ANALYSIS AND DESIGN OF A 4^th ORDER BANDPASS SIGMA DELTA MODULATOR FOR GSM COMMUNICATIONS STANDARD

J.J. Ocampo Hidalgo, A. Garcia Ortiz, L. D. Kabulepa, M. Glesner

Abstract

This work addresses the design of a 4^th order bandpass sigma delta modulator (BPSDM) for IF AD converters suitable for second generation cellular standards such as GSM. The resonator architecture of a BPSDM can be derived from the transfer characteristic of a lowpass modulator by means of mathematical transformations. It can be observed that each transformation results in a different cascade of resonators (COR). Therefore different values of performance metrics like SNR, dynamic range, robustness against circuit non-idealities and SFDR can be expected. Behavioral simulations at the architectural level were carried out to find the COR that best meets the requirements imposed by the GSM communications standard and minimizes requirements of the sub-circuits used in the chosen architecture. A BPSDM was designed and sent to fabrication, using a 0.3 µm, double polysilicon, triple metal, N-well CMOS technology. Simulation results are showing that the proposed prototype reaches a SNR of 85 dB and a sampling rate of 80 MHz.

Keywords

bandpass sigma delta modulators and IF digitization

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IMEKO TC

TC4 - Measurement of Electrical Quantities

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