A bandpass sigma-delta demodulator for digital radio

This paper describes a bandpass Sigma-Delta A/D converter for use in digital radio receivers for conversion of the IF signal. The architecture used is efficient in terms of silicon area usage and has improved performance over previous bandpass converters, allowing the IF to be at a higher frequency than the modulator clock rate. A chopping scheme is used to shift signals from the passband to DC and a lowpass modulator running at a decimated clockrate performs the A/D conversion. Simulation results, along with test results from an IC implementation of the converter, are presented to show the operation of the circuit and its use in radio receivers.