Re: [ATM] Infrared Scope Design

["Bob May" <rmay@nethere.com>]

Dominic, the TV sensors come from the fact that they are
detecting an AC signal out of the steady background.  Thus it
doesn't matter so much how much ITR there is in a room  )and with
incadescent light technology, there can be a real lot, especially
if a bright bulb is very close to the TB) and the ultimate
sensitivity depends upon the rejection of the line freq.  and the
gain of the AC stages to the signal detector.  Ultimately thogh,
those IR modules don't end up being good sensors because they
first need a chopper of the incoming signal to even see the light
as such and then they need to have that signal of a fairly low
intensity in order to keep the gain stages in their linear
region.  Most of them end up with a banb, bang output form rail
to rail of the Power supply.  What is needed is a real
commparison between two photosensors to eliminage the dark
current of the photosensors and a multidecade log amp to handle
the current difference between the two photosensorsfor the
incoming signal.  chopping the signal would mean that the
detector system will be more sensitive to accuracy which would be
helpful.
Please also note that such detectors are basically instant
response rather than the timed response that a CCD array or
bolometer array can provide.  In other words, there is no light
collection time as with the CCD.
Bob May
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