All-digital MEMS gyro-sensor using TAD-digital-synchronous-detection (TAD-DSD) By TAD-ADPLL

As sensor digitization for IoT-applications, this paper presents an all-digital MEMS gyro-sensor circuit method, using TAD (Time-A/D converter)-based digital synchronous detection (TAD-DSD) by applying entirely all-digital time-domain processing, which uses no conventional methods such as analogmixers, -filters and -ADCs. The proposed method involves twostep processing: 1) voltage-signal levels of the first-half and lasthalf of one-cycle carrier-waveform are averaged and digitized simultaneously with 0.18μm TAD's moving-average effect using a sampling clock frequency fs twice higher than carrier-wave frequency fcar, then 2) the difference between the first-half and last-half of the digitized carrier-wave voltage levels is calculated to obtain the information of actual carrier-wave amplitude, which indicates angular-rate information from a vibrating MEMS element. In this method, a TAD-sampling clock is generated with a TAD-based all-digital PLL (TAD-ADPLL) to drive the MEMS element. By using a conventional piezoelectric MEMS tuning-fork element, we experimentally confirmed its sensitivity of 0.14(°/s)/LSB and peak noises of ±0.18°/s at BW = 10Hz, achieving a digital-type gyro-sensor for CMOS scaling.