Optimization of digital spectrometers using a pulse streaming generator

Abstract

This paper presents a digital pulse streaming generator developed to test and optimize the design of real-time digital spectrometers. The purpose of this generator is to produce a stream of digital data capable of reproducing the typical pulse response of a pre-amplifier used with solid state or other radiation detectors. This process not only avoids the use of X-ray sources during the test and calibration procedures as it also allows the experimentalist to take in account as many stream pulse scenarios as he desires. Using this tool it is possible to simulate a number of signal parameters that are characteristics of each front-end electronic apparatus. Such parameters include pulse amplitude distribution, rise-time components, decay-time of RC feedback pre-amps, frequency of occurrence, ballistic deficit, etc., as well as noise parameters (amplitude, power spectra density, type, etc.). In order to test a specific digital spectrometer implementation, this generator includes step, delta and optionally 1/|f | noise sources. Pulse pile-up effects arise due to the fact that we use a Poisson distribution to reproduce a real stream of events. The digital data stream is directly fed into the FPGA reproducing the behavior of the fast acquisition channel (FADC) of the spectrometer. This is an important auxiliary tool to the design and debug of the FPGA, namely when the implementation of near-optimum signal-to-noise ratio filters is desired.