Re: Autoguider reference
Schrock (schrock@stout.kodak.com)
Tue, 2 May 95 12:14:37 EDT
Aart Olsen wrote:
>
>Chuck Grant writes:
>
>>I thought photodiodes were operated reverse biased and
>>a photon caused current to flow across the junction.
>
>Avalanche and PIN photodiodes are reverse biased. Photons release held-back
>electrons to permit current to flow. They are very fast but noisy.
>Avalance diodes are analagous to photomultiplier tubes, where there is a
>huge amount of amplification built in (electons cascade and release more
>electrons). PIN diodes are used for fiber optic communication. Most low
>light applications use photodiodes in what is called the photovoltaic mode.
>Photons collide with the silicon, causing electrons to separate and they in
>turn migrate favorably to one of the junctions (I can't remember which one).
>Because there is no bias there is no leakage, nor shot noise from escaping
>electrons, and they're very low noise devices. PV mode is the way the
>common, voltage producing photocell in a calculator works. Unlike a CCD
>element, the PV cell isn't made to have its own substantial capacitance, so
>an external capacitor has to be used if you want to store charge, but in
>principle it's the same process.
>
>
>Aart M. Olsen aart@uiuc.edu 217-333-7467
>College of Veterinary Medicine Univ of Illinois at Urbana-Champaign
>
>
My understanding of CCD photodiodes was that the electrons from the photodiode
are drained into the charge well of the CCD. IF the well overflows, blooming
can occur unless an antiblooming gate strips off overflow charge. Once the
CCD integration time is complete, then the charge is transferred out. The
different transfer modes that I can think of off the top of my head are
full frame and interline transfer (for a 2-D CCD)
Tony Schrock e-mail: schrock@kodak.com
Advanced Systems Lab
Electronic Systems Division
Imaging Research Laboratories It is better to meet a mother bear who has
2-65 KRL lost her cubs than a fool in the middle of
Eastman Kodak Company a stupid project. Proverbs 17:12
Rochester, NY, 14650-1821
The opinions expressed here are not those of Eastman Kodak. I'm just here
to take on the mother bears.