REFERENCES 1. Z.G. Fan, S. Qiao, J.T. Huangfu, and L.X. Ran, A miniaturized printed dipole antenna with V-shaped ground for 2.45 GHz RFID readers, Prog Electromagn Res 71 (2007), 149–158. 2. R.L. Li, B. Pan, T. Wu, K. Lim, J. Laskar, and M.M. Tentzeris, A broadband printed dipole and a printed array for base station appli- cations, IEEE Antennas and Propagation Society International Symposium, San Diego, CA, (2008) pp. 1–4. 3. Q.Q. He, B.Z. Wang, and J. He, Wideband and dual-band design of a printed dipole antenna, IEEE Antennas Wireless Propag Lett 7 (2008) 1–4. 4. W.S. Chen and S.H. Cheng, Characteristics of a planar dipole antenna with a parasitic element, Antennas and Propagation Soci- ety International Symposium, Charleston, SC, (2009) pp. 1–4. 5. R.P. Ghosh, B. Gupta, and S.K. Chowdhury, Broadband printed dipole antennas with shaped ground plane, IEEE Region 10 Con- ference, (2010) pp. 416–421 6. Y. Wang, B.H. Sun, L.H. Wen, D. Xi, and J.X. Huang, Printed broadband dipole antenna with tapered arms for multi-band appli- cations, IEEE International Symposium on Signals, Systems and Electronics, (2010), pp. 1–3. 7. W.S. Yeoh, K.L. Wong, and W.S.T. Rowe, Miniaturized half-bow- tie printed dipole antenna with an integrated balun, IEEE Asia-Pa- cific Microwave Conference, Hong Kong, China, (2008), pp. 1–4. 8. W.S. Yeoh, K.L. Wong, and W.S.T. Rowe, Wideband miniaturized half bowtie printed dipole antenna with integrated balun for wireless applications, IEEE Trans Antennas Propag 59 (2011), 339–342. 9. R.N. Cai, S. Lin, Y.F. Liu, L.J. Chen, C.T. Yang, and J.X. Wang, A printed trapezoid dipole broadband antenna, IEEE International Conference on Ultra-Wideband, (2010) pp. 1–3. V C 2012 Wiley Periodicals, Inc. A DUAL-RESONANCE CMOS VOLTAGE-CONTROLLED OSCILLATOR WITH ENHANCED PERFORMANCE THROUGH NEW VARACTOR TOPOLOGY Sheng-Lyang Jang, Ching-Lun Cheng, Chia-Wei Chang, and Jhin-Fang Huang Department of Electronic Engineering, National Taiwan University of Science and Technology, 43, Keelung Road, Section 4, Taipei, 106 Taiwan, Republic of China; Corresponding author: m9502216@mail.ntust.edu.tw Received 19 September 2011 ABSTRACT: A new fully integrated, dual-band CMOS voltage controlled oscillator (VCO) is presented. The VCO is composed of a p-core cross-coupled and an n-core cross-coupled Colpitts oscillator with dual-resonance LC tank and was implemented in 90-nm CMOS technology with 1.15 V supply voltage. The circuit allows the VCO to operate at two resonant frequencies with a common LC tank. This VCO is configured with 6.3 and 10 GHz frequency bands with differential outputs. The dual-band VCO operates at 6.11–6.413 GHz and 9.72– 10.24 GHz. The phase noises of the VCO operating at 9.72 and 6.4 GHz are À116.31 dBc/Hz and À122.79 dBc/Hz at 1-MHz offset, respectively, while the VCO draws 4/4.28 mA and 4.6/4.92 mW consumption at high/ low frequency band from a 1.15-V supply. V C 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1590–1593, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26882 Key words: dual-resonance LC resonator; CMOS; dual-band voltage controlled oscillator; varactor topology; phase noise 1. INTRODUCTION Voltage controlled oscillators (VCOs) are an integral part of RF transceivers and fully-integrated dual band VCOs play an impor- tant role in dual-band transceivers as required to provide multi- function services. In general, the frequency tuning of VCO is performed by varying the capacitance or inductance, and con- ventional tuning by varactors does not have a sufficient tuning range because of the limitations of the varactor capacitor ratio (C max /C min ). One solution is to tune the multiband VCO using the band switching method. Two types of switching are used in this method. One is capacitance switching [1, 2] and the other is inductance switching [3–5]. Because MOS switches are used in conventional methods to switch the capacitance or inductance, the tuning range at high frequencies becomes narrow as the parasitic capacitance is increased. In addition, increasing the parasitic resistance reduces the Q-factor of the resonators. Alternately, switched parallel VCOs [6] can be used to form a dual-band VCO, and this VCO has advantage of better VCO performance since each band can be optimized for better per- formance, however this method is not a cost effective solution. Previous study on dual-band CMOS VCO [7] uses a differen- tial cross-coupled Colpitts oscillator with a dual-resonance LC resonator. However, the performance of low-band is not compati- ble with a single-band VCO. In this letter, we propose a new dual-resonance CMOS VCO to achieve the goal of high-perform- ance in both high-band and low-band. The idea is to restructure the varactor configuration, because the AM-PM noise conversion can be reduced through the optimized varactor design. 2. CIRCUIT DESIGN A conventional dual-band differential VCO circuit with dual-res- onance has been discussed in Ref. 7, where a pair of varactor in series with inductor is used. The proposed dual-band differential VCO circuit is shown in Figure 1. It uses a new varactor config- uration for improving VCO phase noise. The cross-coupled pMOSFETs (M p1 , M p2 ) with V TH ¼À0.232 V are used to gen- erate one effective negative resistance given by À2/g mp in low frequency range, where g mp is the transconductance of pMOS- FETs. The nMOSFET M n1 to M n4 with V TH ¼ 0.386 V and the capacitors C X form a transconductance-enhanced Colpitts Figure 1 Schematic of the proposed dual band VCO 1590 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 7, July 2012 DOI 10.1002/mop