A 15-bit 140- μ W Scalable-Bandwidth Inverter-Based Δ Σ Modulator for a MEMS Microphone With Digital Output

A discrete-time audio ΔΣ modulator for a MEMS microphone with digital output is presented that features a scalable signal bandwidth to also support ultrasonic frequencies for proximity sensing applications such as gesture recognition. The modulator achieves low power consumption and a small die area by using simple digital inverter instead of OTAs. To increase the robustness of the inverter approach, an LDO is used to provide an internally generated supply which regulates the inverter bias point. The LDO also improves the power supply rejection of the pseudo-differential architecture to above 78 dB. The presented ΔΣ modulator supports a scalable signal bandwidth up to 100 kHz, by dynamically adjusting the internal supply voltage depending on the sampling frequency. In the nominal 20-kHz audio band, it dissipates 140 μW from a minimum 1.5-V supply and achieves a DR of 92.6 dB , a SNDR of 87.9 dB, and a THD of -102.7 dB, respectively.