The cold preamplifier set-up of CUORICINO: Towards 1000 channels

We present the characterization of the cold preamplifier set-up of the CUORICINO Experiment. It consists of two single boxes located inside the cryostat, linked to the 4.2 K stage. Each box has 12 independent differential buffer channels, composed of 12 pairs of Silicon JFET transistors in source follower configuration and 48 pairs of load resistors ( 6.8 G Ω × 8 units / channel ) for thermistor biasing. The operating temperature of the JFETs is ∼ 110 K . The figure of merit of the set-up is a series input noise of about 35 nV RMS in the 0–12 Hz detector bandwidth. Parallel noise is limited only by the load resistors ( 54 G Ω ) to be about 1.2 fA RMS . In order to build a 1000 channels bolometric array a further progress in the performances of the cold stage has been studied.