A Low-Noise Charge Sensitive Preamplifier for Semiconductor Detectors Using Paralleled Field-Effect-Transistors

The use of a 2N3823 or a 2N3819 (the Silex equivalent of the 2N3823) field-effect transistor (FET) has led to the design of an improved charge sensitive preamplifier. The amplifier has provisions for paralleling FET´s in the input stage which gives considerable improvement in the resolution vs capacitance slope over single FET´s. Measured resolution of the amplifier temperature was 0.53 keV(Ge) + 0.046 keV/pF with a single FET in the input stage and 0.91 keV + 0.023 keV/pF with four paralleled FET´s in the input stage. Cooling the FET´s to 140°K gave 0.36 keV (Ge) + 0.030 keV/pF with a single FET and 0.62 keV(Ge) + 0.017 keV/pF with four paralleled FET´s. Theoretical computations of the expected resolution gave excellent correlation with the results from the measured circuit.