A multirate based band-pass sigma-delta modulator

Abstract

A new architecture is proposed for a 4/sup th/ and 6/sup th/-order band-pass sigma-delta (BP-SD) modulators. The signal band at the input of the modulator and the poles of the first resonator are located at the frequency f/sub s//4, where f/sub s/ is the sampling rate. Two high-pass filters operating in a time-interleaved mode replace the second resonator (and the third one in the 6/sup th/-order case). Unlike other modulators using the two-path strategy, in the proposed one, the poles of the high-pass filters are located at the frequency f/sub s//2. The signal band in the input of the second resonator is moved to the center frequency f/sub s//2 by a modulation process that separates the signal into its inphase (I) and quadrature (Q) comparators. A detailed theoretical analysis of the architecture is done in the paper. Owing to the multirate nature of the proposed modulators, simulation results shows an improvement of approximately 12dB in the input dynamic range when compared to conventional modulators of the same order clocked at the same frequency rate.