A comparative study of digital /spl Sigma//spl Delta/ modulators for fractional-N synthesis

This paper investigates the design of digital /spl Sigma//spl Delta/ modulator (SDM) for fractional-N frequency synthesis. The design considerations are presented. Characteristics of digital /spl Sigma//spl Delta/ modulators compared with their analog counterparts are addressed. Simulation results of 4 types of digital SDMs are presented. The pros and cons of each topology are discussed in detail. Design guidelines of digital SDMs for fractional-N synthesizers are given by this comparative study.

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