Modelling, Analysis and Design of RF Mixed-Signal Mixer for Wireless Communications

Abstract: The explosive growth of the market for wirelesscommunications is driving low cost, highly integrated designsand complex RF/analog mixed-signal integrated circuit (RF AMSIC) products. RF transceiver application is one of the mostimportant wireless applications. However, RF front-end ICdesign is often the biggest challenging problem of the overalltransceiver. A mixer is an essential building block of the RFfrond-end and a linear periodic time-varying (LPTV) circuit. Itis becoming a bottleneck for single-chip realizations. Thereare many challenges in RF mixed-signal mixer design, such asLPTV circuit noise analyzing methods, substrate coupling noiseanalysis and high linearity front-end design.The known commercial SPICE tools for linear circuits areincompatible for the LPTV circuit simulation. This thesisproposed a novel noise analysis approach based on wide-sensestationary (WSS) noise modelling. This approach is simple andaccurate. In particular, it can give a more accurate behaviourprediction for an RF mixer in an early design phase. The reasonis that cyclostationary stochastic process is applied to modelintrinsic noises, i.e. thermal noise, shot noise and flickernoise.Design and optimization of RF mixer ICs is anotherchallenge. Noise figure and linearity are two of the mostimportant performance figures. The reason is that RF signal isso small, e.g. the minimum received signal level at the antennais -102dBm, and that the overall performance of wirelesscommunication system mainly depends on the performance of thefront-end. Thus, it is essential to design a low noise and highlinearity front-end. There are many ways to reach this target,like employing optimum circuit topology, high cut-off frequencytechnology, etc. In this thesis, through a comprehensiveinvestigation, the optimum principle of designing RF mixer ICsis given. By this principle, the mixers were designed using twodifferent technologies, Si and SiGe, at the frequency rangefrom 5GHz to 6GHz.Substrate coupling issues give rise to a critical problem inRF AMS IC design associated with systems on a single chip(SoC). For an RF AMS IC designer, it is preferable to know howmany effects there are from substrate coupling before layoutphase. Considering this requirement, this thesis concentratedon the study about macro-modelling of the substrate couplingnoise in RF AMS IC. The macro-modelling approach is simple andpractical although the modelling is taken by someapproximations. The case studies exhibited that macro-modellingis efficient enough for analysing the substrate couplingeffects. Key Words: LPTV,RF/Analog mixed-signal IC, front-end,RF downconversion mixer, substrate coupling noise.

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