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From: John Popelish
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X-Mailer: Mozilla 4.7 [en] (Win98; U)
Subject: Re: generating calibration voltage
Date: Tue, 07 Jan 2003 16:40:09 GMT
NNTP-Posting-Date: Tue, 07 Jan 2003 11:40:09 EST
Tom Torfs wrote:
> Hello All,
> I would like to generate a +/- 500uV (or something of that order of
> magnitude, exact value doesn't matter as long as it's stable)
> calibration voltage, 30Hz square wave referred to a common reference
> (not connected to ground). As input I have an LVCMOS 30Hz 0..3V
> (referenced to ground) square wave signal (I can provide the opposite
> phase as well if that would be useful). Supplies available are + and -
> 3V (from battery). The output will be looking into a very big input
> impedance (24 parallel 100 Gohm preamplifier inputs).
> The reference should see a large impedance (preferrably >= 10 Mohms)
> towards ground. I'm sure this must be feasible using some sort of
> opamp circuit. Maybe someone here has a nice suggestion for a general
> approach to this type of circuit from past experience?
> Thanks for your time.
How square must the square wave be? (What rise and fall times do you
require?) and how much capacitance to ground can you tolerate with
this floating output? What precision must the amplitude hold to? How
flat must the wave be (can there be any ringing on the flat portions
of the wave? There is no such thing as a mathematically perfect
square wave, so any implementation will deal with the imperfections
you can tolerate.
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