Area Efficient High-voltage Charge Pump for Double Backplate MEMS Microphone

Silicon MEMS microphones show competitive advantages to portable consumer electronics with tiny device size, high sound quality, reliability and affordability. The application of MEMS analog/digital microphones can now be found in smart phones, hearing aids, tablets, and automotive voice recognition systems. A double backplate (DB) MEMS transducer brings higher sensitivity and lower distortion compared to a single backplate MEMS. In this paper, we first show an attractive DB MEMS analog microphone where two sufficiently high positive DC voltages are required to bias top and bottom backplates, respectively. As a solution, a fully integrated dual-output high-voltage (HV) positive charge pump is proposed, and the layout area saving is about 40%. To verify the design, an analog readout ASIC is fabricated in a standard 0.18 um CMOS process, and the ASIC includes the proposed HV charge pump, clock generation, and other circuit blocks. In silicon validation, two voltages 12.42 V and 12.40 V with no ripples are generated successfully, and the settling time is well within 5 mS. The two voltages can be perfectly applied to the DB MEMS.