Interface circuits for capacitive MEMS gyroscopes

Most of the commercially available microelectromechanical system (MEMS) gyroscopes for consumer electronics are based on the vibratory concept [1-3], in which case the rotary rate is detected through the so-called Coriolis effect. The Coriolis effect is intuitively illustrated in Figure 8.1. A plate with an ideal smooth surface is rotating at a rate Ω, with respect to an inertial frame of reference, for example, the Earth, and a particle A starts to move toward point B at t 0 with a constant velocity v, whose direction points from A to B (Figure 8.1a). The plate is referred to as a rotating frame of reference. In the inertial frame of reference, since the surface has no frictions, the particle will move straightly with a constant velocity until it arrives at the other side of the plate at t₀ + Δt (Figure 8.1b). However, observed from point B, which is static in the rotating frame of reference, the trajectory of the particle is curved, as shown in Figure 8.1c, as there is an extra force applied on the particle. This effect is called the Coriolis effect. Consequently, the extra force is called the Coriolis force and the acceleration caused by the Coriolis force is called the Coriolis acceleration. In this chapter, the output signal of an MEMS gyroscope due to the Coriolis effect is generally called the Coriolis signal. Figure 8.1 The trajectories of a moving particle in an inertial frame of reference and a rotating frame of reference: (a) t = t 0; (b) t = t 0 + Δt; and (c) observed from B.