Pulse drive and capacitance measurement circuit for MEMS electrostatic actuators

Abstract

In this paper we present an electronic circuit for position or capacitance estimation of MEMS electrostatic actuators based on a switched capacitor technique. The circuit uses a capacitive divider configuration composed by a fixed capacitor and the variable capacitance of the electrostatic actuator for generating an output signal that is a function of the input voltage and capacitive ratio. The proposed circuit can be used to simultaneously actuate and sense position of an electrostatic MEMS actuator without extra sensing elements. This approach is compatible with the requirements of most analog feedback systems and the circuit topology of pulsed digital oscillators.

An analysis of electrostatically actuated micro vibrating structures incorporating squeezed film damping effect using an electrical equivalent circuit

“…This displacement is converted to a current controlled voltage source (CCVS) denoted as E D . It is well known that displacement (x) and velocity (V) are related by (21) This expression can be realized in an analogous circuit by fixing the displacement as a node voltage and having 1 F capacitor (C V ) across it. The current through the capacitor (I V = C V × dE D dt ) evaluates the velocity.…”

“…It uses Kernel co-solver for the mechanical equation of motion that has been implemented as a 2nd order integrator circuit with feedback loop, and an electrostatic actuator module. A new circuit which is able to continuously measure the capacitance, position or distance between plates of an electrostatic actuator is reported in [21]. Its working principle allows an estimation of the position with only processing two voltage signals, and does not require anchored capacitive sensors or optical measurements to obtain its value.…”

Pulsed Digital Oscillators for Electrostatic MEMS

“…This has the effect of disconnecting the MEMS from V MAX and discharging the capacitors. When R and D are set to zero again, the charge in the capacitive divider is refreshed, thus the leakage phenomena do not compromise the measurement and long-term DC stability can be guaranteed [17], [18]. The purpose of signal H is to prevent the reset pulse to be propagated to the output through the amplification chain.…”

Position, damping and inertia control of parallel-plate electrostatic actuators

“…Some feedback systems require an additional position sensor to obtain its value [8], or use optical methods [11]; however, recent advances show that it is feasible to estimate distance between plates of the electrostatic actuator with only measuring the electric variables of the driving signal [13,14]. Velocity and acceleration can be easily obtained by taking time derivatives of the distance between the plates:…”