MEMS Microphones: Concept and Design for Mobile Applications

Despite MEMS microphone market getting more mature, the demand is still increasing due to the integration of several units in the same mobile device. Moreover, product specifications are pushing toward contradicting directions—increase of Signal-to-Noise Ratio (SNR) and Acoustic Overload Point (AOP)—with a continuous miniaturization of the package and power savings. To achieve those targets, the development of both the sensor and the readout circuitry must proceed in close interaction to allow trade-offs and define irremovable constraints. The use of behavioral models for the sensor as well as the package allows tailoring the design of the readout electronics to the specific requirements of the acoustical system, leading to the optimum performance in terms of noise and power consumption. After introducing the most commonly used techniques to map the electroacoustical properties of transducer and package, a design example of a state-of-the-art digital microphone system with 140 dB SPL full scale and achieving an SNR of 67 dB at the reference level of 94 dB SPL is presented.