Design of mm-Wave Local Oscillator Building Blocks for Next-Generation Mobile Backhaul

Abstract

Point-to-point wireless links in the E-Band (71-76GHz and 81-86GHz bands) can provide high-data-rate, easily-deployable, cheap and flexible backhaul solutions, important enablers for the mobile network evolution towards 5G. The development of CMOS/BiCMOS integrated transceivers for E-Band backhaul applications can help reducing the cost and footprint of the equipment, but presents design challenges, mostly related to the use of spectrally-efficient high-order modulations, which mandate high linearity and low phase noise. In this dissertation, local-oscillator generation requirements for E-Band backhaul applications are addressed. Phase-noise specifications for the frequency synthesizer are identified, and custom analog building blocks, namely a VCO and a frequency quadrupler, are proposed. The blocks have been designed in 55nm BiCMOS technology,and measurement results on test chips are presented. A noise-scalable multi-core oscillator is proposed as a key block of the frequency synthesizer. It achieves ultra-low phase noise performance, and allows to trade noise and power consumption according to system requirements, a useful feature in E-Band communications. An analytical model describing the effect of mismatches on the multi-core oscillator is also presented. It provides understanding of the robustness of the proposed solution, and useful insights on in-phase coupled oscillator design. Measurement results demonstrate advances over state of the art, primarily in terms of low phase-noise performance, and show how the proposed circuits are suitable as local oscillator building blocks in direct-conversion E-Band backhaul transceivers