A 1.8 V 828 mu W 80 dB digital MEMS microphone

作者：Jawed Syed Arsalan^*; Cattin Davide; Massari Nicola; Gottardi Massimo; Baschirotto Andrea

来源：Analog Integrated Circuits and Signal Processing, 2011, 67(3): 395-405.

DOI：10.1007/s10470-011-9595-8

• MEMS capacitive microphone
• Readout interface
• Low power low noise readout
• Sigma
• Delta modulator

A single-package digital MEMS Capacitive Microphone (MCM) system is presented. The system consists of a MCM, which is wire-bonded with its readout interface ( RI). The MCM sensor is fabricated using a combination of surface and bulk micromachining, employing diaphragm-stiffening to achieve piston-like diaphragm-movement and attaining required sensitivity with a smaller diaphragm-area. The RI is designed in 0.35 lm CMOS and it consists of a preamplifier ( PAMP), a sigma-delta modulator (SDM), integrated biasing and digital control, converting the MCM capacitive variations into a single-bit over-sampled digital bitstream. The PAMP employs a two-terminal bootstrapped source-follower buffer to make the readout insensitive to the MCM parasitics, subsequently feeding a third-order single- loop singlebit modulator running at 2.5 MHz. The electrical measurements of the standalone RI demonstrate 55 dB A-weighted @ 1 Pa SNDR at the analog PAMP output and 80 dB A-weighted dynamic-range at the digital output, which corresponds to a conversion range from 40 to 120 dB SPL. The SNDR for acoustic measurements is 33 dB A-weighted @ 1 Pa, limited by the higher MCM thermal noise floor and reduced sensitivity (-53 dB V @ 1 Pa). The frequency characterization of the system for the complete audio-band demonstrates the effect of the system package towards higher frequencies (> 9 kHz), giving rise to Helmholtz resonance, and reduction in sensitivity for low-frequencies (<400 Hz) because of acoustic short-circuiting inside the MCM due to flow-by slots. The complete system consumes 460 mu A of total current for a 1.8 V single- supply. The total system dimensions are 4.5 x 2 mm(2) ( excluding the package), demonstrating the viability of a low-area, low-power and high dynamic-range implementation of digital MCM.

• 出版日期2011-6