Analyze and Design 10-GHz O.8-VDD -117dBcIHz Quadrature LC-VCO in 120nm CMOS Technology Bangli Liang, D. Chen, H. Guo, B. Wang, T. Kwasniewski Depatment of Electronics Zhigong Wang Institute of RF-&OE-ICs Southeast University Carleton University 1125 Colonel By Drive 2 Si-Pai-Lou Ottawa, ON, K1S 5B6 Canada Email:bliang.ddchen.hguoh1.bwang.tak@doe.carleton.ca. Nanjing, Jiangsu, 210096, China Email:zgwang@seu.edu.cn Abstract-A low supply voltage low phase noise 10-GHz CMOS quadrature LC-VCO (LC-QVCO) is systematically an alyzed and designed for low power applications in wireline and wireless communication systems. Using a semi-empirical model, the impacts on VCO oscillation magnitude, loaded quality factor (Qloaded), and oscillation frequency from the parasitic components of passive and active devices are formulated in simple mathematic equations. The predicted VCO performance and the widely used linear model of LC-QVCO are verifed by time domain simulations, frequency-domain total loop gain analysis, and measurement data based on a 120nm RF CMOS technology. I. INTRODUCTION Quadrature clock generation fnds applications in many communication systems. For RF front-ends, quadrature phase is required for image rejection receivers and for downcon verting RFIIF signals to baseband. For high speed clock-and data recovery (CDR) systems, quadrature phase is required for half-rate phase detection, phase-interpolation, and fequency detection. In this decade, a few quadrature LC-VCOs have been designed and implemented [1]-[4] for higher fequencies, higher levels of integration, low power consumption and low costs applications. Predominantly piecewise linear models are used which are based on heuristic methods. For the calculation of the ampli tude the method of describing function is common practice, where typically higher-order hamonics are discarded. In order to guaantee a steady state oscillation the Barkhausen criterion is well-established which is also based on a linearized model of the oscillatory circuit [5]. A comprehensive analysis of quadrature oscillator based on injection locking was addressed in [6], which was validated by a low oscillation frequency (2GHz) LC-QVCO. The models mentioned above provide deep insights into the behavior of fully integrated LC-tank oscillators, however, we still need to fgure out the exact relationship between the VCO performance and device parameters to simplify the design and optimization procedure of high frequency quadrature LC VCOs. Additionally, the widely used linear model based on some assumptions and approximations which are usually valid for lower frequency (below 5GHz) or narrow tuning range 978-1-4244-6878-2/10/$26.00 ©2010 IEEE 420 (a) Tank-1 i ,............................ �.. l .. (b) Fig. 1: LC-QVCO: (a) Schematic, (b) Linear model (M Hz) LC-VCO should be verifed for high frequency (;: lOGHz) and wide tuning range (GHz) LC-VCO since the higher order nonlinearities will play considerable roles at high oscillation fequency. In this paper, a semi-empirical model is used to accurately analyze the impacts on the output magnitude, Qloaded, and oscillation frequency of the proposed l O-GHz quadrature LC VCO fom both passive and active devices. The validity and accuracy of the widely used linear mode of QVCO are verifed by time-domain simulations, fequency-domain total loop gain analysis, and the measured data of the low supply voltage LC QVCO using a 120nm RF CMOS technology.