Very high performance stabilization and data acquisition systems for the COSINUS experiment

The COSINUS collaboration aims to develop a cryogenic scintillating calorimeter for the search of dark matter, using undoped sodium iodide crystals as target. The simultaneous measurement of the phonon and light signal - both read out by Transition Edge Sensors (TESs) - allows to discriminate between signal and background events. For proper functioning, TESs have to operate close to their characteristic transition temperature, hence there is the need for a programmable, very stable and high resolution working point stabilization and biasing system. For this purpose, we designed a flexible 2-channel custom board, which is able to generate a programmable current with a 12-bit resolution. Current full-scale ranges can be further selected with 5 bits, for better flexibility during detector characterization. Each channel can be used for both TES biasing and TES temperature stabilization via a dedicated heater. The same board is also able to inject custom-shaped current pulses into the heater, in order to periodically calibrate the energy response of the detector and to calibrate the TES transition point. The thermal drifts are compensated using an 8-bit trimmer, reaching a stability over temperature of less than 1 ppm/°C. The board is based on a Cortex-M3 microcontroller and is remotely controlled through an optically connected CAN bus. We also designed a prototypal signal filtering and digitization board, which consist of a 12-channel 6-pole Bessel filter with programmable cut-off frequencies between 24 Hz and 2.4 kHz. An onboard 50 ksps ADC with an effective RMS resolution of 20.2 bits is responsible of the signal digitization. In this contribution, we present the design solutions and performance of these two electronic apparatus: the stabilization system for the COSINUS detector and the prototype signal filtering and digitization system.