AD8190

Rev. 0 | Page 18 of 24

APPLICATION NOTES

Figure 31. Evaluation Board Layout of the TMDS Traces

The AD8190 is an HDMI/DVI switch featuring equalized

TMDS inputs and pre-emphasized TMDS outputs. It is in-

tended for use as a 2:1 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 AD8190 was designed to have an HDMI/DVI receiver

pinout at its input and a transmitter pinout at its output. This

makes the AD8190 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

AD8190 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, as shown in Figure 32.

One advantage of the AD8190 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 AD8190 provides up to 6 dB of

output pre-emphasis that boosts the output TMDS signals and

allows the AD8190 to precompensate when driving long PCB

traces or output cables. The net effect of the input equalization

and output pre-emphasis of the AD8190 is that the AD8190 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 AD8190 can be

found in the Typical Performance Characteristics section.

The AD8190 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 AD8190 on the

PCB requires a designer to place vias in the high speed signal

path, the AD8190 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 AD8190.

The programmable output terminations also improve signal

quality at the output of the AD8190. The PCB designer, there-

fore, has significantly improved flexibility in the placement and

routing of the output signal path with the AD8190 over other

solutions.

An example of high speed routing from an HDMI Standard

Revision 1.2a receive-compliant reference design is shown in

Figure 32. The light gray TMDS lines are routed on the top layer

of the PCB, the dark gray TMDS lines are routed on the bottom

layer, and the black dots are vias.

AD9880 (Rx)

AD8190

HDMI IN

HDMI IN

J4

Figure 32. Layout of the TMDS Traces for the AD8190 in an HDMI Standard

Revision 1.2a Receive-Compliant Reference Design