A comparative study of lowpass continuous-time delta-sigma modulators with pulse-shaped DACs

Graduation date: 2006Recently, continuous-time ΔΣ modulators are appearing increasingly often in both the literature and the marketplace due to their features of inherent antialiasing and relaxed requirements for opamp and so on. However, several nonideal factors such as clock jitter, excess loop delay, inter-symbol interference and so on, degrade the SNR performance of continuous-time ΔΣ\ud modulators.\ud \ud This thesis first describes how to synthesize a continuous-time delta-sigma\ud modulator with pulse-shaped feedback DAC from an optimal discrete-time noise transfer function, which can be obtained from R. Schreier's Toolbox. Then we analyze theoretically the effects of implicit anti-aliasing filter, excess loop delay and jitter noise, based on the transfer functions of the mixed CT-DT system. Finally, three 4th-order 4b-quantizer CT ΔΣ modulators, with traditionally rectangular, exponentially decaying and sinusoidal decaying feedback DACs are simulated and compared in several aspects such as sensitivity to clock jitter, the effect of DAC mismatch and so on