
18. The system of claim 11 , wherein the plurality of mode detectors comprises three mode detectors configured to detect three detected elements for use in deriving the receive output data.
19. The system of claim 11 , wherein the detected elements are analog signals formed by a linear combination of the symbols of the codeword.
20. The system of claim 19 , further comprising comparators configured to slice the analog signals to obtain a set of output bits representing the receive output data.