Automatic pole-zero/zero-pole digital compensator for high-resolution spectroscopy: design and experiments

In a high-resolution spectroscopy system the relatively long exponential decay due to the charge preamplifier is customarily cancelled in an analogue fashion by means of a PZ (pole-zero) stage. The accurateness of such a compensation has a big impact on the energy resolution because it strongly affects the baseline-stability problems. We have automatically and on-line performed such a compensation in a digital way, while maintaining a spectroscopy performance and keeping at minimum both the ADC sampling frequency (thus power consumption) and its resolution (thus cost). This is done through an IIR filter, implemented within a FPGA by a DSP. The so-compensated waveform has, in excellent approximation, an all-pole shape. Starting from such a signal, the minimum-noise filters for energy and/or time measurements are then promptly synthesized and implemented for real time operation through the same DSP.