| 摘要 |
PURPOSE:To omit a reference voltage generating means and to decrease the errors in comparing a displacement conversion output and a reference voltage, by using an FET in controlling a power source which charges capacitors for converting the mechanical displacement into an electric signal. CONSTITUTION:A fixed capacitor C10 and a variable capacitor C20 for displacement conversion are charged through switches S11 and S21 and a part of the FET circuit or the entire FET circuit. The opening and closing operation of the switches S11, S12, S21, and S22 are performed by the oscillation output of an oscillator OSC. When the switches S12 and S22 are turned ON, the voltages generated by discharge currents id1 and id2 of the capacitor C10 and C20 are imparted to an operation amplifier Q1. A charging current ic2 for the variable capacitor C20 is smoothed by a parallel circuit of a resistor R2 and a capacitor C2. The DC voltage comprising the product of said smoothed current Ic2 and resistance R2 is applied between the source and gate of the FETT1. The FETT1 is operated as a constant current element. |
