Design of a Delta-Sigma bandpass demodulator for a Z-axis MEMS vibrational gyroscope

This paper describes the design of a Δ ∑ bandpass demodulator for a Z-axis MEMS vibrational gyroscope. In this MEMS device, a silicon mass is driven through electrostatic actuator so that it has a sinusoidal linear motion, with a controlled speed. Attached to such driving mass, a second mass, free to move in the direction orthogonal to the motion of the first mass, is subjected to a Coriolis force, proportional to the product of the first mass speed by Z-axis rotational speed. The sensing of the Coriolis force and, in turn, of the Z-axis rotational speed, Is performed in closed loop fashion, by measuring the restoring force needed for keeping the sensing mass at the equilibrium position. The restoring force is applied to the sensing mass through a quantized actuation signal, which is obtained from the output bit stream of a band-pass Delta-Sigma converter, containing the information of the Coriolis force. The design of the sensing control loop and simulation results regarding the signal-to-noise ratio achievable with the proposed design is reported. Finally, the issue of the realization of the proposed solution with switched capacitor (SC) technology is also addressed.