The Inconvenient Truth about Alias Rejection in Continuous Time Delta Sigma Converters

Continuous-time Delta Sigma Modulators (CTDSM) have Implicit Anti-Aliasing - is a commonly heard refrain in the data-converter design community. We show that this is not the case when a switched capacitor (SC) feedback DAC is used, thereby nullifying one of the principal advantages of continuous-time operation. We give an intuitive understanding of this phenomenon, and propose a power efficient circuit technique to improve alias rejection.