Low-noise CMOS charge preamplifier for X-ray spectroscopy detectors

The development of radiation detectors for high-resolution high-rate X-ray spectroscopy is strictly related to the continuous improvement of the performances of the related front-end readout electronics. Beside the excellent performances achievable by the integration of the front-end transistor in the detector chip, as successfully obtained in silicon drift detectors with on-chip JFET, many detector solutions still adopt a technologically simplest solution based on the connection of the given detector to an external low-noise JFET. Recently, it has been shown by different authors that a fully monolithic CMOS preamplifier with a PMOSFET input may achieve very interesting noise figures when directly connected to radiation detectors. In this work, we have designed a low-noise CMOS charge preamplifier for high-resolution X-ray spectroscopy and we have compared its performance with the one achievable by using an external JFET. Despite the intrinsically higher 1/f noise coefficient, a suitable optimization of the input transistor in terms of transconductance and input capacitance, for a given detector, still allows to target superior performances with respect to a state-of-the-art external JFET solution. We have realized a first prototype of the circuit and its performances are presented in this work.