Research On Resistive Picoampere Micro Current Source Technology

The generation of micro-current is of great significance to the development of many fields such as aerospace,communications,medicine,biology,etc.The test of micro-current is also widely used in various scientific research and industrial fields,whether it is the generation of micro-current or the test.Do not open the micro current source.Domestic research on micro-current sources started relatively late,and the resolution and stability of mainstream micro-current source equipment are far behind those of developed countries.In response to this problem,this article carried out research on micro-current source technology,Mainly carried out the following research work:First of all,several basic circuits that can generate DC micro-current are studied,and on this basis,the design principles of foreign pico-ampere-level micro-current sources are compared and analyzed,and the resistive implementation scheme is selected,and then the entire DC micro-current source is determined.The overall design of the system.Secondly,the key technology in the design process of DC micro current source system is researched.Mainly problems such as leakage and noise.In order to solve the problem of insufficient insulation of the circuit board,PTFE insulated terminals are used in important places that need to prevent leakage;low-hygroscopic insulating paint is coated on the surface of high-value resistance(above 10~9Ω)to prevent air humidity from affecting its resistance;A double-layer shielded high-insulation relay is used to reduce the leakage current generated on the relay.The selection and use of electrometer op amp,an important device,are studied,and the noise of the system is analyzed,and noise suppression measures are proposed.Third,the hardware circuits of each part of the system are designed.A voltage source circuit based on a 16-bit pulse width digital-to-analog converter is designed,which can achieve precise adjustment of voltages in three ranges of 0.2V-20V,with a resolution of more than 1m V.The voltage-current conversion circuit is designed and simulated,and the resistors and relays of various ranges are selected.In order to ensure the ultra-low bias current characteristics of the electrometer op amp,a bootstrap voltage detection circuit is designed and a guard ring structure is adopted.The effectiveness of the structure is proved by simulation analysis.Finally,a test platform for the DC micro-current source system was built,and the upper computer program based on the LabWindows/CVI development platform and the lower computer program based on the ARM platform were written to conduct experimental research on the system.First,the output of the key sub-circuit part was tested,and then the short-term stability of the passive output and active output of the DC micro-current source system were tested.The experimental results showed that the uncertainty of the active output It is higher than the passive output,and both output results can meet the design index with the highest uncertainty of 0.5%in this design.