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From: email@example.com (Tom Torfs)
Subject: Re: generating calibration voltage
Date: 7 Jan 2003 23:41:55 -0800
NNTP-Posting-Date: 8 Jan 2003 07:41:55 GMT
> How square must the square wave be? (What rise and fall times do you
Rise/fall times can be upto a few ms. I'm only interested in the
amplitude. The reason I can't just use a DC signal is that there is a
highpass filter with fc=0.1Hz after that (and also a lowpass filter
> and how much capacitance to ground can you tolerate with
> this floating output?
Something like 10 pF would be ideal.
> What precision must the amplitude hold to?
Preferrably something on the order of magnitude of a few uV.
> How flat must the wave be (can there be any ringing on the flat portions
> of the wave?
I would think the lowpass filter will take care of that, but with such
high risetimes allowed I don't think there's any reason for it to
To the people suggesting a transformer: that's very nice, but I do not
have room for a 30Hz transformer. The footprint of the entire design
is limited to a few square cm... that's why I was hoping for some
suggestions of doing this with some sort of opamp circuit.
My alternative if a floating output turns out to be too difficult is
to briefly hook up the reference to ground during calibration using a
switch with low impedance when on and very high impedance when off. I
could also use a differential mux per channel, but rather avoid that
as that would add many components (24 channels).
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