> First, my experience regarding layout is minimal at best since I seem to
> exhaust all the wrong ways first. I once took a class in multilayer layout > and was told that the capacitance between the power/ground planes > themselves was sufficient for decoupling high frequencies and that adding > pacitors could cause tuned circuits and troublesome resonances. I'm > simply asking, any views on that theory? That may be true at very low frequencies like 74LSxx parts, but as the edge rate goes up the capacitance needs to be closer to the pin. Most manufacturers today say to put decoupling capacitors as close to the power pins as possible and they try to make a power and ground such that the cap can be attached to both pins. >>common in today's circuits. Also, 0.01 uF caps are less expensive and take >>up less space (0805 vs. 1206). Huh? Why would you use a 1206 0.1uf for anything unless you needed 50WVDC or more rating? Everything I have read on bypassing for digital says to use 0603 or smaller parts since they have lower inductance, and at the moment 0603 is the most cost effective. On a current design I have 0603 0.1uf, 0.01uf and smaller, 0805 1uf and 1210 10uf ceramic caps, besides the larger tantalums. The previous designers, who no longer work for us, used 1210 0.1uf for all the bypassing and they put them on the other side of the board far away from the power pins with really small traces so they'd be comletely useless. It really makes life suck now that we need to get RFI compliance testing done, especially when they routed digital across ground plane cuts and routed ADC power on traces that snake all over the board, and.......I'm going home for a beer. Robert D. LaMoreaux MTS Systems Corp. Powertrain Technology Division 4622 Runway Blvd. Ann Arbor, MI 48108 734-822-9696 Fax 734-973-1103 Main Desk 734-973-1111 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/[EMAIL PROTECTED] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
