[sdiy] Help, I'm Desperate! (Charge Injection with DG408)

Guy McCusker guy.mccusker at gmail.com
Tue Dec 4 10:38:47 CET 2018

> - Here is my main suggestion as to what it might be. It sounds like (we
> only have your description of the circuit to go on) you are generating
> the three-bit control word for the analogue switch from the outputs of
> several analogue comparators. How sure are you that the transition from
> one digital value to the next is clean, i.e. that all three bits change
> state at exactly the same time? If the three-bit word passes through any
> intermediate "runt" states on its way, the switch will briefly select a
> completely different input and potentially inject spikes of something
> else into the output. This is an issue in digital systems (search "race
> hazards") and is likely to be even worse if comparatively slow and
> imprecise analogue comparators are involved.

Ah, this is interesting. I am toying with something that involves
switching with a DG408 too, and had started wondering about using a
CMOS priority encoder (CD4532) to generate the three bit words from an
analog select signal. Might something like that help to get clean
switching signals here too?

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