A Low-Power Digital Capacitive MEMS Microphone Based on a Triple-Sampling Delta-Sigma ADC With Embedded Gain

A triple-sampling Delta Sigma ADC can replace the programmable gain amplifier commonly used in the readout circuit for a digital capacitive MEMS microphone. The input voltage can then be multiplied by subtracting a further half-period delayed differential input and using the feedback capacitor of the DAC as a sampling capacitor. This triple-sampling technique results in a readout circuit with noise performance comparable to recent designs, but with a reduced power requirement and increased sensitivity. A MEMS microphone incorporating this readout circuit, fabricated in a 0.18 mu m CMOS process, had an area of 0.98mm(2), achieved an A-weighted SNR of 62.1 dBA at 94 dBSPL with 520 mu A current consumption, to which triple-sampling was shown to contribute 4.5 dBA.