Low noise cryogenic electronics : preamplifier configurations with feedback on the bolometer

We discuss the various electronic configurations one can use to readout resistive bolometers such as those based on Neutron Transmuted Doped Germanium thermometers (so called NTD Ge thermometers)[1] or NbSi thin film thermometers [2, 3]. The simple voltage amplifier configuration, is compared to readout configurations with feedback on the bolometer. Using the adiabatic thermal model of bolometer as a guide for computations, it is shown that feedback readout configurations allow a natural calibration of the detector and readout electronics. Furthermore, these configurations simplify the design and improve performance of detection such as bandwidth and relaxation time. Finally we show that looped readout configurations may improve the signal to noise ratio.