Signaling) differential pair is shown in 'Conceptual Schematic for one TMDS
differential pair' Figure. (See attached file: Conceptual schematic for one
TMDS differential pair.jpg)TMDS technology (transition minimized
differential signaling technology) uses current drive to develop the low
voltage differential signal at the Sink side of the DC-coupled transmission
line. The link reference voltage AVcc sets the high voltage level of the
differential signal, while the low voltage level is determined by the
current source of the HDMI Source and the termination resistance at the
Sink. The termination resistance (RT) and the characteristic impedance of
the cable (Z0) must be matched.
A single-ended differential signal, representing either the positive or
negative terminal of a differential pair, is illustrated in 'Single-ended
differential signal' Figure. The nominal high-level voltage of the signal
is AVcc and the nominal low-level voltage of the signal is (AVcc - Vswing).
Since the swing is differential on the pair, the net signal on the pair has
a swing twice that of the single-ended signal, or 2 Vswing. The
differential signal, as shown in 'Differential signal' Figure, (See
attached file: Differential signal.jpg) swings between positive Vswing and
negative Vswing.
The signal test points for a TMDS link (Transition Minimized Differential
Signaling Link) are shown in 'TMDS Link Test Points' Figure. (See attached
file: TMDS Link Test Points.jpg) TP1 is used for testing of HDMI Sources
and Transmitter components. TP2 is used for testing of HDMI Sinks and
Receiver components. TP1 and TP2 together are also used for testing of
cables.
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