Re: CRT anode discharge



I had a similar experience in the mid 70's as a young design engineer. I had a multi-input ADC which was implemented with a single ADC, a S/H and a couple of multiplexers. The problem I had with dielectric absorption was with the single sample and hold capacitor where I had initially used a polycarbonate. The side effect of the dielectric absorption was that it caused a small cross-coupling from one channel to the next one that was to be converted due to charge being left on the hold capacitor. Ultimately the problem was resolved by utilizing a Teflon dielectric capacitor which had a very low dielectric absorption, and a price tag reflecting that.


Hi Bruce,
During a project as a young engineer in the early 70's I was tasked with the design
implementation of a unique multi channel ADC which required input sample-and-hold
blocks. Initially, for the storage caps I naively chose 330 pF ceramic caps that had, in
that application, a bad soak issue.(read: plainly obvious, like 1 to 3ish percent, when
you look on a scope, understand what you're seeing and how to fix it).
It took a bit of head scratching to figure out what was going on... not totally unlike
someone getting zapped by soak, its an effect I'll never forget..

As I recall, both Bob Pease and Al Williams have written of their soak experiences
and knowledge.

Dielectric soak isn't just for folks trying to pinch off that last .001% of THD. ;-)

Roger Marin, KJ7SGV

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