This study aims to design and develop a novel charge-sensitive preamplifier by using N-channel junction field effect transistor and RC (Resistor-Capacitance) low-pass network instead of traditional high resistance feedback resistor.

A junction field-effect transistor and an integrated operational amplifier were used to form an amplifying circuit with advantages of high input impedance and large open-loop gain. A high-pass loop was formed by a small capacitance capacitor to provide a high-frequency feedback loop for the circuit and integrates nuclear pulse current at the same time. The RC low-pass network constituted a DC (direct current) feedback loop to provide a stable DC operating point for the circuit, and a voltage divider for the N-channel junction field effect transistor operating in a forward bias state to realize a feedback capacitor for continuous discharge of its charge.

The charge-sensitive preamplifier was connected with BPX66 Si-PIN detector and the ²⁴¹Am source was measured at room temperature. The energy resolution of 3.03%@59.5 keV was achieved.

Compared with the traditional resistive capacitance feedback charge-sensitive amplifier, this circuit can effectively over-come the noise introduced by the large-resistance feedback resistor, especially for semiconductor detectors such as Si-PIN.