Datasheet

AD8197B
Rev. 0 | Page 23 of 28
APPLICATION INFORMATION
0
7015-030
Figure 31. Layout of the TMDS Traces on the AD8197B Evaluation Board (Only Top Signal Routing Layer is Shown)
The AD8197B is an HDMI/DVI switch, featuring equalized
TMDS inputs and pre-emphasized TMDS outputs. It is in-
tended for use as a 4:1 switch in systems with long cable runs
on both the input and/or the output, and is fully HDMI 1.3
receive-compliant.
PINOUT
The AD8197B is designed to have an HDMI/DVI receiver
pinout at its input and a transmitter pinout at its output. This
makes the AD8197B ideal for use in AVR-type applications
where a designer routes both the inputs and the outputs directly
to HDMI/DVI connectors, as shown in
Figure 31. When the
AD8197B is used in receiver type applications, it is necessary to
change the order of the output pins on the PCB to align with the
on-board receiver.
One advantage of the AD8197B in an AVR-type application
is that all of the high speed signals can be routed on one side
(the topside) of the board, as shown in
Figure 31. In addition to
12 dB of input equalization, the AD8197B provides up to 6 dB
of output pre-emphasis that boosts the output TMDS signals
and allows the AD8197B to precompensate when driving long
PCB traces or output cables. The net effect of the input equali-
zation and output pre-emphasis of the AD8197B is that the
AD8197B can compensate for the signal degradation of both
input and output cables; it acts to reopen a closed input data eye
and transmit a full swing HDMI signal to an end receiver. More
information on the specific performance metrics of the AD8197B
can be found in the
Typical Performance Characteristics
section.
The AD8197B also provides a distinct advantage in receive-type
applications because it is a fully buffered HDMI/DVI switch.
Although inverting the output pin order of the AD8197B on the
PCB requires a designer to place vias in the high speed signal
path, the AD8197B fully buffers and electrically decouples the
outputs from the inputs. Therefore, the effects of the vias placed
on the output signal lines are not seen at the input of the AD8197B.
The programmable output terminations also improve signal
quality at the output of the AD8197B. The PCB designer, there-
fore, has significantly improved flexibility in the placement and
routing of the output signal path with the AD8197B over other
solutions.
CABLE LENGTHS AND EQUALIZATION
The AD8197B offers two levels of programmable equalization
for the high speed inputs: 6 dB and 12 dB. The equalizer of
the AD8197B supports video data rates of up to 2.25 Gbps, and
as shown in
Figure 14, it can equalize more than 20 meters of
24 AWG HDMI cable at 2.25 Gbps, which corresponds to the video
format 1080p with deep color.