Charge-sensitive preamplifier with continuous reset by means of the gate-to-drain current of the JFET integrated on the detector

In this paper, we present a charge-sensitive preamplifier designed for a silicon drift detector (SDD), where both input n-JFET and feedback capacitor are integrated directly on the detector chip. The integration of these devices allows obtaining a capacitive matching between detector and front-end transistor and to minimize the stray capacitances of the connections. A continuous discharging mechanism for the leakage current and for the signal charge is obtained by means of the gate-to-drain current of the front-end JFET. This current is originated by a "weak" avalanche breakdown mechanism, which occurs in a high-field region of the transistor channel. The advantage arising from the use of this mechanism is that the discharge is obtained directly by means of the front-end transistor without the need of any additional integrated device. A feedback loop in the charge preamplifier sets the suitable value of drain-gate voltage necessary to compensate for variations of the leakage current to be discharged. The first results of the experimental characterization of the SDD + preamplifier system are presented here.