Layout Synthesis of Accelerometers Master of Science Project Report

Automatic layout generation of a surface-micromachined accelerometer from user-supplied specifications is presented. An accelerometer is an inertial sensor used to measure accelerations. An ADXL76 style accelerometer is chosen as the synthesis topology. The design problem is formulated as a formal non-linearly constrained numerical optimization problem by using the physical dimensions of the device and sense modulation voltage as the design variables. Analytical models for both open-loop and closed-loop control are derived for the accelerometer performance characteristics in terms of the design variables. Constraints which ensure physically valid design and high-level specifications of the accelerometers, such as sensitivity, minimum detectable acceleration and maximum detectable acceleration, are defined by the using these analytical models. Objective functions such as minimize area, minimize noise, minimize a normalized sum of area and noise, and maximize range are used to drive the optimization to different parts of the design space. A generic analog force-feedback loop with phase-leading compensation is used to describe the closed-loop operation of the accelerometer. Layouts are synthesized for different objective functions. Trade-offs among different objective functions are discussed based on the generated layouts. Layouts synthesized for open-loop and closed-loop control are compared. Results show that the force-feedback control can substantially increase the range of the accelerometer.