High-Order ΣΔ Interface for Micromachined Inertial Sensors

Emerging automotive and consumer applications such as vehicle stability control, GPS backup and many others are generating a growing demand for inertial sensors with an increasing range of functionality including digital interfacing, built-in self-test, calibration and temperature compensation.
Among various techniques for implementing inertial sensor interfaces, Σ∆ modulation provides the benefits of intrinsically linear, two-level force-feedback and analog-to-digital conversion. Analysis of state-of-the-art, second-order Σ∆ inertial sensors, however, shows that the inherent digitization brings a significant resolution penalty, which cannot be eliminated by simply increasing the oversampling ratio. In addition, a tradeoff between resolution and phase compensation forces the feedback loop in second-order systems to operate with reduced phase margin.  
This dissertation presents high-order Σ∆ modulation as a solution to the resolution and phase compensation limitations of existing implementations. The proposed system performs additional electronic filtering in the feedback loop to eliminate the quantization noise overhead and allows for increased phase compensation without degrading the resolution.
As a proof of concept a fourth-order Σ∆ interface was implemented in a standard 0.5μm CMOS process and tested with a gyroscope and accelerometer achieving 1°/sec/√Hz and 150μg/√Hz of resolution, respectively. Comparison between measurement and simulation shows that the contribution of the quantization error to the total noise of the system is negligible.
Publication date: 
May 31, 2004
Publication type: 
Ph.D. Dissertation
Petkov, V. P. (2004). High-order [sigma Delta] Interface for Micromachined Inertial Sensors. United States: University of California, Berkeley.

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