Impedance-Voltage Converter Consisting of Positive Feedback System
Michio Kudo, Shoichi Takeda · Transactions of the Society of Instrument and Control Engineers · 1974
In this report, we investigated an impedancevoltage converter consisting of a positive feedback system.The standard signal is led to the positive feedback system as input. And we proved that in the above system, with the necessary circuit condition satisfied, the conversion output is obtained in proportion to the unknown impedance level in exactness. Then we made clear the circuit design process of the above circuit condition at the signal frequency. At the same time, we considered the stabilization of the above condition, since variation of the condition affects the output directly.We cleared the stability condition of the feedback system quantitatively. Thus within the stable domain, unknown impedances in a wide range can be stably converted to the output voltages, and also these output levels can be easily adjusted by exchanging the standard resistance. In this case, moreover, we reduced negligibly the error of conversion by restricting the levels of unknown impedances compared to the input and output impedances of the amplifiers in the system.As the standard signal source, we prepared a two-phase oscillator. In this, a stable output was gained by using a nonlinear element controlled by the oscillation level. Moreover the oscillation output was led to a synchronous detector as a reference voltage for the purpose of demodulating the A.C-input from the positive feedback system to the D.C-output.We designed quantitatively the impedance converter as an example and verified the proportionality between unknown impedance levels and conversion D.C-outputs in measurement.