Research Of Cmos Mixers

The rapid development of wireless communications market has resulted in a strong drive toward building high level of integration, high performance and low cost RF front-end circuits.As a mature process, CMOS process has the advantage of high level of integration and low cost.With recent advances in fabrication technologies, the cut-off frequency of the transistor has reached hundreds of gigahertz. And more and more attention have been paid on the research of high frequency CMOS RF integrated front-end.The mixer is one of the core modules of RF front-end, the characteristics of which will directly determine the overall performance of the transceiver. This thesis is devoted to the research and analysis of CMOS mixers of24GHz RF front-end. The proposed frontend is composed of two stage down-conversion mixers with the first IF frequency of4.82GHz and the second IF frequency of25MHz.Firstly, the thesis introduces the basic theory of mixer, and expounds the basic principle of mixer, key characteristics and common circuit architectures.Secondly, the most widely used Gilbert mixer is developed in this thesis. This thesis presents the selection methods of the parameters of the transconductance stage transistors and the switching stage transistors through the analysis of the Gilbert mixer circuit model.And then the Gilbert mixer has been designed and simulated for RF applications at the24-GHz band.Thirdly, the optimization method (current bleeding) of CMOS Gilbert mixer is studied in this thesis. The conversion gain of the mixer has been improved nearly10dB by using the method of current bleeding. Then a24GHz CMOS mixers is designed with better performance.Finally, this thesis designed4.82GHz passive double-balanced mixer and active double-balanced mixer. It is shown that the passive double-balanced mixer can be used in the systems which have more emphasis on linearity and low power through the comparison of active mixers and passive mixers.And what reserched in this chapter is very important in reality.