Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!iscuva!jimc
From: jimc@iscuva.ISCS.COM (Jim Cathey)
Newsgroups: sci.electronics
Subject: Re: Batty monitors and cheap video
Message-ID: <2637@iscuva.ISCS.COM>
Date: 4 Oct 89 18:06:05 GMT
References: <57732@psuecl.bitnet> <371@galadriel.bt.co.uk>
Distribution: sci.electronics
Organization: ISC Systems Corporation, Spokane WA
Lines: 32

In article <371@galadriel.bt.co.uk> pcf@galadriel.bt.co.uk (Pete French) writes:
>No - they aint CCDS. CCDs are designer for use as a camera - and you cant
>access each bit individualy like you can with RAM, you have to shift them out
>serially. In low lighting conditions you can get bits lost in the shifting
>which explains the smears accross the picture ou get from CCDs in bad light.

Incidentally, CCD's are analog devices, each charge bucket is dumped into its
neighbor every time you hit the shift line.  There must be a slight 
degradation every time you kick the buckets, so this is probably where the
smearing comes from.  (I've never seen one, but I do remember an article
on a CCD reverb unit from old an Popular Electronics that explained the
CCD device used there).

Anybody know how they shut off the light sensitivity of the charge
buckets while the image is being shifted out?  Don't these work by the
impinging photons causing a leakaway of stored charge?  I guess they could
depend on the fact that each scanline of the device is 'exposed' for a long
time, but only read/exposed for a short time so the error would be small.

If this was the case then having the sun impinging on the drain side of
the CCD could wipe out the whole line, even if the rest of the scene
was properly exposable -- the sun being bright enough to wipe out the
charge immediately (or at least degrade it significantly).  This true?

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