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From: "Ian Buckner"
Subject: Re: Op-amp virtual earth not 0V
Date: Tue, 17 Sep 2002 14:35:02 +0100
Organization: Agilent Technologies
NNTP-Posting-Date: Tue, 17 Sep 2002 13:35:05 +0000 (UTC)
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"Nghia" wrote in message
> Hi all,
> I've just done an experiment with an unknown op-amp where we put in
> triangle wave (1 volt) at 100Hz into an inverting voltage gain
> gain of -10. The op-amp saturates at +-15V.
> Now when observing the virtual earth point I noticed that its not
> but a square wave of very low amplitude, also at 100Hz. Can't
> how much was zoomed in so can't remember the exact value.
> I've searched everywhere on the web and haven't found anything that
> could help me explained this. Why isn't it zero volts?
Amplifiers have finite gain, so there has to be a signal at the input
sufficient to provide the output signal. The size will be the
of the output signal divided by the open loop amplifier gain.
You noted that the signal at the virtual earth input of the amplifier
a square wave, although the driving signal and output signal were
triangular. Why would that be?
(Hint: amplifiers have finite bandwidth)
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