At 07:36 PM 6/11/02 -0400, Sean H. Breheny wrote:
>Hi all,
>
>Perhaps I'm not understanding something here, but how does the cap help
>with the leakage current? Isn't their always leakage current on the pin,
>regardless of whether you are sampling or not?

Leakage current is not the primary error source here.  The S/H capacitor on
the input of the a/d convertor presents a sudden 50 pF load to the input -
the droop that is caused while that cap charges is the error source.  Try
it sometime - write some code that reads the voltage on an analog
pin.  Apply some arbitrary voltage to an a/d input through a 10K resistor
and look at voltage on the pin with a scope.  Now change the resistor to
100K and look at it again.  Now add a 1 uF cap between the pin and ground
and look once more.

dwayne

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Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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