Design of a Low Noise and Low Background Charge Sensitive Amplifier for the Readout of Germanium Detectors

The observation of neutrinoless double beta decay would have major implications in the understanding of the origin of the matter in the universe. Given zero electric charge and no colour, they may be Majorana particles, i.e. their own antiparticles. The Large Enriched Germanium Experiment for Neutrinoless double beta Decay (LEGEND) is a ton-scale experimental program to search for the neutrinoless decay in the isotope 76 Ge. In this framework, we have designed a new ASIC in the 0.35 µm CMOS technology, which will fulfill Ge-detector requirements. The ASIC has a key role in order to obtain a good energy resolution and a high radiopurity environment that are crucial conditions in neutrinoless double beta decay experiments. The ASIC has been designed featuring a low noise Charge Sensitive Amplifier (CSA) and an on-chip Low-DropOut regulator (LDO). The LDO allows the chip to be powered without bypass capacitors which are not compliant with the radiopurity requirement. With a 50 pA leakage current and a detector capacitance of 4 pF, the ASIC shows a noise performance of 50 e−rms. In this work, we also present the simulated transient response of the CSA. In the end a dedicated Line Driver circuit drives the signal in a differential way over a distance of about 10 m.