Reading your panasonic ref Chuck, the claim to lower noise seems to be based
on two things:
1) the larger fill factor (% of utilised area for photo sensor)
2) the lower voltage on photo diode.
I believe the oly Kodak ccd sensors, in fact have a higher fill factor still,
both because they are CCD, and because they are flipped over, so sensor is on
one side and readout on the other.
The low voltage affects dark current noise. So all else being equal the lower
voltage improves noise in the darkest sections of picture especially for long
exposure times. However, it does this at a cost of reduced quantum efficiency,
so you get less electrons/photon where there is light present, and this means
noise especially from other sources (amplifiers,A/d etc) have a greater
influence. So s/n ratio at higher light levels and shorter exposures may not be
quite as good. The reduced smearing claimed may be a useful feature for
contrasty scenes.
In general ,as the absolute pixel size goes down the readout electronics
usually occupies a bigger percent, so fill factor is particularly critical in
picture phone chips etc. but same applies as pixel war count continues to
escalate in big cameras. It may be why they brought this out for picture phone
resolution first because of very small chip size and also reduced cost with
simpler fab process.
Tim Hughes
Chuck Norcutt <chucknorcutt@xxxxxxxxxxx> wrote:
They were touting it for camera phones back then. Low voltage, low
power, greater proportion of surface area devoted to photo sensitive
area, simplified manufacturing process, readily scalable. Maybe it has
grown larger by now.
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