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A circuit-level methodology for simulating micromachined inertial sensors based on a hierarchical representation of microelectromechanical systems is presented. In the NODAS methodology (NOdal Design of Actuators and Sensors), various surface micromachined suspended microstructures are designed as netlists of general-purpose micromechanical beams, plates, electrostatic gaps, electrostatic comb-drives, joints, and anchors and evaluated using lumped-parameter behavioral models. NODAS provides the user with a one to one correspondence between layout and schematic, and the ability to simultaneously perform circuit level simulation on both the microelectromechanical components and the electronics in the schematic. The on-chip displacements and global position of each micromechanical component are separated in the netlist, enabling application of translation and rotation of the chip while simultaneously providing access to on-chip displacements for position sensing and electrostatic actuation. Each of the components is modeled with an Analog Hardware Description Language. Simulations of static displacements and modal frequencies of a cantilever beam, crab-leg flexure, folded-flexure resonator, capacitive accelerometer, and a vibratory-rate gyroscope are done using an ordinary differential equation solver. Simulation results agree to within 5% of finite-element analysis for displacements with small angles (less than 10°). Simulation of a 16 kHz vibratory-rate gyroscope system with dual transresistance sense amplifiers, a demodulator and a filter illustrates the ability to perform system-level mixed-domain simulation with the NODAS methodology.
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