Integration Design Of Weak Signal Detection Circuit For MEMS Accelerometer

Precision inertial-grade accelerometer systems are highly desired components for a wide range of present-day military and civil applications including the automotive, industrial, consumer, satellite,rocket and missile systems for realizing real time tracking of position. A stable, low-noise, and low-drift interface electronics with high sensitivity is highly desirable component for precision inertial sensors.A fully differential open-loop low-noise interface circuit is implemented for capacitive accelerometer based on the principle of sensors. The front-end circuit reads the sensor capacitance change and produces a voltage signal proportional to capacitance vibration. The switched-capacitor implementation provides parasitic insensitivity and very high signal sensitivity, while allowing monolithic implementation of the interface together with the sensor. To achieve micro-g performance, circuit and system noise sources were analyzed in detail and all the limitations were identified clearly. In this work, we investigate design issues of capacitive position-sensing interface for micromachined inertial sensors, special attentions are paid to noise issues and system modeling issues. Various noise sources in an open-loop sensor are analyzed in detail and some are identified by simulation. A electromechanical interface model with lumped parameters for parasitic capacitances and resistance is developed for interface circuit design. Correlated double sampling (CDS) is used to remove amplifier offset, 1/f, noise, charge injection, clock feedthrough and KT/C noise. The low-noise preamplifier is designed and optimized with a lot of noise restrain methods for reducing parasitic effects especially thermal noise. Since the clock is always active, the minimization of its current consumption is important, and a clock generator basing on source-coupled relaxation oscillator is designed with a frequency of 1.5M. A two-stage core reference voltage structure is introduced for a better precision, in order to reduce charging reference voltage noise. PSRR is as high as 90dB.In this work, the interface circuit for high resolution is operated and simulated by spectre with TSMC 0.18μm technology, power voltage 3.3V.