A new high SNR Sigma-Delta Modulator for fractional-N frequency synthesizers

This paper presents a new digital sigma-delta modulator with 16-bit input and a single bit stream output to control a dual modulus divider of a fractional-N frequency synthesizer. The design consists of two stages. The first stage is a second order error feedback sigma-delta modulator that reduces the effective number of the input from 16 to 3 bits and latter stage used as a concentrator to produce a single bit output. The total SNR is more than 100 dB while the complexity and OSR of the design is low compared to the previous works.