Design Of FPGA-Based Weak Current Detection System

Over the past few decades,significant progress has been made by humankind in the fields of science and technology.As a result,there have been substantial changes in people’s lifestyles,and the environmental challenges that come along with technological,industrial,and societal advancements have become more pressing.Among these issues,radioactive pollution is particularly unique and requires special attention.In nuclear physics,various nuclear signal detectors have been used to detect radioactive materials.However,detecting weak radioactive substances poses greater challenges due to the small amplitudes of these signals.The lock-in amplifier uses correlation detection as the core principle and further selects the detection interval,as they have high detection capabilities and have become a common means of detection in various research fields.Field-Programmable Gate Arrays(FPGAs)are integrated circuits known for their flexibility and reconfigurability,allowing for specific functionalities to be implemented through programming.The programmability of FPGAs makes them a versatile,cost-effective,and efficient solution applicable to various applications.FPGAs have been widely used in signal processing for precise data acquisition and real-time data processing.This article focuses primarily on the detection of weak current signals.It first introduces the influencing factors of weak signal detection and various common methods for weak signal detection.Subsequently,an introduction to the lock-in amplifier designed for this experiment is provided.The alternating current modulation is used in the pre-signal processing module to convert the current signal to a voltage signal,which is then amplified by the pre-amplifier to a level recognizable by the analog-to-digital converter.The principles of the core module of the lock-in amplifier,the phase-sensitive detector,and the subsequent demodulation are analyzed based on theoretical foundations.A simulation platform for a digital signal processing system was built using MATLAB to validate the feasibility of the system.To enhance the system’s capability to detect weak signals and reduce the impact of background noise and drift caused by analog components such as chips,a digital lock-in amplifier was designed.A digital signal processing system on the DE2-115 FPGA platform was also designed.Experimental data was used to plot the input-output linear relationship of the system under different operating conditions.It was found that under working conditions where the input signal-to-noise ratio is-10 d B,the system can identify weak signals submerged in noise.Under working conditions where the input signal-to-noise ratio is-3 to-10 d B,the system can respond quickly to abrupt signal changes.