The preamplifier for CUORE, an array of large mass bolometers

We present the preamplifier for the readout of the 988 large mass bolometers of the CUORE experiment. Each bolometer is based on a 750 g TeO₂ crystal on which a Nuclear Transmutation Doped Ge thermistor, NTD Ge, is glued, in good thermal contact. To read out the detectors we have developed a differential voltage sensitive preamplifier based on a well selected and properly biased input JFET and by a circuit solution based on operational amplifiers. The developed preamplifier has a very small parallel noise, 0.094 fA/¿Hz, and a small voltage noise of 4.9 nV/¿Hz at 1 Hz and white noise of 3 nV/¿Hz. To allow the DC readout of bolometric detectors, the preamplifier has added a circuit for the compensation of the detector bias and the offset of the input JFET pair. An additional compensation circuit allows to minimize the voltage thermal drift. The common mode rejection ratio is digitally adjustable. DC coupling, low noise, small thermal drift and CMRR are stringent requirements of the CUORE experiment. We will describe in detail the circuit solutions and the selection criteria for devices used.