Equivalent Noise Charge Contribution of the √f Parallel Noise in Nuclear Spectroscopic Measurements Using Different Shaping Amplifiers

In this work, both a theoretical study and experimental measurements are shown to describe the equivalent noise charge (ENC) contribution of the parallel
$\sqrt {f}$
noise of a charge-sensitive preamplifier in a nuclear spectroscopic chain. Previous works have demonstrated that this noise is produced by the distributed capacitive coupling to bulk of the preamplifiers’ high-valued feedback resistors, which give rise to an resistive-capacitive (R-C) structure known in the literature as “diffusive line.” The introduced noise is particularly evident when such devices are integrated in a chip using a polysilicon layer that has intrinsically high distributed capacitance to the chip’s bulk. Different shaping amplifiers are taken into consideration (analog quasi-Gaussian, digital trapezoidal/triangular, and CR-RCn), and closed-form expressions of noise coefficients are given whenever possible.