TMDS (Transition Minimised Differential Signalling) is a nominally differential signalling specification used, for example, in DVI & HDMI.
Today though I was reading Brooks' Signal Integrity Issues, which defines differential signalling as a mode with two conductors, one carrying a signal and the other carrying an inverted copy of it - providing the return path - so that there is no return through ground.
Looking at the diagram of a TMDS tx/rx pair in the DVI spec (pg. 33) (copied below), it appears though that this condition is not met. The transmitter sinks or does not sink current on one or the other line. Due to configuration of the receiver there appears an equal and opposite voltage across each of the two termination resistors, but only one conductor at a time actually carries current, leaving the return path I presume to be the data[x]_gnd lines that are found on a typical DVI connector (signified by the third net in that schematic between the transmitter and receiver?).
Is this assessment correct or have I missed something about how it operates?
According to Brooks' definition, is Transition Minimised Differential Signalling actually differential?