A CMOS fully-differential bandpass /spl Sigma//spl Delta/ modulator using switched-current circuits

This paper presents a fourth-order bandpass sigma-delta modulator that has been designed using fully-differential switched-current circuits in a 0.8 /spl mu/m CMOS technology. The modulator prototype has been obtained by applying a lowpass to bandpass transformation (z/sup -1/->-z/sup -2/) to a second-order lowpass /spl Sigma//spl Delta/ modulator. Specifications are SNR/spl ges/60dB@2.5MHz/spl plusmn/15kHz, for a clock frequency of 10 MHz. Preliminary results from the fabricated prototype obtains the correct noise shaping up to 2.5 MHz clock frequency.

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