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From: email@example.com (carltons)
Subject: Re: OP Amp Output Resistance
User-Agent: NewsWatcher-X 2.2.3b2
NNTP-Posting-Date: Fri, 27 Sep 2002 19:24:43 GMT
Date: Fri, 27 Sep 2002 19:24:43 GMT
In article <3D938FE9.firstname.lastname@example.org>,
> Can it be assumed the output resistance is the same or roughly the same
> near the power supply rails as it would be near the center of the output
> voltage swing?
> It is the linearity of the open loop output resistance with DC output
> most want to know about. But there is some interest in how this changes with
> frequency of current demand as well. Thanks Glenn for the reference to
> sheets for the AD811 and AD712. But the Fig 8 on page 5 of the AD811 spec is
> closed loop output resistance. TPC 6 on page 4 of the AD712 spec does
not say if
> the output resistance is closed or open loop.
Why is the output impedance of an ompamp being questioned in this thread?
It's low (within reasonable freq's of course). If there is concern about
the actual impedance, then I can only assume that someone is pushing a
design to limits. Perhaps an opamp is not a suitable device in this
case. Consider this comment anyway, even if you don't agree with me.
Perhaps a buffer stage on the opamp's output would provide the solution.
BTW, loads of specs out there have no stated test conditions on them.
That stinks, but it is a fact of life that one has to deal with everyday.
Many engineers think that writing specs is a demeaning way of making a
living rather than a way of communication to his fellow engineers.
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