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Photon Detector Assembly "Front-End" Electronics
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Figure 13.
Simplified
Electronics Diagram Showing the
Detector and the "Front End" of the Preamplifier
in a
Cryogenically Cooled Ge or Si(Li) Detector. The
feedback element may be either a
resistor or instead
an electronic switch that resets the FET gate voltage to
zero whenever a given threshold voltage is reached. |
The front-end electronics (Fig. 13) include the input field-effect
transistor (FET) and the feedback element of the charge-sensitive preamplifier. The
feedback element comprises a capacitor and a resistor (passive
feedback) or a transistor
(active feedback). Preamplifiers with active feedback, such as the transistor-reset
preamplifier (TRP), are used for achieving ultra-high count rates.A temperature-sensing element, also located in the cryogenic vacuum
enclosure, automatically shuts off the HV power supply if the detector temperature begins
to rise. The front-end electronics are enclosed in the cryogenically-cooled enclosure to
minimize electronic noise. Both the input FET and the feedback element have optimum noise
characteristics at ~120 K.
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