Multi-Differential Physical Signaling
Publication Date: 2004-Jan-27
The IP.com Prior Art Database
A method of differential signaling that incorporates two additional states to encode more information that would otherwise be communicated. In an embodiment, two states ([11,00] and [00,11]) are added to neighboring differential pairs to provide a total of six possible states.
1. Descriptive Title
Multi-Differential physical signaling
Traditional differential signaling improves signal quality, EMI, noise immunity and system noise over single ended, but requires more signal pins. [Debate about ground pin savings still generally show at least a few more pins for differential]. Electronic package IO pin count is often a critical, and over-subscribed resource, so a signaling technique that uses fewer pins but preserves differential benefits would be of great value.
A signaling method that has differential properties but has more logical states would allow fewer pins for a given bus width. This solution adds logical states to a collection of differential signals. In any differential pair there are two logical states 0 and 1, but for the following discussion they will be shown as two digits each to represent the physical state of the lines. So the two logical states of a differential pair are 10 and 01. In a differential pair 11 and 00 are illegal states, because the nature of differential is for one line to be the logical complement of the other, or to characterize it another way, to always have the same average value between the two signals. In a preferred implementation of this invention, two differential signal pairs are used. Each pair retains the two logical states, giving a total of 4 logical combinations [01 01], [01 10], [10 01], [10 10]. In addition, two more states are added: [11 00] and [00 11]. These are chosen because across the four signals they maintain an average value the same as the original four states.
How useful is this? To a first order it could be immediately useful based on any bandwidth or capacity increase of a given number of bits, but to save pins it must actually eliminate the need for a bit in a signal path. The point at which a single bit is saved can be seen in the comparative table:
Traditional Invention Signals Pairs States Bits States Bits 4 2 4 2 6 2.5 8 4 16 4 36 5.125 14 7 128 7 432 8.69... 16 8 256 8 1,296 10.27... 26 13 8,192 13 93,312 16+ 32 16 65,536 16 1,679,616 21+
[Note that in cases of odd numbers of pairs, one pair is operating as a traditional differential pair.]
From the table, it is seen that a 7 pair bus of the claimed invention replaces a traditional 8 bit bus and 13 pairs of the claimed invention replaces a tradition...