An Interface ASIC for an Atmospheric-Pressure MEMS Gyroscope with PLL-Based Phase Adjustment and SC Amplitude Regulation

An interface for a ±400°/s open-loop split-mode MEMS vibratory gyroscope working under atmospheric pressure is present in this paper. Due to the high damping and low mechanical sensitivity of the sensing element, a high polarization voltage of 30V is used to boost the oscillation amplitude of the drive resonator, and a low-noise trans-impedance amplifier (TIA) is designed to reduce the noise contribution of interface. Moreover, the phase regulation of the drive channel is achieved by a phase locking loop (PLL) with 0.1° phase adjustment for sense synchronous demodulation, eliminating the dc error caused by the split-mode phase delay, and a novel switch-capacitor (SC) amplitude regulation scheme is proposed for noise and area reduction. The output of the sense channel is digitized by a 2nd-order Σ-Δ ADC and further processed by a 58th-order FIR filter and 3rd-order temperature compensation. The interface designed in a 0.18-μm 1.8V/5V CMOS process occupies 12.2 mm2 including all the low-voltage (LV) functional blocks. The gyroscope system draws 5.4mA from a 5-V supply, and achieves a noise floor of 0.002/s/√Hz over a 200-Hz bandwidth and a bias instability (BI) of 6.4°/hr without packaging.