Implementation Of Sampling Hardware Circuit And The Weak Current Signal Conditioning

Pico-ampere current often exists in high-precision scenarios such as biomedicine,nuclear technology,chip testing,and geomagnetic navigation.The development of these directions is inseparable from the detection of weak current.Research on the acquisition and detection of picoamp level current has become a research hotspot.There are the following problems in the high-precision acquisition and conditioning of picoamp-level current.Firstly,the weak current signal of picoamp level is in the same order of magnitude as the leakage current of common devices and PCBs,which has higher requirements for device selection and wiring.Pico-ampere current is not only weak,but also easily coupled with various noises during transmission and conditioning,such as electric and magnetic fields.Secondly,lock-in amplifier is often used in the field of weak current detection,and its output result often has fluctuations,which affects the detection accuracy.This thesis studies the measurement of picoamp level DC signal and lowfrequency AC signal,and completes the following research and design:(1)Conditioning circuit for picoamp level current signal.Firstly,the difficulty of high-accuracy acquisition of picoamp level current signal is analyzed,and a picoamp level current conditioning scheme is designed.Secondly,the transimpedance amplifier circuit is analyzed and designed,and the selection of key components is completed.Thirdly,the influence of device and PCB leakage current on the measurement circuit is analyzed,and a corresponding protection scheme is designed.Finally,the coupling interference of electric and magnetic fields is analyzed,and a double-layer shielding scheme is designed.(2)A method to reduce the fluctuation of output result of digital quadrature lockin amplifier is proposed.When the digital quadrature lock-in amplifier is used to detect weak current signal,the detection result often has fluctuations.It is a difficulty in this thesis to reduce the fluctuation of the output result and improve the detection accuracy.In this thesis,an improved method based on traditional digital quadrature lock-in amplifier is proposed,that is,digital quadrature lock-in amplifier based on NLMS adaptive filter.The results show that for-6d B input signal,the improved method in this thesis can be effective to reduce the volatility of the results.Finally,a pico-ampere weak current acquisition circuit is built and related tests are carried out.The experimental results show that the DC current in the range of 100 f A-2?A can be measured correctly,the measurement error is within 1%,and the highest current resolution is 1.5f A.