AD8191 Analog Devices, AD8191 Datasheet - Page 24

• Manufacturer Part Number: AD8191
• Description: 4:1 DVI/HDMI Switch with Equalization Preliminary Data Sheet (Rev. PrJ, 8/2006)
• Manufacturer: Analog Devices

AD8191
APPLICATION NOTES
The AD8191 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 1.2a
receive compliant.
PINOUT
The AD8191 was designed to have an HDMI/DVI receiver
pinout at its input and a transmitter pinout at its output. This
makes the AD8191 ideal for use in AVR-type applications
where a designer would route both the inputs and the outputs
directly to HDMI/DVI connectors. This type of layout is
illustrated in the schematic for the AD8191 evaluation board
(Figure 17) and in the layout of the evaluation board (Figure
18). When the AD8191 is used in receiver type applications, it is
necessary to change the ordering of the output pins on the PCB
to match up with the on-board receiver.
One advantage of the AD8191 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 17. In addition to
12 dB of input equalization, the AD8191 provides up to 6 dB of
output pre-emphasis that boosts the output TMDS signals and
allows the AD8191 to precompensate when driving long PCB
Figure 18. Evaluation Board Layout of the TMDS Traces
Figure 17. AD8191 Evaluation Board Schematic
Rev. PrJ | Page 24 of 29
traces or output cables. The net effect of the input equalization
and output pre-emphasis of the AD8191 is that the AD8191 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.
The AD8191 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 AD8191 on the
PCB requires a designer to place vias in the high speed signal
path, the AD8191 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
AD8191. The programmable output terminations also improve
signal quality at the output of the AD8191. The PCB designer,
therefore, has significantly improved flexibility in the placement
and routing of the output signal path with the AD8191 over
other solutions.
CABLE LENGTHS AND EQUALIZATION
The AD8191 offers two levels of programmable equalization
for the high speed inputs: 6 dB and 12 dB. The equalizer of
the AD8191 is optimized for video data rates of 1.65 Gbps. It
can equalize up to 20 meters of 24 AWG HDMI cable at data
rates corresponding to the video format, 1080p.
Preliminary Technical Data