Of course you have right David, I was thinking just to the first question,
resolution can't be improved only if the signal have the same amplitude
like reference. For 87x, unfortunately the +vref can't be +1V.
Vasile

On Fri, 12 Oct 2001, David Duffy wrote:

> >Olin Lathrop wrote:
> >
> > > > But then, is there a method to do an A/D on an input
> > > > signal of 0V to 1V on the 16F873 using Vrefs?
> > >
> > > Not if you want full range of the A/D without external parts.  To get the
> > > full A/D range from a 0 to 1V signal requires an external amplifier.
>
> Vasile wrote:
> >   There is a method Olin, without any external operational amplifier.
> >You need only to sum the input signal with a 2V dc. This is quite simple
> >if you have an AC input signal. However method depends on the source
> >impedance of the input signal.
>
> By this do you mean shift the original up closer to Vref? How does this
> increase resolution? The shifted signal is still 1V in amplitude. Maybe
> I've misunderstood what you mean. I can't see how shifting it makes a
> difference. Only a signal with same range as Vref gives full resolution.
> The 1V signal is half of the min Vref, so there's no other way to get the
> full A/D resolution without amplifying it. Am I missing something here?
> Regards...
>
> ___________________________________________
> David Duffy        Audio Visual Devices P/L
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