A time-driven FPGA-based fast nuclear charge digitization method

Abstract

Abstract Without the need of high-speed analog-to-digital converters (ADCs), the method of translating the shape of nuclear pulses into a time width for charge measurement provides the possibility of multi-channel system implementation with commercialized discrete components. In this paper, we propose such a circuit scheme based on field programmable gate array (FPGA) to realize nuclear charge digitization. Compared with other charge digitizing methods using discrete components, the proposed scheme has a shorter measurement dead time and high measurement performance. Since some logic units of the FPGA are developed to replace discrete analog devices, only one additional analog amplifier for each channel is required outside of the FPGA, which makes the circuit scheme compact and feasible for the implementation of multi-channel systems. Combining with a positron emission tomography (PET) detector module that consists of LYSO crystals coupled with a SiPM array for 22Na coincidence measurement, the circuit can achieve the energy resolution of 12.3% with a typical measurement dead time of 500 ns. Using a reference detector with 164.7 ps time resolution, the coincidence time resolution of the two detectors is evaluated as 367.1 ps, which means the proposed circuit also has an acceptable time performance for some applications.