Source follower or charge amplifier? An experimental comparison using a detector with integrated electronics

Abstract

In spectroscopy systems where the front-end amplifier is an external circuit, charge sensitive preamplifiers have been shown to be superior in performance with respect to voltage amplifiers as the first stage of amplification. The paper studies how these two circuit configurations behave when they are integrated in high resolution semiconductor detectors of very small capacitance. This paper for the first time compares, in this new condition, the stability of amplification of the source follower with the optimum behavior of the charge preamplifier, reporting its dependence on the detector bias, on the input transistor bias, and on the operating temperature. This paper then discusses the consequent loss in linearity and resolution that a system with an integrated source follower may undergo depending on the type of reset mechanism. The point of how the instabilities of the integrated feedback capacitance limit the performance of an integrated charge amplifier is also addressed. The analysis is based on experimental results obtained with the same detector with integrated electronics used in the two different configurations.