The Delta-Sigma Modulator of Fractional-N Frequency Synthesizer for Wireless Sensors Network Applications

This paper presents a design of fractional-N frequency synthesizer with low dithering, which is fabricated in a 130nm CMOS process. A 3rd-order delta-sigma modulator is based on digital multi-stage noise shaping (MASH) structure with its second and third stage dithered by 7-bit linear feedback shift register (LFSR) was designed for the frequency synthesizer, and a long word is used for the first modulator in the MASH structure. The simulation result of the whole frequency synthesizer shows that it can output two-way I/Q signal between 2.28GHz and 2.53GHz, and its spurs are lower than-75dBc.