A bandpass sigma-delta demodulator

A new architecture for bandpass sigma-delta A/D conversion/demodulation with particular application in radio reception is described. The proposed architecture is efficient in terms of silicon area usage and has improved performance over existing topologies. A chopping scheme shifts signals from the passband to DC and a lowpass modulator is then used to perform the conversion. In the new implementation, the passband location is limited only by the maximum sampling rate achievable rather than the lower maximum modulator clock rate. Hence, the new converter can digitize bands at much higher frequencies than previous implementations, while an intrinsic anti-aliasing filter means that external anti-aliasing filter requirements are relaxed compared with undersampling converters. Simulation results are presented showing the operation of the converter with a QPSK-modulated input