Design and noise analysis of charge sensitive amplifier for readout of pixelized thin film amorphous silicon sensors

Future high-energy physics experiments entail the need to improve the existing detection technologies, as well as develop new ones. Larger luminosities of the new accelerators require greater granularity of tracking detectors, which will be exposed to much higher doses of radiation. One of the newly-investigated solutions for tracking detectors is the Thin Film on ASIC (TFA) technology, which allows combining advantages of Monolithic Active Pixel and Hybrid Pixel technologies. In the paper we present noise analysis of a front-end circuit for readout of a TFA sensor. The circuit is based on a charge sensitive preamplifier built around an un-buffered cascode stage with active reset circuit. The feedback capacitance is reset through a transistor biased with a constant current instead of a voltage controlled reset transistor in order to limit parasitic charge injection into a very small feedback capacitance. Detailed analysis of noise in the reset and the readout phase and design optimization based on the Enz-Krummenacher-Vittoz (EKV) transistor models as well as test results of prototypes are presented.