An Embedded FPGA Design for Double-Time-Over-Threshold (DToT) Measurement

This study presents a novel embedded FPGA design utilizing Time-over-Threshold (ToT) and Double-Time-over-Threshold (DToT) methods, addressing the limitations of traditional analog-to-digital converters (ADCs). The ToT method has gained popularity due to its advantages in power consumption, cost, and integration, yet it faces challenges such as energy vs. time resolution trade-offs and signal nonlinearity. The proposed DToT method aims to mitigate these issues by employing two thresholds, offering improved energy resolution and reduced nonlinearity compared to single-threshold ToT methods. The system is implemented on a Zynq System-on-Chip (SoC) that integrates an FPGA with an ARM CPU, enabling dynamically adjustable thresholds, high-precision timing measurements, and flexible data processing capabilities. The evaluation was conducted using a CAEN DT4800 Digital Detector Emulator, which generated signals from a 3-inch NaI detector exposed to a 22Na radioactive source. The results demonstrate the superior precision of the DToT method, particularly at lower energies, with σ/μ ratios of 1.82% and 3.82% for the 511 keV and 1275 keV peaks, respectively. This FPGA-based approach provides a versatile and high-precision solution for instrumentation applications, offering significant advantages over traditional ADCs and single-threshold ToT methods. The integration of an ARM CPU with FPGA logic allows for flexible and tunable signal processing, making it suitable for a wide range of applications, including particle physics experiments, medical imaging systems, and industrial sensors. The study underscores the potential of DToT for high-resolution spectroscopy and suggests areas for future research, such as optimizing the system for specific experimental setups in scintillation gamma cameras or positron emission tomography (PET).