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From: "John Jardine"
Subject: Re: CMMR op amp outside voltage rails ?
Date: Thu, 5 Dec 2002 19:14:53 -0000
NNTP-Posting-Date: 5 Dec 2002 19:02:41 GMT
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Gibbo wrote in message
> I have simulated and breadboarded (they almost agreed !) an amplifier that
> need with the following specs:-
> Differential voltage input of -60mV to +60mV
> This could be sitting on an offset between -5 volts to +50 volts
> Available power supply is a single rail 5 or 6v (not yet decided)
> Gain of 50 and 500 (switchable)
> Bandwidth DC to 1KHz
> Gain accurancy better than 1%.
> Offset accuracy less than 0.05 volts on the output.
> Temperature/time drift of offset is not such an issue as the micro
> calibrates for this. Though of course it would be nice to remove this
> My solution uses 3 op amps. One of them to remove the offset on the input.
> as the differential amp, and one for the gain There has to be a less
> complicated way.
> I bet there's a single package that will do it all ?
> Ideas ?
Sorry-- I've no ideas, but I was just for interest wondering how you've
arranged that 1st op-amp?.
(As I read it). If you've got a 0V and +5V supply for the 3 op-amps they can
be asked to work at bottom end with (say) a -5V signal and a -4.99V signal.
How are you removing the negative common mode offset voltage if the amps are
run from 0-5V?. (I'm assuming all the voltages are not isolated from each
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