Design of an integrated low-noise, low-power charge sensitive preamplifier for gamma and particle spectroscopy with solid state detectors

The design of an integrated charge-sensitive preamplifier suitable for γ-ray spectroscopy is presented. It is fully integrated, except for the feedback resistor, and can drive directly a 50Ω cable with its low impedance output stage. It is designed in AMS 0.35μm technology and its small dimensions and low power consumption (10 mW) are optimized for multi-channel applications. It works both with germanium and silicon detectors for a large range of values of electrode and feedback capacitances. Its wide bandwidth ensures a risetime of 10 ns or less in most configurations. This characteristic makes the preamplifier suitable not only for high resolution spectroscopy but also for pulse-shape analysis. The most innovative part of the circuit is the input stage: generally in the field of γ spectroscopy a discrete low-noise JFET transistor is used, but this structure fails when physical dimensions and power consumptions are a concern. This fully-integrated input stage was designed in order to keep the noise parameters comparable with state of the art levels, and was conceived with flexibility in mind. It features a differential input structure, variable bandwidth and adjustable operation point.