Abstract: We propose a Sigma-Delta modulator for a GSM system,whose channel bandwidth is wider than 200kHz and dynamic range is more than 80dB.A multi-stage noise shaping structure,rather than a single-loop structure,is chosen to achieve lower OSR and higher stabilization.The design parameters are:fCLK=16MHz,OSR=32,and baseband width=250kHz.Simulation at the circuit level achieves a peak SNDR of 82dB and DR of 87dB.The chip is implemented in SMIC 0.18μm CMOS technology,and the area is 1.2mm×1.8mm.Measurement at 16MHz clock frequency and OSR of 32 achieves a peak SNDR of 75dB and DR over 80dB,which are close to the values obtained by the circuit level simulation.The chip operates under a 1.8V power supply with a power dissipation of 16.7mW.

Key words: Sigma-Delta modulator,  over sampling,  MASH,  dynamic range