Theoretical Comparison of Direct-Sampling vs. Heterodyne RF Receivers

An intuitive high-level argument is presented suggesting that direct-sampling radio frequency (RF) receivers using Nyquist analog-digital converters can be as power-efficient as analog heterodyne receivers for equal dynamic range specifications, at least at lower RF frequencies well below the ft of the IC process. System planning for direct-sampling receivers is reviewed, highlighting dBFS/Hz as an intrinsic measure of dynamic range, independent of channel and Nyquist bandwidths. Power dissipation versus dynamic range for recently reported heterodyne and direct-sampling receivers is examined and compared.