Capacitance Measuring System Based on Modified Sigma-Delta Converter

Abstrac t- The paper brings new information about capacitance measuring system based on modified sigma-delta converter (MSDC) with compensated loop based on phase locked loop (PLL). The consist of the 2 current sources and can be used for non-electrical quantity which will break the value symmetry in circuit, e.g. light intensity can be also measured with photodiode connected parallel to current source. Measuring system can work in open loop (direct sigma-delta converter) or closed loop (PLL). The system has the voltage and digital output and in closed loop can be supposed as a voltage controlled oscillator which is locked to input clock frequency. The simple flip-flop sensor for capacitance, or some other measuring is also described. In this paper, short information concerning of the system and experimental results are shown