Device Noise in Continuous-time Sigma Delta Modulators With Switched-Capacitor Feedback DACs

We analyze in-band thermal noise in continuous-time delta sigma modulators (CTDSMs) with Switched-Capacitor feedback DACs. We show that in such modulators, noise from around multiples of the sampling frequency aliases to in-band frequencies. We give an intuitive understanding of this phenomenon and describe a model that can be used to analyze noise in such modulators. We present the results obtained using state space analysis. Our results compare well with those obtained from a circuit simulator.