METHODS FOR CLOSED LOOP OPERATION OF CAPACITIVE ACCELEROMETERS AND SUCH CAPACITIVE ACCELEROMETERS

摘要

A capacitive accelerometer comprises a proof mass (103), first and second fixed capacitive electrodes (101, 102), and a DC biasing element (704) arranged to apply a DC voltage of magnitude V_B to the proof mass (103) based on a threshold acceleration value. A first closed loop circuit (713) is arranged to detect a signal resulting from displacement of the proof mass (103) and control the pulse width modulation signal generator (700) to apply the first and second drive signals V₁, V₂ with a variable mark:space ratio. A second closed loop circuit (715) is arranged to keep the mark:space ratio constant and to change the magnitude, V_B, of the DC voltage applied to the proof mass (103) by the DC biasing element (704) so as to provide a net electrostatic restoring force on the proof mass for balancing the inertial force of the applied acceleration and maintaining the proof mass at a null position, when the applied acceleration is greater than a threshold acceleration value.