Sound Activity Monitor Circuit for Low Power Consumption of Always-On Microphone Applications

A novel sound activity monitor (SAM) circuit for low power consumption of always-on microphone applications is presented. To reduce average power consumption, the ultra-low-power SAM is essential and operates a readout integrated circuit (ROIC) in low power mode with silent input or in normal power mode with voice input. A novel SAM with an architecture that does not include an envelope detector is proposed to achieve low power consumption. A new architecture is also proposed to improve MEMS sensitivity by connecting the SAM input to the source follower (SF) output instead of connecting the SAM input to the MEMS port already connected to the SF. In addition, in order to prevent inefficient frequent operation mode conversion, a feature of delaying the transition to the low-power mode after the sound is silenced is implemented. The proposed architecture is designed and verified based on the standard 0.18 mu m CMOS process. The SAM, which consists of two-stage amplifiers (OA, AMP2), comparators, and a logic circuit, consumes a 1 mu A current. The analog path consisting of SF, OA, and AMP2 in low power mode has a maximum amplification gain of 63 dB and a noise of 72 nV(rms)/root Hz at 1 kHz.