[sdiy] Capacitor types - which when?

[James Patchell]

Well, as I recall, there are two major ones.  One is that the capacitance 
is voltage dependent.  That is, as the voltage across the capacitor varies, 
so does the capacitance.  Another is the "memory" that the dielectric 
has.  If you charge the capacitor up, and then discharge it, it will tend 
to want to go back to the voltage it was just at.  A good demonstration of 
this is a 16 bit Data Acq. system I was called in on to fix.  They were 
only getting about 8 bit repeatability on it.  I looked at the circuit, and 
they had put an RC filter in the path to limit the bandwidth.  The system 
should have worked, but didn't.  When I looked inside the box, I noticed 
that they were using a Ceramic Cap, and told them that was their 
problem.  The engineer that designed it said BS, but, when I put a 
polystyrene cap in there, sure enough, 16 bit repeatability.

At 12:50 PM 5/16/2004 -0500, TIm Daugard wrote:
> > Ceramics have high dielectric figures (so the cap can be made small),
> > but at the cost of also being very nonlinear. That is why they should be
> > avoided in the audio path. But sometimes they are whats responsible for
>
>What are the ceramic non-linearities?
>
>Tim Daugard

         -Jim
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