IT66121FN View Datasheet(PDF) - ITE Tech. INC.

Part Name

Description

Manufacturer

IT66121FN

Low Power Transmitter with HDMI1.4 3D

ITE Tech. INC. 

IT66121FN

System Design Consideration

As a high-performance receiver/transmitter, ITE’s RX/TX is capable of receiving/transmitting those

signals that are attenuated and degraded by the HDMI cables. These signals are usually very small in

amplitudes in addition to the distortion that the cable inflicts on them. The analog front-end of ITE’s

RX/TX is designed to combat environment noises as well as interference to some degree. However, to

get the optimum performance the system designers should follow the guideline below when designing

the application circuits and PCB layout.

HDMI Differential Signal

The characteristic impedance of all differential PCB traces (RX2P/M, RX1P/M, RX0P/M, and

RXCP/M) should be kept 100_ all the way from the HDMI connector to ITE’s RX/TX. This is very

crucial to the system performance at high speeds. When routing these 4 differential transmission

lines (8 single-ended lines in total), the following guidelines should be followed:

1. The signals traces should be on the outside layers (e.g. TOP layer) while beneath it there

should be a continuous ground plane in order to maintain the called micro-strip structure,

giving stable and well-defined characteristic impedances.

2. Cornering, through holes, crossing and any irregular signal routing should be avoided so as

to prevent from disrupting the EM field and creating discontinuity in characteristic impedance.

3. ITE’s RX/TX should be placed as close to the HDMI connector as possible. Since the TMDS

signal pins of ITE’s RX/TX perfectly match the order of the connector pins, it is very

convenient to route the signal directly into the chip, without through holes or angling.

4. Carefully choose the width and spacing of the differential transmission lines as their

characteristic impedance depends on various parameters of the PCB: trace width, trace

spacing, copper thickness, dielectric constant, dielectric thickness, etc. Careful 3D EM

simulation is the best way to derive a correct dimension that enables nominal 100_

differential impedance. Please contact us directly for technical support of this issue.

5. The sensitive HDMI differential signals should be taken when routing. To reduce the

differential unbalanced effect, it is recommended to separate at least 3 times the dielectric

thickness between the signal layer and the reference layer to any other adjacent signal or

GND plane to reduce noise inference and jitter. (or 25 mils is enough space in almost PCB

stack)

ESD Consideration

Special care should be taken when adding discrete ESD devices to all differential PCB traces

(RX2P/M, RX1P/M, RX0P/M, and RXCP/M). ITE’s RX/TX is designed to provide ESD protection

for up to 2kV at these pins. Adding discrete ESD diodes could enhance the ESD capability, but at

the same time will inevitably add capacitive loads, therefore degrade the electrical performance at

www.ite.com.tw

Nov-2011 Rev:0.99 36/39

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