Analog Video PCB Layout

Question

What special considerations and/or constraints are typically applied when routing analog video signals on a PCB (e.g. VGA, NTSC, etc). I'm thinking try and keep them routed on a single layer (i.e. at most 2 vias), try and keep a ground plane under the tracks, and minimize the number of other (digital) signals that cross over those tracks, match the lengths of the R, G, B, and Syncs to within a couple hundred mils. What I'm really asking, is what kinds of formal constraints do people use in Electrical CAD tools when dealing with Analog video signals?

Answer 1

DRC checks for analog signals depends on impedance. VGA/NTSC ports are usually 75ohms and impedance of copper tracks can be made to match if necessary but only affects frequency range where prop delay of path length is significant part of rise time. controlled ground plane impedances are normally not done for Video signals as F is too low. But power supply noise is a concern and phase/pulse noise rejection in amplifiers. So adequate decoupling / regulation for analog circuits is important. Propagation delays depend on dielectric constant but generally Average Propagation Delay= 2 nS / ft so not critical for most Video signals.