ADV3003

Rev. 0 | Page 12 of 16

APPLICATION NOTES

The ADV3003 is a TMDS buffer featuring equalized inputs

and pre-emphasized outputs. It is intended for use as a buffer

in HDMI/DVI systems with long input cable runs, and is fully

HDMI 1.3 receive-compliant.

PINOUT

The ADV3003 is designed to have an HDMI/DVI receiver

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

makes the ADV3003 ideal for use in advanced TV front-panel

connectors and AVR-type applications where a designer routes

both the inputs and the outputs directly to HDMI/DVI connec-

tors—all of the high speed signals can be routed on one side of

the board.

The ADV3003 provides 12 dB of input equalization, so it can

compensate for the signal degradation of long input cables.

In addition, the ADV3003 can also provide up to 6 dB of

pre-emphasis that boosts the output TMDS signals and allows

the ADV3003 to precompensate when driving long PCB traces

or high loss output cables. The net effect of the input equalization

and output pre-emphasis is that the ADV3003 can compensate

for signal degradation of both the input and output cables; it

acts to reopen a closed input data eye and transmit a full-swing

HDMI signal to an end receiver.

CABLE LENGTHS AND EQUALIZATION

The 12 dB equalizer of the ADV3003 is optimized for video

data rates of 2.25 Gbps and can equalize more than 20 meters

of 24 AWG HDMI cable at the input at 2.25 Gbps, the data rate

corresponding to the video format 1080p with 12-bit deep color.

The length of cable that can be used in a typical HDMI/DVI

application depends on a large number of factors including

•

Cable quality: The quality of the cable in terms of

conductor wire gauge and shielding. Thicker conductors

have lower signal degradation per unit length.

•

Data rate: The data rate being sent over the cable. The signal

degradation over HDMI cables increases with data rate.

•

Edge rates: The edge rates of the source. Slower input edges

result in more significant data eye closure at the

end of a cable.

•

Receiver sensitivity: The sensitivity of the terminating

receiver.

Because of these considerations, specific cable types and lengths

are not recommended for use with this equalizer. The ADV3003

equalizer does not degrade signal integrity, even for short input

cables.

PRE-EMPHASIS

The pre-emphasis of the ADV3003 acts to boost the initial

voltage swing of the output signals. Pre-emphasis provides a

distinct advantage in systems where the ADV3003 is driving

either high loss cables or long PCB traces, because the added

boost helps to ensure that the data eye at the far end of the

output cables or PCB traces meets the HDMI receive mask. The

use of pre-emphasis in a system is highly application specific.

PCB LAYOUT GUIDELINES

The ADV3003 is a 4-channel TMDS buffer, targeted for use in

HDMI and DVI video applications. Although the HDMI/DVI

link consists of four differential, high speed channels and four

single-ended, low speed auxiliary control signals, the ADV3003

buffers only the high speed signals.

The high speed signals carry the audiovisual (AV) data, which

is encoded by a technique called TMDS. For HDMI, the TMDS

data is further encrypted in accordance with the high bandwidth

digital content protection (HDCP) standard.

The TMDS signals are differential, unidirectional, and high

speed (up to 2.25 Gbps). The channels that carry the video data

must have a controlled impedance, be terminated at the receiver,

and be capable of operating up to at least 2.25 Gbps. It is especially

important to note that the PCB traces that carry the TMDS

signals should be designed with a controlled differential

impedance of 100 Ω. The ADV3003 provides single-ended

50 Ω terminations on chip for both its inputs and outputs.

Transmitter termination is not fully specified by the HDMI

standard, but its inclusion in the ADV3003 improves the

overall system signal integrity.

TMDS Signals

In the HDMI/DVI standard, four differential pairs carry the

TMDS signals. In DVI, three of these pairs are dedicated to

carrying RGB video and sync data. For HDMI, audio data is

also interleaved with the video data; the DVI standard does

not incorporate audio information. The fourth high speed

differential pair is used for the AV data-word clock, which

runs at one-tenth the speed of the video data channels.

The four high speed channels of the ADV3003 are identical.

No concession was made to lower the bandwidth of the fourth

channel for the pixel clock, so any channel can be used for any

TMDS signal; the user chooses which signal is routed over

which channel. In addition, the TMDS channels are symmetric;

therefore, the p and n of a given differential pair are inter-

changeable, provided the inversion is consistent across all

inputs and outputs of the ADV3003.