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In accordance with the trend of one generation of wireless mobile telecommunications technology every decade since the 1980s, the 2020s belong to 5G, the fifth generation. 5G is expected to provide a diverse range of services from enhanced mobile broadband at multigigabit per second, to supporting the massive Internet of Things revolution. While all the generations up to 4G used the frequency spectrum below 3GHz, 5G is expected to support communication on a wide range of spectrum, ranging from low-bands from 0.6-6GHz and mm-wave bands greater than 24GHz. Forecasts of hundreds of billions of connected devices by 2030 mandate the need for circuit-level techniques to mitigate the increasing interference that comes with this proliferating number of devices. To this end, we investigate techniques to make highly linear, interference resilient CMOS radio receiver front ends for three different application thrusts: sub-mW IoT applications, sub-6GHz 5G applications and mm-wave digital beamforming applications.

The need to operate radios connected to the IoT off tiny coil cell batteries has driven the recent research on sub-mW radio receivers. While existing work has focused on improving sensitivity of the receivers in a power efficient manner, there has been little focus on making them interference resilient. In the first part of this dissertation, we demonstrate a 2.4GHz radio receiver with 10x better interference resilience than the state-of-the-art sub-mW radios in the 2.4GHz ISM band, without compromising much on the sensitivity. We present a proof-of-concept integrated circuit in 28nm bulk-CMOS process and present the in-silicon results.

The ever-increasing number of bands with the advent of sub-6GHz 5G calls for high linearity receiver front-ends, with extremely high tolerance for blockers, both in close-in channels and far-out channels. Current solutions in mobile phones involve the use of multiple SAW and FBAR filters for different bands, making them extremely bulky. The re-discovery of N-path filters, with their impedance translational property, provides a path to SAW-less receivers. In the second part of the dissertation, we demonstrate enhanced N-path filter based receivers, achieving 40dB/decade, 60dB/decade and 80dB/decade RF selectivity. Techniques to synthesize higher order driving point impedances, including the first ever known synthesis of a third order driving point impedance, are presented. Coupled with distortion cancellation techniques, record performance is achieved with respect to close-in blocker resilience. Experimental results from three separate integrated circuit prototypes in 28nm bulk CMOS confirm the benefits of our techniques.

Millimeter-wave massive MIMO arrays are expected to be an enabler of 5G. To this end, it is desirable to have digital beam-forming arrays with high spatial flexibility. This calls for highly linear RF front-ends to cope with in-band interferers. In the last part of the dissertation, we present a 10-35GHz passive mixer-first receiver for use in digital beamforming arrays. Circuit techniques are proposed to enhance the linearity of such receivers, both at baseband and the RF mixer switches. Experimental results from an integrated circuit prototype in 28nm bulk CMOS demonstrate record in-band linearity at these frequencies.

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