| 摘要 |
PURPOSE:To eliminate the effect of stray capacitance, by making oscillation for static capacitances in series connection at least one of which is changed in response to the change in physical quantity through alternate changeover and controlling an applied voltage to the static capacitance with a counting value of the output. CONSTITUTION:A sensor 11 is provided with a movable electrode 11a moving according to the change in physical quantity, a fixed electrode 11b, and a fixed electrode 11c located between the electrodes 11a and 11b. The electrode 11c is connected to an inverting amplifier 12 and the electrodes 11a and 11b are respectively connected to the output terminals of NAND gates 13 and 14. An oscillation circuit 18 consists of the sensor 11, gates 13 and 14, an amplifier 12 and a resistor 15, and an output of an integrating circuit 17 is connected to a positive power supply terminal of the gate 13. The circuit 18 is switched with an FF16, and frequencies determined with a capacitance C3 of the electrode 11a and a capacitance C4 of the electrode 11b are switched and oscillated, and a Q output of the FF16 is supplied to an integration circuit 17 via a smoothing circuit 22. The output voltage V of the circuit 17 is a value proportional to C4 versus C3, allowing to eliminate the effect of stray capacitance. |
