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

We have developed preamplifier configurations used to readout resistive bolometers such as those based on neutron transmuted doped Germanium thermometers (so-called NTD Ge thermometers) or NbSi thin film thermometers. We introduce the impedance regulating preamplifier configuration. This configuration is compared to previously proposed readout configurations with feedback on the bolometer. It is shown that the impedance regulating preamplifier achieves extreme electrothermal feedback without using transition edge thermometer and SQUID readout. Thus the detector and readout electronics are straightforwardly calibrated and can handle much larger event rates. Looped configurations simplify the design and improve performance of detection such as bandwidth. Finally, we analyze the impedance regulating amplifier noise contributions, with JFETs as front-end devices, relative to other configurations.