| 摘要 |
PURPOSE:To prevent a pressure detecting device from being influenced by a variation of an ambient temperature, and to raise a reliability of a device by connecting a diode to an input part of an impedance converting circuit for processing a detecting signal of a piezoelectric element, and stabilizing an operating voltage. CONSTITUTION:A detecting voltage by a piezoelectric element 11 and also a bias voltage set by voltage dividing resistances R3, R4 are applied through a bias resistance R1 to the gate of an FET17 of an impedance converting circuit 16. A diode 18 is connected to an input part of this circuit 16 in parallel to the resistance R1, and a forward direction resistance value of the diode 18 is smaller enough than a resistance value of the resistance R1 and the element 11, therefore, a device becomes in a state that a potential difference is not generated across the resistance R1. Therefore, even if an ambient temperature is varied, an operating point of the FET17 is not varied, a stable converting output having no temperature characteristic is generated, and a reliability of a pressure detecting device is improved. |
