| 摘要 |
PURPOSE:To improve the reliability of the detection of the catching of a, foreign matter by generating the detected pressure signal at always constant pressure sensitivity even if the output signal of a pressure sensitive sensor is fluctuated by temperature change, time change and the like or the pressure applying speed is fluctuated in a pressure detecting circuit used in a power window device and the like. CONSTITUTION:A sensor output signal Vout from a pressure sensitive sensor is imparted into a non-inverted input terminal 6a of an operation amplifier 6 through a voltage-controlled attenuator circuit 4 comprising a resistor 2 and a transistor 3. A specified reference voltage Eref is imparted into an inverted input terminal 6b of the operation amplifier 6 from a reference voltage source 7. An output voltage (ea) of the operation amplifier 6 is supplied to the base electrode of a transistor 3 through a time constant circuit 10, a voltage follower 11 and a voltage divider circuit 14. When pressure is applied on the pressure sensitive sensor and the voltage of the sensor output signal Vout is decreased, the voltage change is outputted from an output terminal 5 as the detected pressure signal. |
