Operation of traditional methods of micro resistance measuring are complicated

and it has great influence on result of the micro resistance testing. The designed micro tester AC constant current source excitation based on the tester by AC excitation source

digital phase shifter circuit

signal conditioning circuit and A/D conversion and display circuit is composed of four parts. Micro resistance by AC excitation source into AC signal through high impedance low noise amplifier AD620 to extract the response signal

and then after AD630 phaselocked amplifier circuit which measured the true response voltage signal after locking to overcome the influence of noise and external electromagnetic interference in a large extent

can realize the accurate measurement of small resistance. Through the test and comparison of the prototype nominal value

results show that the instrument works stably

has high measuring accuracy

convenient to carry and use.