A Chopper Negative-R Delta-Sigma ADC for Audio MEMS Sensors

This paper presents a proposed low-noise and high-sensitivity Internet of Thing (IoT) system based on an M&NEMS microphone. The IoT device consists of an M&NEMS resistive accelerometer associated with an electronic readout circuit, which is a silicon nanowire and a Continuous-Time (CT) ∆∑ ADC. The first integrator of the ∆∑ ADC is based on a positive feedback DC-gain enhancement two-stage amplifier due to its high linearity and low-noise operations. To mitigate both the offset and 1/f noise, a suggested delay-time chopper negative-R stabilization technique is applied around the first integrator. A 65-nm CMOS process implements the CT ∆∑ ADC. The supply voltage of the CMOS circuit is 1.2-V while 0.96-mW is the power consumption and 0.1-mm² is the silicon area. The M&NEMS microphone and ∆∑ ADC complete circuit are fabricated and measured. Over a working frequency bandwidth of 20-kHz, the measurement results of the proposed IoT system reach a signal to noise ratio (SNR) of 102.8-dB. Moreover, it has a measured dynamic range (DR) of 108-dB and a measured signal to noise and distortion ratio (SNDR) of 101.3-dB.