Some aspects of the design of software defined receivers based on sampling with internal filtering

Dynamic range, bandwidth, reconfigurability, adaptivity, and scale of integration of modern software defined receivers (SDRs) is limited by their analog and mixed-signal portions (AMPs). Implementation of novel sampling with internal antialiasing filtering radically improves these parameters. This sampling accumulates (with a certain weight) signal energy over several sampling intervals for each sample, whereas conventional sampling utilizes only a small fraction of the signal energy. The accumulation of the signal energy reduces the required AMP gain and nonlinear distortions, filters out jitter, and provides flexible internal antialiasing filtering directly at the input of the analog-to-digital converter (A/D). Therefore, the novel sampling enables digitization close to the antenna, radical increase in the dynamic range and attainable bandwidth of the SDRs, as well as major improvement of their adaptivity, reconfigurability, and scale of integration. Methods of the novel sampling realization and ways of its implementation in SDRs are considered in this paper. Comparative analysis of novel sampling circuits (SCs) and conventional track-and-hold amplifiers (THAs) is performed. Theoretical restrictions that should be imposed on weight functions of the SCs are described, and recommendations for their selection are suggested. Challenges of the novel sampling realization are identified and methods of overcoming these challenges are proposed. Ways of the novel sampling implementation in SDRs intended for different applications are discussed.