Investigation Of CMOS Active Mixer Noise And Rf Receiving Front-end Key Technologies

With the rapid growth of wireless communications market and the rapiddevelopment of integrated circuits technologies, integrated circuits technologies for RFfront-end were extensively researched. Designers of RF front-end circuits for theendless pursuit of excellent electrical properties, has also been driving relatedtechnological innovation from time to time. Among them, the direct conversionarchitecture with simple structure, highly integrated level is greatly welcomed by theresearchers, and is considered the most promising to become the leading RF integratedtransceiver architecture in the future. However, the superior performance isaccompanied by technical challenges. Even today, the studies undertaken by theindustry around the DC offset, flicker noise, LO leakage and other key technicalproblems never stop. The mixer is one of the core modules of RF receiving front-end,the time-varying characteristics of whose noise complicates related analysis much. It isfor this reason that the noise analysis of mixers has been a challenging problem in RFintegrated circuits subject. Meanwhile, the existing noise analysis model can noteffectively provide design guidelines for the mixer circuits in current sub-micron andhigh-frequency application scenarios. Based on this, how to develop a noise analysismodel of mixers with broader applicability is particularly urgent.The noise characteristic of CMOS mixers and a number of key technical issues forRF receiving front-end have been studied in the dissertation, and some usefulconclusions and results are obtained, where primarily research and innovation are asfollows:1. A sub-micron CMOS active mixer noise model is proposed: Based on the latestsub-micron physical noise model and I-V model of MOSFETs, the large-signal I-Vequation of the mixer is solved by numerical iteration. And then, the noise transferfunctions of the mixer with channel modulation are derived by small-signal analysis.Finally, a noise analytical model considering secondary effects such as subthresholdconductivity and channel length modulation is obtained. 2. A noise analysis method for CMOS active mixer with the memory effect isproposed: Based on linear periodic time-varying theory, the noise transfer equationsof the mixer including the memory effect have been rigorously derived. Bysmall-signal analysis, the periodic time-varying transfer functions of the mixer areobtained. The noise transform coefficients including tail capacitor memory effectcan be solved numerically, and then a high frequency noise analysis model of themixer is finally captured. These two noise models both are unified analytic modelsincluding thermal noise and flicker noise, and can be applied to the noise designand optimization of the mixer with different intermediate frequency characteristics.Although theoretically the two can be combined, for the simple and intuitivepurposes, they are separately demonstrated.3. A conversion gain model with LO signal offsets for CMOS active mixer isproposed: With the approximation of the small-signal cascode circuit, an analyticdriver stage transconductance including the channel length modulation effect isderived suitable for submicron technology. On this basis, an analytical conversiongain model for the mixer is proposed with the existence of various amplitude andphase imbalance of local oscillator signal.4. A gain-adjustable direct conversion RF receiving front-end with merged low-noiseamplifier and mixer is presented: Low flicker noise and high gain are achieved bydecreasing the bias current of switching pairs; DC offset is improved by bothcommon mode feedback and differential mode feedback, making the IF output levelstable. High IIP2is obtained by the differential circuits' architecture and thesymmetrical layout. The circuit with only two stacked MOSFETs, achieves thetarget of low voltage and low power consumption.