Resonant drive: sense and high voltage electrostatic drive using single MEMS capacitor and low voltage electronics

This paper describes the resonant drive technique that eliminates the need for high voltage integrated circuits (IC) in MEMS drive electronics. Resonant drive also offers a versatile solution for position sense and generates the sense signal using a single drive capacitor. Resonant drive uses the fact that the voltage across the capacitor of a series LC tank can be much higher than the input signal driving the tank. The amplification is maximum at resonance and equal to the quality factor (Q). The tank circuit consists of an external inductor and the MEMS drive capacitor. Since the input signal is amplified through the tank, low voltage electronics can fully implement the drive function. As the actuator gap closes, resonance frequency of the tank decreases. This frequency shift is used for measuring the position. Resonant drive has been successfully demonstrated using torsional MEMS mirrors that require 100V for 20 deg-optical rotation. The LC tank (Q of 15) was formed by using a 390μH inductor. All drive and sense circuits were built using only 10V CMOS parts.