At 03:26 PM 4/17/2004, you wrote:
>Re: Noise.
>
>The noise is usually created by optical trickery inside the CCD, usually
>attributed to the design and lithography quality of chip. As the process
>becomes smaller and more precise, the quality of the itty-bitty photodiodes
>should increase as well.
I've done analog CMOS IC design for 26 years and I have no idea
about these theories. Noise come from dark current, interface states
at the oxide-silicon interface, thermal phonons, hole electron
recombination... It helps to have a clean process with well annealed
silicon, but noise and minimum feature size are not necessarily related.
Larger active area averages more of the noise with a larger signal,
resulting in higher signal to noise. For any given silicon process - a
smaller pixel area will give more noise; smaller in analog circuits
always comes with more noise. There are noise sources in silicon
that are inherent to silicon circuits no matter what the process,
lithography, feature size, etc.
All of the best performing cameras/CCD sensors all have a pixel size
around 8um x 8um. I have not seen one camera with smaller pixel sizes
that also has better signal to noise performance. There are only so many
photons to catch, bigger pixels catch more photons,.
Wayne
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