For those eager to study charge sensitve preamps or even build one, check out John Hendron's recent "links forum" posting on Ortec manuals on-line.
When there, down load the Ortec 109 preamp. (1 FET and 11 transistors.) I have this preamp and it works great! The whole manual is nice, but if you just want the schematics and block diagram, print only pages 18 and 19.
Most of the components are not critical. The wiring is critical in the "front end" area and shielding is a must. The toughest component to get from normal sources is going to be the 100meg bias resistor. The FET can be most any common N channel JFET. This amp is not only good for solid state detectors, but GeLi detectors and BF3 tubes.
Ideally, the best noise figure and the least hassle will be had if the circuit is constructed in the same housing with the detector. (no cabling)
Richard Hull
Charge sensitive amplifier schematic
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Richard Hull
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Charge sensitive amplifier schematic
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
-
guest
Re: Charge sensitive amplifier schematic
I've had a look at this schematic (Ortec 109), and it's very 60's in its approach. It was designed when people were stilll getting used to working with transistors versus tubes (most of the seasoned engineers of that time probably still had a foot in both camps), and the first commercially available IC op amps had just been released. The amp has three basic functional blocks. The last two have no mystery about them, but the first stage has some oddities that bear looking into. I am finding it difficult to reconcile the claim of 20,000 open loop gain with the simple structure of the circuit, unless regeneration is somehow involved. When I have some time, I will run the first stage amplifier through some simulation to get some more insight on what is happening. Simulation does not substitute for actually getting a circuit running on the bench, but it's a valuable tool in the initial stages of a design, and has helped me make my bench time much more profitable.