Re-configurable Switched Capacitor Sigma-Delta Modulator for MEMS Microphones in Mobiles

This paper presents a reconfigurable discrete-time audio Sigma-Delta modulator implemented in 0.18-µm CMOS technology. The 600 µm × 400 µm core area SD modulator is based on a 2 + 2 MASH architecture, and features several different operating modes in which noise-shaping order, number of output word bits, sampling rate, and bandwidth can be programmed ad hoc. By design, the power consumption is minimized for the selected operating mode. The achieved performance ranges from 99-dB DR with 4th-order noise shaping and full standard audio bandwidth, while consuming 0.97 mW down to 85-dB DR with second order noise shaping over reduced bandwidth for vocal control operation, while consuming 100 µW. The developed device can be used either to read-out different sources (microphones) or to operate in different modes within the same system (i.e. with the same microphone in different scenarios). The trade-off between performance and re-configurability is the key element of this work.