Wideband Receivers: Design Challenges, Tradeoffs and State-of-the-Art

A universal wideband receiver supporting multi-band multi-standard wireless communications offers the prospective for cost reduction and flexibility improvement of next-generation handheld devices. Unlike the traditional narrowband receivers that are tailored for specific standards and are assisted by dedicated SAW filters to restrict the input signals (frequency and power), SAW-less wideband receivers are fully exposed to the dynamic spectrum conditions, stimulating circuits and systems innovation to surmount the challenges while keeping up the integration level, power and area efficiencies. This article outlines the design challenges and fundamental tradeoffs of wideband receivers, and describes how they can be addressed by three circuit techniques: noise cancelling, N-path filtering and N-path mixing improving the noise figure, out-of-band linearity and harmonic-rejection capability, respectively. Case studies of silicon-proven solutions representing the state-of-the-art are included, illustrating the pros and cons of different implementation and combination of such three techniques. Architecturally those wideband receivers can be classified as: i) current-mode passive-mixer receiver; ii) voltage-mode passive-mixer receiver; iii) current-mode active-mixer receiver, and iv) current-mode parallel active/passive-mixer receiver. This article should be relevant to junior designers preparing to jump-start in this evolving field, and experience designers intended to collectively compare the existing solutions before further development.