Research On Weak Current Amplifier Based On Phase-sensitive Detection Of AC Modulation Technology

These years,with the advancement of science and technology,the detection of weak signals has also been better developed,and its technology has also been applied to many fields,such as cosmic ray detection,biological signal detection,radar,acoustic/optical signal detection,geological detection and so on.There are many methods for detecting weak signals.Among them,the lock-in amplifier based on phase-sensitive detection has become a common detection method due to its high-performance detection ability,and general lock-in amplifier equipment has been developed.For the detection of weak signals,the use of general lock-in amplifier equipment is somewhat insufficient.Regarding the p A-level weak current signal output by the integrating ionization chamber,how to obtain the required useful signal from the strong background noise,the lock-in amplification technology will be the key.This article mainly focuses on the detection of weak current signals,first introduces the composition,working principle and working characteristics of the integrating ionization chamber,and then analyzes the principles and theoretical foundations of analog modulation type low current amplifiers and digital modulation type low current amplifiers;Based on these theories,from both analog and digital perspectives,an analog weak current amplification system and a digital weak current amplification system have been designed and verified by experiments;the main principle is to integrate the weak current signal output by the ionization chamber and pass the exchange The modulation technology modulates into an AC voltage signal,and then obtains the required useful signal through an analog weak current amplification system or a digital weak current amplification system.In order to improve the detection capability of the system and reduce the influence of factors such as bias voltage and background noise brought by the chip,based on the analog low current amplification system,using FPGA as the digital processing chip,a digital low current amplification system is designed.The analog weak current amplification system and the digital weak current amplification system were verified by experiments;the nuclear signal experiment was done first,that is,the current source was used to output a weak current signal of the order of p A,and then it was passed through the two designed systems.As a result,Experiments show that the sensitivity of these two systems has reached 10^-13A,and has a good linear relationship,which are 0.97716 and 0.99372,respectively.After that,in order to verify the reliability of the two systems in practical applications,a radioactive source experiment was performed.The integrating ionization chamber was connected to the two systems to detect the?rays emitted by the tritium target,and the integral was plotted based on the experimental data.The saturation characteristic curve of the ionization chamber,and the saturation area(flat area)of the integrating ionization chamber is found,which shows that these two systems can be used as detection systems for radioactive materials.