HDMI Layout Notes for EOMA68 Cards by Richard Wilbur

Goals

The portion of the HDMI transmission path contained on the PCB has several goals: 1. Support all operating modes of the HDMI v1.4 interface of which the A20 chip is capable (clock up to 340MHz, data up to 3.4GHz). 2. Match the characteristic impedance of the rest of the HDMI transmission path (connectors, cable, and receiver) to minimize reflections and deliver a recoverable/decodeable signal to the receiver. [low distortion, sufficient amplitude] 3. Minimize radiated Electro-Magnetic Interference which could adversely effect other circuits on the EOMA68-A20 or in its surroundings, or exceed regulatory limits of concerned agencies: FCC, CSA, etc. 4. Minimize sensitivity to EMI from other circuits on the EOMA68-A20 and its surroundings.

Of these goals careful layout realizing a microstrip geometry helps with minimizing EMI radiation and sensitivity, while impedance matching both minimizes signal reflections which distort the transmitted signal and delivers the signal energy to the intended receiver.