Feedback Equilibrium
Closed-loop control circuits generate controllable attractive forces using high-voltage drive signals to hold a micro-electromechanical proof mass at its neutral position. In precision accelerometers and resonant sensors, electrostatic force rebalance counters external inertial displacement by continuously adjusting electrostatic attraction between stationary electrodes and moving elements. This technique extends operational linear range beyond the physical deflection limits of passive mechanical suspensions.
The governing boundary ends where applied actuation voltages exceed the dielectric breakdown threshold of the capacitive gap or trigger mechanical pull-in instability.
Capacitance Modulation
Differential capacitive sense nodes detect minute displacements down to sub-nanometer scales. When micro-scale proof masses move under acceleration, electrostatic force rebalance control loops alter the duty cycle or amplitude of pulse-width modulated pulse streams delivered to opposing forcing electrodes. Non-linear capacitance variations with displacement introduce second-order harmonic distortion unless linearized by differential drive topologies or high-frequency dither.
Voltage Actuation
Precision reference voltages determine the absolute scale factor stability of force-rebalanced instruments. Drift in the analog reference voltage directly scales the closed-loop force output, creating measurement bias.
Bandwidth Extension
Primary calibration relies on tilt-table testing in the earth gravity field or centrifuge testing for high-g ranges. Metrologists verify scale factor linearity by comparing digital feedback duty cycle against reference acceleration values across specified temperature envelopes. Structural damping variations caused by gas pressure shifts within sealed cavity packages alter loop phase margin, requiring precise control of hermetic sealing parameters during manufacturing.
