On Thu, Jun 05, 2003 at 10:29:29AM +1000, Ian Wilson wrote: > about is minimising the AC impedance between the power nets over a suitably > broad range of frequencies and to an adequately low level - both > application dependent. Operating past resonance simply means the impedance > is inductive and rising with freq - so what, as long as it is low enough, > that is generally all you need to know.
yes - just as long as we are not getting too near the parallel resonance. A Q issue as you point out. > may have problems in production. I can imagine what the production team > would think about trimmable decoupling caps. :-) select on test decouplers I have yet to resort to fortunately :) > > 1nF of *high-Q* interplane capacitance! Not likely, even if the parallel sorry if I was unclear. I did not mean to suggest the board planes were this good. 100p ~ 1N NPO may win in a brief band somewhere between 100M and 1G. The plane cap helps a bit there and above. 100n or 10n is more useful at lower frequencies, - a NPO does not eliminate them - but sometimes can help the 10n/100n's a little further away to be useful. > that much, when one is looking like a high impedance the other is becoming > a low impedance - a high impedance in parallel with a low is a low.. Take > the published cap models and do some SPICE sims - it is easy to see the > results. Better still use real caps and a spec-an/tracking generator or > VNA. I think the VNA is the tool of choice for designing this stuff. A spec an can tell you how much noise you have got - but its tough to be analytical when the noise injection model from a FPGA say is so lacking. john * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 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] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
