A 125dBSPL 1%-THD, 115μA MEMS Microphone Using Passive Pre-Distortion Technique

CMOS MEMS microphones are widely used due to their superior robustness and easy integration. Single-ended MEMS interfaces are cheaper than the balanced ones, but have an inherent issue with even-order harmonics. This work proposes a passive pre-distortion technique for single-ended microphone interfaces, which leads to significantly lower current consumption, reduction in the ASIC size and module packaging cost while improving total harmonic distortion (THD) and signal-to-noise ratio (SNR) performance. It introduces a programmable technique used to improve the performance of the system by ensuring MEMS nonlinearity compensation at ASIC level exploiting nonlinear capacitance-voltage (CV) characteristics of the AC coupled pMOS capacitor at the input of the read-out circuitry. This simple but effective digitally-assisted analog implementation allows firstly for the sensitivity programming, and secondly for desired trimming of performance parameters such as SNR, acoustic overload point (AOP) and 1% THD level. The proposed work results in 1% THD at 125dBSPL, 66dB system SNR and 10% THD of over 130dBSPL while consuming only 115$\mu$A. This CMOS MEMS microphone based on a single-ended interface achieves the best output-referred figure of merit (FoM) compared versus such state-of-the-art solutions in the smallest possible package. It outperforms other standard solutions in terms of SNR while achieving respectable AOP over 130dB, all with the best-in-class current consumption. The readout IC is fabricated in a standard 0.13um CMOS process.