OPTIMAL MEMS PLATE DESIGN AND CONTROL FOR LARGE CHANNEL COUNT OPTICAL SWITCHES

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2004-12-01

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The design and control of an optimal mirror plate actuator suitable for large channel count MEMS optical switch applications is researched. An optimal plate actuator structure is presented. Its performance in equilibrium status is analyzed. A design example, which is confirmed by ANSYS simulation, is given along with a design methodology. By considering the squeeze film damping effects, the transient response of this optimal plate actuator is performed. The system stability is proven by using a Lyapunov function and the Routh-Hurwitz test. A conclusion is that the optimal tilted bottom plate can stably approach the maximum tilt angle with the minimum applied actuating voltage, which is one-half of the present industry standard actuating voltage. A four-level stage structure is given as an example of a practical multi-step realization of such an optimal plate structure. A feedback control system is described using a sensing bridge with a sensing capacitor. Two optimal control methodologies are described, these being fast switching bang-bang control and closed loop feedback control. A high voltage driving circuit is introduced along with design equations based on the special features needed in MEMS mirrors. In addition, by introducing a shift register, a modular architecture to control MEMS mirrors for scalable embedded systems is described. By using this modular structure with its shift register, the system can be scaled when there is a future need to increase channel counts.

Overall, this research improves upon the performance of large channel count MEMS optical switches. It achieves low actuating voltage by reducing by one-half of the present industry standard actuating voltage, that is, a reduction from 250V to 120V. By using the new high voltage driving circuit, it cuts in half the number of required control actuating voltages. It obtains a scalable structure for the embedded system, which is beneficial to cost reduction, future maintainability and design simplification. It provides optimal control to switch the mirrors in order to achieve the minimum switching time and to maintain the stability of the system in the appearance of any perturbation.

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