One and Two Poles Compensation of Charge Sensitive Amplifiers with Resistive Feedback to Improve the Energy Resolution in GRETA

The Gamma Ray Energy Tracking Array (GRETA) is a detector system currently under construction in the US. The energy of the gamma-ray is determined in real time inside field programmable gate arrays (FPGA), employing the typical processing chain of shaper, pole-zero cancellation (PZC), baseline restoration and pulse high analysis. In this paper we propose a 2-poles PZC for GRETA based on the analysis of the charge sensitive amplifier (CSA). We derive the time and discrete domain versions of the PZC, and implemented it using floating point and integer math. We then compare the performance of 1- and 2-poles PZC for a detector and different gamma-ray rates. We observed an improvement on the full width half maximum energy (FWHM) resolution of the ⁶⁰Co 1.33 MeV line at 90 Kgammas/s for the 2-poles PZC in relation to a 1-pole PZC. Finally, we describe how the 2-pole PZC can be implemented inside an FPGA and meet the high computational rate required for GRETA.