A Straightforward Approach for Synthesizing Electromechanical Sigma-Delta MEMS Accelerometers

Area of Science:

• Electrical Engineering
• Mechanical Engineering
• Sensor Technology

Background:

• Electromechanical sigma-delta (EM-ΣΔ) converters offer efficient digital interfaces for micro-electromechanical systems (MEMS) accelerometers.
• Synthesizing EM-ΣΔ loops is challenging due to fixed MEMS elements and lack of direct mapping from electrical counterparts, often requiring trial-and-error.

Purpose of the Study:

• To provide a novel perspective for analyzing and designing EM-ΣΔ loops.
• To simplify the design strategy by separately considering signal and quantization noise loops.
• To enhance MEMS accelerometer performance through improved linearity and stability.

Main Methods:

• Detailed analysis of the EM-ΣΔ loop, including signal loop, displacement modulation path, and digital quantization loop.
• Introduction of a discrete-time PID (proportional integral differential) loop compensator.
• Design and fabrication of a fifth-order EM-ΣΔ accelerometer using 0.35 μm CMOS-BCD technology.

Main Results:

• A clear and straightforward design strategy was established by decoupling the signal and quantization noise loops.
• The discrete-time PID compensator enhanced in-band loop gain and suppressed the displacement modulation path.
• The fabricated system demonstrated improved in-band performance, linearity, and stability.

Conclusions:

• The proposed approach significantly simplifies EM-ΣΔ loop synthesis and reduces design effort.
• The new design strategy leads to superior MEMS accelerometer performance.
• Achieved a noise floor of 1 μg/√Hz with a 1 kHz bandwidth and 140 dB dynamic range.