Chuck,
> > > The "steps" mentioned above have nothing to do with intrinsic
> > > properties of sensor chips and I doubt that anyone tries to
> > > size an A/D's lsb to some rms noise level
>
> > But that is EXACTLY how the A/D is sized in analog to digital systems.
It
> > isn't sized less, then you aren't getting all the data that is
available,
> > and if you size it more, then you simply throw the bits away as they are
> > noise.
> au contraire: the Shannon waveform sampling theorem would be that
> criterion, and that says the steps must be smaller by a factor of about 3
or
> more.
Actually, it's Nyquist, and it's 2 to 1. That is simply part of basis
sampling theory, and is inherent in any discussion of sampling, scanner
design included. Your comment said that the "steps" (of the A/D) had
nothing to do with the intrinsic properties of the CCD and that is simply
NOT true, which was my point, and the A/D IS in fact sized to the noise,
and that sizing is 2:1 typically.
> The A/D is scaled to keep the min to max signal
> range between just a few bits and below full house
I'm not sure what you mean by "The A/D is scaled..." because it is not.
The analog front end simply "matches" the output voltage range of the CCD
with the input voltage range of the A/D, which is not scaling the A/D at
all. It IS "scaling" the voltage TO the A/D.
> The size of the lsb is just not relevant nor is it significant (as
> for frame-to-frame waveform analysis/synthesis) in these scanner systems.
The size of the LSB IS in fact relevant, and IS a property of the noise,
and again, the choice of number of bits used in the A/D matched to the
noise (by a factor of two, but it's still matched to the noise). If you
have more bits, fine, but you can't have less, or you lose good data.
Regards,
Austin
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