| 摘要 |
PURPOSE:To obtain capacitance dynamic quantity sensor which can increase the capacitance between electrodes, is less in error, and has an excellent S/N by providing a dielectric on the surface of at least either one fixed electrode or a mobile electrode. CONSTITUTION:The difference DELTAC between the capacitances between an upper fixed electrode 3a and mobile electrode 2 and between a lower fixed electrode 3b and the electrode 2 is detected by means of a DELTAC detector 91. On the other hand, by applying a pulse voltage across the electrodes 3a and 3b, electrostatic forces are made to act between the fixed electrodes and mobile electrode. The electrostatic forces are proportional to the duty of a pulse voltage generated by a pulse width modulator 92. By changing the duty of the pulse voltage applied across the electrodes 3a and 3b so that the capacitance difference DELTAC can become zero, the work of the electrode 2 is controlled by means of the electrostatic forces acting between the electrodes 3a and 3b and 2. Voltages VE and VE which are inverted from another are respectively applied across the electrodes 3a and 3b. By converting the duty of the pulse voltage into an analog voltage by means of a low-pass filter 93, a prescribed output is obtained. When the capacitances C become larger while such a drive circuit 9 is used, the error of the output signal is reduced and the S/N is improved. |
