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HPD Pins

DDC Channels

Configuring the TMDS341A as a 2:1 Switch

Layout Considerations

Connecting Cables Longer Than 5 m

TMDS Signal Path

TMDS341A

SLLS702 – MAY 2006

APPLICATION INFORMATION (continued)

The PRE pin provides 3-dB de-emphasis, allowing output signal pre-conditioning to offset interconnect losses

from the TMDS341A outputs to a TMDS receiver. PRE is recommended to be low to the circuit design of a

stand-alone switch box.

The input of the HPD_SINK is 5-V tolerant, allowing direct connection to 5-V signals. The HPD pin output

resistance is 35-

Ω typically. A 1-kΩ 10% resistor is recommended to be connected from an HPD pin at the

TMDS341A to the HPD pin of the HDMI connector.

The DDC channels are designed with a bi-directional pass gate, providing 5-V signal tolerance. The 5-V

can be eliminated.

The TMDS341A can be configured as a 2-to-1 switch by pulling the source selector pin (S1, S2, S3) of the

non-active port low and leaving the corresponding TMDS inputs, SCL, SDA, and HPD pins open.

The high-speed TMDS inputs are the most critical paths for the TMDS341A. There are several considerations to

minimize discontinuities on these transmission lines between the connectors and the device:

•

Maintain 100-

Ω differential transmission line impedance into and out of the TMDS341A

•

Keep an uninterrupted ground plane beneath the high-speed I/Os

•

Keep the ground-path vias to the device as close as possible to allow the shortest return current path

•

Layout of the TMDS differential inputs should be with the shortest stubs from the connectors

When using the TMDS341A with cables longer than 5 m, the impact to the TMDS signal path as well as the

DDC signal path must be considered.

The TMDS341A receiver equalization circuit provides the capability of compensating inter-symbol interference

(ISI) losses in a 5-m 28-AWG DVI cable. Typical cable measurements indicate that the TMDS341A can drive a

5-m 28-AWG HDMI cable and pass the eye mask at the output of a HDMI source (TP1) and a 10-m 28-AWG

HDMI cable and pass the eye mask at the input of a HDMI sink (TP2). Figure 34 through Figure 37 show the

eye mask measurement results.

Figure 34. Eye Diagram at Output 5-m 28-AWG Cable vs

Figure 35. Eye Diagram Recovered by TMDS341A vs TP1

TP1 Eye Mask

Eye Mask

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