High-accuracy fit of the poles of spectroscopy amplifiers designed for mixed analog-digital filtering

In this paper, a method for the identification of the poles' and zeros' position of an analog amplifier for nuclear spectroscopy used as a prefilter for a subsequent digital filter setup is presented. The proposed technique is based upon a subspace-based system state-space identification (4SID) method, which is well suited to a data set constituted by a noisy measurement of the sampled impulse response of the circuit. The algorithm runs unassisted and does not require skills by the operator. The experiments confirm that by using the so-obtained pole values, the shape of the impulse response of the amplifier can be fit with much better than 1% accuracy. Consequently, the overall filtering (analog+digital) can have finite duration and a top with a flatness much better than 1%.