Neil - On Mon, Oct 19, 2009 at 01:20:23PM -0700, Neil Hendin wrote: > If you look at the RF S-Parameters of the capacitor at frequencies > above the self resonance, they look inductive, not capacitive.
I'm not sure what the precise definition is for the S-Parameters of a two-terminal device, but the conclusion is accurate. > Good RF decoupling standard practice is to use a smaller cap > (e.g. 20pF in parallel with some larger ones such as 1000pF > _and_ 0.1uF or larger as needed) to get a good broad band > capacitive reactance across frequency). I have yet to see a 20pF or 1000pF cap with less parasitic inductance than a decent (e.g., X5R) 0402 cap up in the uF range. Say, in particular, TaiyoYuden JMK105BJ225MV-F 2.2uF 0402 6.3V X5R 0.1560 in 100's If you're going to occupy board area with a cap and its connection to the power nets, can anyone explain why I should choose anything other than the largest value available in that size and voltage? OK, I suppose if you're building cell phones and selling them by the hundreds of thousands, the nickel you could save by using a lower value would add up. But for me, the cost of assembly and documentation probably exceeds the cost of the component itself. - Larry _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
