A Novel Read-Out Electronics Design Based on 1-Bit Sigma-Delta Modulation

The conventional front-end electronics for PET imaging consist of an energy circuit and a timing circuit. A single channel in front-end electronics typically requires several amplifiers, an ADC and a TDC. In this paper, we present a novel front-end electronic design using 1-bit sigma-delta (Σ-Δ) modulation and an FPGA. The new design requires only one analog amplifier per channel. The output of the analog amplifier is read directly by the FPGA. Both the energy and timing calculation are implemented in FPGA firmware. The scope of this paper is to introduce the novel design in detail and to evaluate its performance in energy and dark current measurements. Simulink simulations were performed to validate the design with ideal components. A one-channel prototype circuit was built to assess the design with real components. The prototype circuit was tested with different input signals, including test pulses, pulse signals from a PMT detector, DC current signals and dark current signals from an SiPM sensor. Both the simulation and experimental results show that the method is inherently stable and has excellent accuracy and linearity in energy and dark current measurements. The prototype analog board was built with discrete components cost about $ 0.5 in total. The power consumption was about 20 mW. We conclude that the new method provides a cost-efficient and power-efficient way to accurately measure the energies of analog pulses and dark currents from detectors. The timing performance of this method is currently under evaluation.