A Digital Capacitive MEMS Microphone for Speech Recognition With Fast Wake-Up Feature Using a Sound Activity Detector

Abstract

This brief presents a digital capacitive MEMS microphone for speech recognition with fast wake-up feature using a sound activity detector. The proposed microphone wakes up only when an acoustic event within the voice-band occurs using the sound activity detector, which can significantly reduce the average current consumption. All wake-up processes are performed on-chip, which enables the fast wake-up feature to prevent missing keywords. In addition, the proposed deglitching technique is applied to prevent the sound activity detector from responding to non-acoustic signals such as glitch signals. An auxiliary low-dropout regulator is used to further reduce the wake-up time. Our microphone consumes only 16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{A}$ </tex-math></inline-formula> in deep-sleep mode. In active mode, a high-performance readout circuit converts the voice signal into a digital signal. The proposed microphone achieves an A-weighted signal-to-noise ratio (SNR) of 62.8 dBA and an acoustic overload point of 119.4 dB sound pressure level. The readout circuit itself of our microphone, fabricated in a 0.18 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process, has an A-weighted SNR of 65.8 dBA.