At 09:57 PM 8/13/2008, you wrote:
> > used a band gap reference which has a low enough impedance
>
>The current requirement for Vref is a lot higher than that for the
>A/D i/p. d/s says +/- 5uA at acquisition, +/- 150uA for conversion.
>A sagging Vref would arguably make more of a difference to the
>result than a high-Z i/p voltage

Indeed, which is why it is unfortunate that Microchip chose to share the
reference input pin with the programming clock pin on certain PICs.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



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