Come on, Dave, a CCD is a digital device, subject to aliasing. The
charges represent the signal at a particular instant of its average over
a particular interval. (My CCD digital camera can take time exposures.)
A CCD's content may not be quantized in amount, but it is quantized in
time. In a camera, where the charges pertain to individual pixels, the
result is also quantized in space.
"Digital" and "subject to aliasing" are two different things.
As I believe the term "digital" is usually meant, it implies a
two-state (on/off) storage representation. It's not just that the
signal amplitude is quantized, but that the quantization uses a
power-of-two representation and storage system of some sort.
In that sense, an audio CCD uses a digital clocking structure to move
the charge along, but uses a non-digital system for representing the
signal level (a linear number of electrons). Yes, it's quantized in
time, and the electron charges themselves are quantized... but I don't
think that either of these qualifies it as "digital".
"Analog" is a very fuzzy and imprecise term, and I think that a CCD
can reasonably be called an analog system.
Even audio cassette tape is quantized in both time and amplitude, at
the level of the individual magnetic domains in the oxide or metal
particles.
--
Dave Platt AE6EO
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