A Parametric Radiation Detector Preamplifier

A charge-sensitive preamplifier has been built employing a pair of varactor diodes in a novel parametric amplifier configuration as the first amplifying element. The circuit consists of a parametric subharmonic oscillator, pumped at about 130 Mc included in a negative feedback loop. Input charge signals perturb the oscillator tuning. The feedback circuit prevents significant change in the oscillator amplitude by supplying an approximately equal, opposite charge to the input circuit through a small feedback capacitor. The following noise performance, referred to germanium detectors, has been obtained. Temperature FWHM Slope 300°K 1.40 keV 20 ev/pF 77°K 0.64 keV 13 ev/pF