High-frequence Capacitance And Inductance Measuring Method And Implementation

Along with the increasingly thriving electronics industry, the measuring demands of accuracy and circumstance for the electronic element has become much more stricter,and there is good market prospect for a low-cost, high-precision capacitance and inductance measurement instruments that works at high frequency. Based on the design of traditional measuring apparatus and combined with the application of the modern controller, the measuring system which works in the specific conditions and situations is designed in this thesis. To the strategy of test principle, after carefully compared with the Huygens bridge method(which has longer measuring period), L-C resonance method(which has lower measuring accuracy) and vector voltage-current method(voltammetry), finally, the vector voltage-current method is chosen by the demand of measuring device.In addition, the measuring apparatus has a driving signal source module which can produce sine driving signal whose frequency can be adjusted by the users freely. The signal will transform through the series circuit of standard resistors and determinand(capacitance or inductance), and we just need to measure the voltage of the driving signal and the determinand. Then through a series algorithms realized by the control unit, the value of the component under test will be calculated, and ultimately the results will be displayed on the LCD screen.In this thesis, the application and development at home and abroad of the measuring instrument is firstly introduced; then according to the requirements of the system, and after carefully comparing, the design of the hardware circuit, the measurement principle and the appropriate chips of the system are determined. This paper highlights the internal architecture and the extended resources of the controller which uses STC90C516 as core, and explains the circuit of driving signal which uses the DDS chip AD9850 as core and its control method, furthermore, the conversion algorithm is derived in detail. This paper also focuses on high frequency parasitic effect of the capacitor and inductor, and analyses the control flow of program in this measuring system in detail, and conducts the modular programming, then by using the central processing unit to assign each control module. Finally, by using the device of developed for the measurement of high-frequency capacitor and inductor, the results arerecorded and the discrepancy is analysed. And the result shows that the design of the measuring equipment can meet the basic requirements.