The effects of quantizer metastability on the SNR of continuous-time /spl Sigma//spl Delta/ modulators with return-to-zero switched current DAC

This paper presents a study of the effects of the quantizer metastability in a continuous-time (CT) sigma-delta modulator (SigmaDeltaM). First, the implementation description of a CT SigmaDeltaM with a return-to-zero (RZ) switched-current (SI) DAC is presented. Then, starting with a theoretical description of the quantizer metastability, this non-ideality is analytically studied, modeled and its effect on the overall signal-to-noise ratio (SNR) is discussed. Some measurements on a real chip are done to validate the model accuracy. It is shown that the minimum gain-bandwidth (GBW) product of the practical integrated quantizer required to achieve the maximum SNR is predicted with less than 10% error