Design of VCO for 2.4GHz Wireless Applications Using Transmission Line Resonators R. K. Pokharel, A. Imada, S. Sasaki, H. Kanaya, and K. Yoshida Graduate School of Information Science and Electrical Engineering Kyushu University 744 Motooka, Nishi-ku, Fukuoka, 819-0395 Japan Email: pokharel@ed.kyushu-u.ac.jp Abstract—A voltage-controlled oscillator (VCO) employing on- chip coplanar waveguide (CPW) resonator is proposed for 2.4GHz wireless applications and comparative study between the proposed VCO and a conventional VCO which is composed of LC-tank resonator (LC-VCO), is carried out. By comparing the measured results on the fabricated chip on TSMC 0.35µm BiCMOS technology, it has noted that the VCO employing on- chip CPW resonator is smaller in size by about 30% and frequency-tuning range is higher than LC-VCO. Phase noise is comparable but power consumption is deteriorated. Index terms: VCO, CPW resonator, LC-tank resonator, chip size, frequency-tuning range. I. INTRODUCTION As evidence from the recent and rapid growth of wireless communication systems such as 3G cellular phones, wireless LAN, RFID tags, ETC (ETC: Electronic-Toll Collection) systems and so on, there are ever increasing demands of low cost, high performance, small size, and high speed microwave devices, circuits, components to meet the existing and future demands of wireless systems [1]-[5]. Therefore, the design of high frequency analog circuits (RFIC components) has become important in LSI technology. Although the performance of the CMOS chip has a limitation in the high frequency and high-speed applications, it has become a better option due to its low cost compared to GaAs device [4], [5]. Spiral inductors are indispensable in designing RFIC components such as amplifiers, mixers, voltage-controlled oscillators (VCO), or impedance-matching circuits that results in the miniaturization of RFIC components a difficult task. Distributed elements made of transmission lines to replace spiral inductors are particularly effective when their size becomes smaller, as the frequency in use increases. Among the transmission lines, coplanar waveguide (CPW) is easy to fabricate by the LSI technology compared to its counter part such as microstrip or strip lines because the signal line and ground plane exist on the same plane [6] so that there is no need of via holes. The applications of the distributed elements made of transmission lines were reported in the CMOS or BiCMOS LSI chip [7]-[9]. The CPW was exploited as an inductor and used to design a conventional-type matching circuit for an LNA [7] in microwave frequency band. However, the application of CPW as an inductor takes larger space than a conventional spiral inductor [7]. Some of the present authors have also implemented CPW as a resonator to realize on- chip matching circuits for LSI chip using quarter-wave length resonator and impedance inverters [8], [9]. Furthermore, CPW has also been employed to design VCO at various frequency bands where CPW acts as an inductor [10] and as a resonator [11]. They are particularity effective and popular in millimeter-wave frequency band and above [11]. The on-chip CPW resonator for VCO design in microwave frequency band has not been reported yet to our knowledge. It may be due to its difficulty to accommodate the frequency-dependent resonator’s length for on-chip fabrication. In this paper, we implemented on-chip CPW quarter wavelength resonator to design a VCO for 2.4GHz-band wireless applications on TSMC 0.35 µm BiCMOS technology. The CPW resonators are designed in meander line structure so that it can easily exploit the vacant space of the chip. One of the advantages of the proposed VCO using on-chip CPW resonator compared to a LC-VCO is the chip area which is reduced by about 30%, and higher frequency- tuning range (FTR). Proceedings of Asia-Pacific Microwave Conference 2007 1-4244-0749-4/07/$20.00 @2007 IEEE. 2551