GeFRO, a new front-end approach for the phase II of the GERDA experiment

A novel approach was developed for the readout of ionization detectors in cryogenic environments. It was proposed for the phase II of the GERDA experiment at LNGS, and it is currently under test by the GERDA collaboration. The readout scheme consists of a JFET and a diode operated at cold, close to the detector for the best noise performances, and of a remote second stage of amplification located at room temperature. The second stage provides a slow feedback loop through the diode to discharge the input node after each event. The fact that only two components are located at cold allows to minimize the amount of mass contributed by the electronics close to the detector: this is a very remarkable aspect when radiopurity issues are concerned. The first prototype was named GeFRO (Germanium FROnt-end), and it was successfully tested with a coaxial High Purity Germanium detector of 20 pF capacitance from GERDA phase I, obtaining a zero-energy resolution of 1.1 keV, and with a Broad Energy Germanium detector of about 1 pF from GERDA phase II, where the zero energy resolution improved to 0.95 keV thanks to the reduced detector capacitance.