A bandpass subsampled delta-sigma modulator for narrowband cellular mobile communications

Radio receivers for digital cellular systems must respect tight constraints in terms of selectivity and dynamic range. Delta-sigma analog-to-digital converters offer a response to the last problem thanks to their high resolution. On the other hand, selectivity is often achieved by filtering the received signal at an intermediate frequency (IF). Limitations of A/D converters impose usually an extra IF conversion of the signal to a lower frequency before being able to properly digitize it. We propose a new delta-sigma converter operating directly on the IF signal allowing the design of simple receivers offering both a high resolution and a good selectivity. Undersampling the IF signal allows reduction of the load of the digital section of the receiver