> I always thought capacitors as simple bulk storage devices, use some big
ones to filter out the ripple on power supplies and bunches of lil ones on
chips for adding the last "umph" when they switch and draw more current.

> But ive seen and read stuff about using a mix of big and small for better
frequency response.  But can someone explain exactly what that means?  If
you have a circuit running at 20 MHz do you need to worry about a cap that
responds at 100MHz?  I just am not so clear on this (frequency response of a
cap).

> Sorry if this is too basic of a question.

Stop apologising already :-) How are you ment to learn if you don't ask
questions?


Quick comment as its (past) bed time here.

All capacitors are non ideal.
They have lead inductance and may have inductance internally due to
construction.
They have resisatnce in the way that they are made plus lead resistance
9usually unimportant).
They have leakage between "sides"

All this varies with type and size and ....

Large Aluminium "wet" electrolytics have the benefit of being compact per
capacitance but are quite non ideal in most ways. They have large internal
inductance (as they are spiral wound), finite internal resistance to signals
that gets worse with age, leakage across the electrolyte and insulating
oxide, and they degradde with temperature and time. But they are cheap
relatively.

All capacitor types have some non ideal feature or other. With some the main
bad point is price and/or size. eg Polysturene is superb but bulky and
expensive.

Ceramics are cheap but inaccurate (hard to set accuratel) and poor
temperature coefficient (depending on material), and have piezo effects and
can ring and overvoltage.

Tantalum caps are electrically superior to Al in most respects and are good
signal bypas caps BUT explode, burn, smell, smoke and generally have a good
time when you exceeed their ratings with a high energy voltage spike.

So it's "horses for courses".

Someone else can pick this up and talk about decoupling etc OR ask Google
knowing what you now do.

Good night


        RM




___________________________________________________________
If we have already accidentally created an unexpectedly lethal virus by
single
gene transfer, why should we believe that it might not happen again, once
or on numerous occasions in future, but in less controlled circumstances?

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body