Orthogonal differential vector signaling
Using a transformation based at least in part on a non-simple orthogonal or unitary matrix, data may be transmitted over a data bus in a manner that is resilient to one or more types of signal noise, that does not require a common reference at the transmission and acquisition points, and/or that has a pin-efficiency that is greater than 50% and may approach that of single-ended signaling. Such transformations may be implemented in hardware in an efficient manner. Hybrid transformers that apply such transformations to selected subsets of signals to be transmitted may be used to adapt to various signal set sizes and/or transmission environment properties including noise and physical space requirements of given transmission environments.
1. A method comprising:
receiving a set of N symbols of a codeword on a multi-wire bus, wherein N is an even integer;
generating a set of N−1 output signals, each output signal of the set of N−1 output signals generated using a voltage adder circuit to form a respective summation of the N symbols of the codeword, wherein each symbol in the respective summation has a sign applied by the voltage adder circuit determined by a corresponding element in a respective row of a set of N−1 rows of a non-simple orthogonal matrix, wherein each row of the set of N−1 rows is (i) mutually orthogonal and (ii) orthogonal to an all-one common mode row; and
generating a set of N−1 output bits based on the set of N−1 output signals.
2. The method of claim 1 , wherein the set of N symbols of the codeword is represented as analog signal levels on the multi-wire bus.
3. The method of claim 2 , wherein the respective summation is an analog summation of the analog signal levels.
4. The method of claim 3 , wherein the voltage adder circuit comprises analog adders and subtractors.
5. The method of claim 1 , wherein each output signal in the set of N−1 output signals has a value selected from a corresponding set of two values.
6. The method of claim 1 , wherein generating the set of N−1 output bits comprises slicing the set of N−1 output signals.
7. The method of claim 1 , wherein the non-simple orthogonal matrix is a Hadamard matrix.
8. The method of claim 7 , wherein the Hadamard matrix is a Sylvester-type Hadamard matrix.
9. The method of claim 1 , further comprising:
receiving a set of N−1 input bits, and responsively generating a set of N−1 input signals;
generating a second set of N symbols of a second codeword, the second set of N symbols based on a weighted summation of the set of N−1 rows of the non-simple orthogonal matrix, each row weighted with a corresponding input signal of the set of N−1 input signals; and
transmitting the second set of N symbols on the multi-wire bus.
10. The method of claim 9 , wherein the set of N−1 input bits correspond to the set of N−1 output bits.
11. An apparatus comprising:
a multi-wire bus configured to receive a set of N symbols of a codeword, wherein N is an even integer;
a voltage adder circuit configured to generate a set of N−1 output signals, each output signal of the set of N−1 output signals generated based on a respective summation of the N symbols of the codeword, wherein each symbol in the respective summation has a sign applied by the voltage adder circuit determined by a corresponding element in a respective row of a set of N−1 rows of a non-simple orthogonal matrix, wherein each row of the set of N−1 rows is (i) mutually orthogonal and (ii) orthogonal to an all-one common mode row; and
a detector configured to generate a set of N−1 output bits based on the set of N−1 output signals.
12. The apparatus of claim 11 , wherein the set of N symbols of the codeword are analog signal levels on the multi-wire bus.
13. The apparatus of claim 12 , wherein the voltage adder circuit is configured to perform the respective summation by performing an analog summation of the analog signal levels.
14. The apparatus of claim 13 , wherein the voltage adder circuit comprises analog adders and subtractors to perform the analog summation.
15. The apparatus of claim 11 , wherein each output signal in the set of N−1 output signals has a value selected from a corresponding set of two values.
16. The apparatus of claim 11 , wherein the detector is configured to generate the set of N−1 output bits by slicing the set of N−1 output signals.
17. The apparatus of claim 11 , wherein the non-simple orthogonal matrix is a Hadamard matrix.
18. The apparatus of claim 17 , wherein the Hadamard matrix is a Sylvester-type Hadamard matrix.
19. The apparatus of claim 11 , further comprising:
a balancer configured to receive a set of N−1 input bits, and to responsively generate a set of N−1 input signals;
an encoder configured to generate a second set of N symbols of a second codeword, the second set of N symbols based on a weighted summation of the set of N−1 rows of the non-simple orthogonal matrix, each row weighted with a corresponding input signal of the set of N−1 input signals; and
a plurality of line drivers configured to transmit the second set of N symbols on the multi-wire bus.
20. The apparatus of claim 19 , wherein the set of N−1 input bits correspond to the set of N−1 output bits.