Biography
Enrollment Date: 2008
Graduation Date：2013
Degree：Ph.D.
Defense Date：2013.05.30
Advisors：Zhihua Wang
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：Wireless Power Transfer for Biomedical Applications
Abstract:
In recent years, the dramatic increasing of wireless communication market and great improvement of CMOS process performance promote the development of integrated RF frontend in wireless communication systems, where mixers continue to play a critical role. The existing challenges on mixer design include linearity, noise, and low supply voltage concern. Major issues regarding CMOS integrated mixer design are addressed in this dissertation, focusing on the following three topics: The linearity of high frequency transconductance is an important index in design of mixer, low noise amplifier and some high frequency analog circuits. The traditional way relies on designer’s experience to select circuit parameters to meet linearity requirement, and simulation by a process of trial and error. Effort is made to simplify the design process by finding out the relationship between transconductance linearity index IIP3 (3rd input intercept point) and circuit parameters. In this thesis, Volterra series representation is adopted to analyze the linearity of high frequency transconductance. More detailed MOS transistor model is used than published paper on this aspect. The analytical expression of IIP3 is given. Through applying this expression, the IIP3 value of transconductance can be quickly calculated. Simulated and measured IIP3 are all very close to the calculated result. With the rapid development of VLSI technology and process scaling down, higher integration level demands circuits to be working on lower supply voltage. The most commonly used CMOS mixer topology is the Gilbert mixer. However, its stacked structure limits its usage in low voltage applications. A novel implementation of mixer is presented. The mixer core has only two MOS transistors, which allow it working on a very low supply voltage. Noise and linearity analyses of the mixer are also presented. This mixer is designed in a UMC 0.18 m technology, the measurement result verifies the feasibility of the new design. Normally, to achieve wideband impedance matching during measurement of high frequency integrated mixers, shunt input resistors are added to the mixer’s high frequency input terminals. However, the addition of resistors will introduce extra noise to the mixer so that the measured noise figure is different from the actual value. In order to address this phenomenon, a method to calculate actual noise figure of downconversion mixer with low frequency output based on measured results is developed. An example is given with simulation results to verify the correctness of the method.