Setup of cryogenic front-end electronic systems for germanium detectors read-out

Front-end electronic devices for the read-out of ionizing radiation detectors must operate in many cases at cryogenic temperatures. In this work we focus in particular on front-end read-out systems for high-purity germanium (HPGe) detectors, which are usually operated at liquid nitrogen (LN) temperature. We analyze the strong effects that the changed characteristics of the electronic active and passive devices have on the charge preamplifier performance when operated in LN, while taking into account the particularly challenging requirements that the circuit has to meet: radio-purity, physical reliability under thermal cycling, low noise (0.1-0.2% resolutions) and fast rise time (~20 ns) needed for pulse shape analysis applications. The developed circuit consists of an external silicon JFET (junction field effect transistor), an external feedback network, and an ASIC (application specific integrated circuit) realized in a 5 V 0.8 ¿m CMOS technology. This work has been carried on in the framework of the GERDA experiment (GERmanium Detector Array). We will focus in particular on the effects that this challenging cryogenic setup has on the preamplifier performances.