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From: firstname.lastname@example.org (Bill Sloman)
Subject: Re: generating calibration voltage
Date: 8 Jan 2003 03:07:44 -0800
NNTP-Posting-Date: 8 Jan 2003 11:07:44 GMT
email@example.com (Tom Torfs) wrote in message news:...
> Hello John,
> > How square must the square wave be? (What rise and fall times do you
> > require?)
> 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
> with fc=70Hz).
> > 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.
Hmm. 500uV isn't a lot of volts. An RM4 core fits into a 1cm cube,
more or less, and 500uV for 167mS is 8.33 microvolt/seconds, which
doesn't sound like all that much. You could get a couple of hundred
turns of 0.1mm diameter wire onto an RM4 former.
I haven't got my RM transformer design data at work, but I think that
you might be able to generate your signal without saturating an RM4
I'll have think about it tonight - if Tony Williams doesn't trump me
by winding one over his lunch-time ...
For the rest of the circuit, Vishay's MPM SOT-23 100:1 dividers come
to mind (Farnell order code 309-8552 and $6,77 in small quantities).
Bill Sloman, Nijmegen
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