5
\$\begingroup\$

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?

\$\endgroup\$
  • \$\begingroup\$ crossing tracks are not as bad as parallel tracks if they're perpendicular. Perpendicular tracks don't cause coupling. \$\endgroup\$ – stevenvh Feb 22 '12 at 16:37
  • \$\begingroup\$ Also look up impedance requirements on your signal types, and adjust your trace widths, spacings, and height from plane to meet these requirements. Then your chip to PCB to connector should be a clean transmission line. \$\endgroup\$ – billt Feb 22 '12 at 19:38
3
\$\begingroup\$

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.

\$\endgroup\$
  • \$\begingroup\$ what is "F" when you say F is too low? Frequency? \$\endgroup\$ – vicatcu Apr 9 '12 at 17:01
  • 1
    \$\begingroup\$ yes perhaps Studio quality video equipment pays careful attention to phase shift. Just avoid high current signals near the video and decouple or separate the analog V+ from digital Vcc and keep separate ground paths for current. Use ground planes to absorb stray noise. \$\endgroup\$ – Sunnyskyguy EE75 Apr 10 '12 at 1:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.