Characterization 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 76Ge. 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). Two different versions of the CSA has been implemented. One has a dedicated compensation network and implements an integrated large value resistor through an ICON cell. The other CSA works with a large external feedback resistor. The LDO allows the chip to be powered without by-pass capacitors which are not compliant with the radiopurity requirement. With a 50 pA leakage current and a detector capacitance of 4 pF, the ASIC aims to achieve a noise performance of 50 e − rms. This work shows the results of the experimental characterization of the ASIC. We report the measured characteristic Output Voltage vs Input Voltage (external power supply) at room temperature of the LDO and the measured transient response of the CSA, showing characteristics in line with the predictions.