| 摘要 |
PROBLEM TO BE SOLVED: To obtain a capacitance-type detecting apparatus which prevents the noise and the drift of a sensor output from being amplified and output. SOLUTION: The apparatus comprises a square-wave generator 6. The apparatus is composed of a phase conversion circuit 41 by which the output of the square-wave generator 6 is converted into sawtooth waves through a time constant circuit so as to be input to a threshold circuit and which outputs square waves whose phase is delayed by a prescribed time τ3. The apparatus is composed of a synchronous frequency divider circuit 42 by which the output of the square-wave generator 6 is frequency-divided to 1/2 so as to generate a sensor driving signal SD and by which the output of the phase conversion circuit 41 to 1/2 so as to generate a sensor driving signal SE which is delayed by the prescribed time τ3 from the phase of the signal SD. The apparatus is composed of a capacitance-type PWM output sensor 8 by which the signal SD is applied to the input terminal, on one side, of an EXOR circuit 7 through a time constant circuit composed of a resistor R1 and a capacitor C1, by which the signal SE is applied to the input terminal, on the other side, of the EXOR circuit 7 through a time constant circuit composed of a resistor R2 and a capacitor C2 (which is changed differentially with reference to the capacitor C1) and which obtains a PWM(pulse- width mudulation) signal from the output of the EXOR circuit 7. The apparatus comprises a detection circuit 20. In addition, the apparatus is composed of a feedback amplifier 33 which amplifies the output of the detection circuit 20 so as to be fed back to a threshold circuit inside the phase conversion circuit 41 and which controls its threshold. |
