Greetings!
I'm a research scientists with the Johns Hopkins University, and I'm
working on a set of designs for an X-ray detector, and trying to spec
out various methods for obtaining the data we need. One of the designs
is a system based on diode arrays + amplifiers + ADC system. I've
already got a good handle on the detector end, and the data
acquisition system, but I'm stuck on the amplifier system.
We've used commercial amplifiers in the past, but they would likely be
overkill for our situation, and end up quite pricey on a cost/channel
basis. Given our specifications, I'm wondering if the optimal solution
would be to pay for a consultant to develop and test a design
specifically for our application, and then take that design and punch
out the number of boards that we would need.
Our generic needs seem to be fairly modest, 100-250kHz bandwidth with
a gain of 10^7, but as always the devil is in the details. Naturally,
we want the lowest noise possible so that we can measure signals at
the nA or sub-nA level.
So, here's the question. Are the specifications and schematic sketch
shown here:
http://picasaweb.google.com/ktritz/PhotodiodeAmplifierDesign/photo#5218836415390875906
adequate for a professional to provide a consultation estimate? Would
the amplifiers be simple enough that a 2nd year EE student could
manage the design, or are we talking about skirting the bleeding edge?
I'm never contracted a consultant before, so should I expect a
consulting price tag of $1000? $10000? I'm working with a budget
that's higher than a hobbyist, but not quite cor****ation level.
I would also be happy to discuss specific amplifier design ideas.
Given the capacitance of the detectors in question, I would imagine
that a very low voltage noise opamp is the way to go, or perhaps a
JFET front end. The BF862 looks pretty good, and it's relatively high
capacitance wouldn't matter much compared to the diode.
Thanks,
Kevin
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