Design Of RF CMOS VCO For 3G Application

Recently, the explosive growth in wireless communications and CMOS process technology have driven universities and companies to produce wireless transceivers at low-cost, low-power, and make on-chip implementation of fully integrated wireless transceiver possible. Nowadays most of modules in transceiver system such as low-noise amplifier (LNA), mixer, IF Filters, power amplifier (PA), and voltage-controlled oscillator (VCO), can be integrated in CMOS scaled technology.In this paper, a voltage-controlled oscillator (VCO) module is analyzed and designed, which can be used for the third generation mobile communications. Firstly, based on analyzing the theory and mathematic model of LC VCO, an implementation of narrowband circuit structure and quadrature-output LC-VCO is proposed Secondly, the structure, lumped circuit model of on-chip spiral inductors and the implementation of on-chip varactors are analyzed. Monolithic transformers having a higher quality factor and accumulation NMOS varactors having a larger capacitor coefficient ratio are employed to implement the circuit. In addition, a very vital parameter for voltage-controlled oscillators—phase noise is studied. According to the phase noise theory, some techniques being necessary to improve the structure of the circuit are attempted to reduce the phase noise. In the end, after optimizing each of the parameters of LC-VCO, a complementary cross-coupled LC-VCO circuit with quadrature outputs is designed. The VCO circuit applies to the third generation mobile communications. Then the circuit is simulated with Spectre RF in TSMC 0.25μm RF/Mixed CMOS process, and the layout of the related circuit is portrayed by means of the Virtuoso Layout Editor.