Since mounting it on the board actually yields a lower SRF than is
quoted in the data sheets, having it somewhat higher turns out just
about right. For impedance matching, you don't want to be anywhere near
the SRF. Since those values are typically much less than
decoupling/bypassing values, it generally isn't a problem if you use the
same sizes (0603 ~1GHz, 0402 ~2GHz+)
> (Note: In the digital world, the rule is to use as big a decoupling
> capacitor as possible (for a given package inductance). The reason being, of
> course, is that in digital design the purpose of a 'decoupling capacitor' is
> to supply transient current to a devices when it switches. In other words,
> the decoupling capacitor is acting as a charge storage device, and
> the bigger the capacitor the better. It's interesting that while we both
> refer to those capacitors as "decoupling capacitors", they are used for
> very different reasons.)
I remember there being a distinction drawn between "bypassing" and
"decoupling" functions, but they seem almost to be the same thing.
Really we are accomplishing the same thing. While a decoupling cap
supplies the surge current it is lowering the supply impedance (V/I).
When/if it(they) runs out the available current drops, increasing the
impedance.
Seems many times digital and analog people are talking about the same
thing, but the terminologies get in the way. Examples:
D/A Convertor :)
rise time~=bandwidth, f.max
impedance matching~=attenuator
filter~=impedance matching
noise~=carrier
data~=noise
-- --------------------------------------------------------------- Mark Randol, RF Systems Engineer | Motorola SPS, Inc. (602)413-8052 Voice | M/S EL379 (602)413-4150 FAX | 2100 E. Elliot Road [email protected] | Tempe, AZ 85284 ---------------------------------------------------------------**** To unsubscribe from si-list: send e-mail to [email protected]. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu/si-list ****