AVR-Chat

On Tue, 19 Jun 2007 18:39:45 -0400
 "David VanHorn" <microbrix@gmail.com> wrote:
> > And Op-Amps have their own input "leakage".
> >
> 
> Indeed, but the chip processes that do good analog are
> different from
> the ones that do good microcontrollers.

No argument there. Point, however: suppose that an op-amp
has an input current (bias or otherwise) of 1na. Suppose
"designer" uses an affective DC source resistance of 1M
(not equal both inputs). If said buffer is unity-gain,
there will be an output offset of 1mv from just this source
(plus others not yet enumerated). With a Vref of 2.048V and
10bit ADC, this represents about 1/2 LSB, right out the
chute. Now, add Vos, ground loop, input offset currents,
etc, the designer has to pay very close attention to that
simple op-amp circuit in order to realize the available
accuracy of the ADC. 

Of course, "everyone" knows  this, right?

Jim
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