Bandpass sigma-delta analog-to-digital conversion

The traditional low-pass sigma-delta (ΣΔ) analog-to-digital converter is extended to the bandpass case. For input signals with small relative bandwidths, bandpass ΣΔ converters offer high signal-to-noise ratios at significantly lower sampling rates than are required for low-pass ΣΔ converters. A sixth-order single-ended switched-capacitor circuit, clocked at 3 MHz, is designed to convert bandpass signals centered at 455 kHz with 20-kHz bandwidth. Time-domain circuit simulations show that this modulator realizes a 94-dB signal-to-noise ratio for a half-scale input, giving roughly 16-b performance