The Readout and Biasing System for the MARE Experiment in Milan

The complete readout and biasing system for the MARE experiment in Milan is presented. The experiment aims at a direct measurement of the neutrino mass, and is based on an array of microcalorimeters coupled to semiconductor thermistors. The readout is based on JFETs operated inside the cryostat at cold (130 K), to buffer the voltage signal from the thermistors. The sources of the JFETs are fed into second stage amplifiers with very low noise (less than 0.5 nV/Hz−−√ white noise) and programmable high gain. The outputs are then processed by Bessel filters and acquired with a commercial DAQ system. Every 20 channels, an additional group of 4 is used to amplify the ground reference from inside the cryostat; this common ground signal is then subtracted from each channel. This approach allows to recover a fully differential readout with a smaller number of cables with respect to the standard differential configuration. The detector bias is programmable in voltage and sign with 8-bit resolution. A test signal can be superimposed on the bias voltage, in order to test each channel individually. All the readout system is remotely programmable from a PC, coupled through optical fibers.