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.