Active-pasisve delta-sigma modulator ADC for MEMS accelecrometers

This paper presents the modeling of power-efficient active-passive delta-sigma modulator analog-to-digital converter (ADC) for microelectromechanical systems (MEMS) based accelerometer. Power reduction is required for power hungry ADC for MEMS applications due to limited battery life of portable systems. A second-order single-bit cascaded integrator with distributed feedback (CIFB) delta-sigma modulator ADC is investigated in this work to meet the challenges. The signal transfer function (STF) and noise transfer function (NTF) of the modulator discussed for poles and zeroes. The single-bit modulator modeling and simulation results are provided to verify the achieved performance. NTF zero optimization technique is implemented to reduce in-band quantization noise by shaping noise at high frequency. Operational amplifier (op-amp) for the front-end integrator optimized for minimum power consumption by considering non-ideal effect like low finite DC-gain, limited slew-rate, minimum required gain-bandwidth (GBW), the proposed model simulation results are provided and discussed. Non-ideal effect of the proposed overall active-passive CIFB ADC structure for Switched-Capacitor circuit level implementation performed and non-ideal effect like thermal noise, op-amp noise, and switch non-linearity will be discussed for CIFB. Simulation results for the proposed active-passive structure with single-bit quantizer, shows that it can achieve signal-to-noise ratio (SNR) of 90dB for MEMS sensor system bandwidth of 1 kHz with OSR = 520.