LOW NOISE AMPLIFIER FOR HIGH RESOLUTION X -RAY SPECTROSCOPY USING GERMANIUM NTD MICROCALORIMETER

In this paper I describe the main features and operational parameters of a low noise amplifier designed for X -ray microcalorimeters with a NTD (Neutron Transmutation -Doped) germanium resistive sensor and I present some of the solutions that we have adopted to implement this low noise amplifier inside an Adiabatic Demagnetisation Refrigerator (ADR). Microcalorimeters operating at cryogenic temperatures ensure high spectral resolution as well as high efficiency and are therefore detectors extremely important for applications in X -ray Astronomy to investigate the physics of cosmic sources. These characteristics impose severe restrictions on the additional noise, due to the electronic conversion of the signal pulse.