A Digital Capacitive MEMS Microphone Readout Interface with 60 dB SPL Wake-Up Level SAD for IoT Speech Recognition

This paper presents a low-power digital capacitive MEMS microphone readout interface with an integrated sound activity detector (SAD) for speech recognition in IoT applications. The proposed circuit employs a capacitive differential programmable gain amplifier and an advanced SAD scheme, enabling wake-up at very low sound pressure level (SPL) of 60 dB SPL. The readout is designed with a rapid wake-up time of 0.84 ms and achieves ultra-low standby current consumption of 7.7 μA. Fabricated in a 0.18 μm CMOS process, the implemented system demonstrates a measured A-weighted signal-to-noise ratio (SNR) of 65.4 dBA at 94 dB SPL. The integration of sensitive wake-up detection and high-performance digital readout functionality within a single chip significantly advances the design of low-power MEMS microphones for energy-constrained IoT devices.