Study And Design Of Voltage Controlled Oscillator Based On GaAs HBT

In recent years, the rapid development of wireless communication greatly stimulated the research of low cost, high performance and miniaturization RFIC(Radio Frequency Integrated Circuit). As a key module of RFIC, VCO(Voltage controlled oscillator) has been widely used in wireless receiving, wired receiving, data communication, and clock recovery systems, even in aerospace and medical science. Hence, great attention has been paid to the research and design of VCO. The development direction of VCO is high frequency, wide tuning range and low phase noise because of the shortage of frequency resources and the improvement of wireless transceiver performance Therefore, In this paper, we focus on the improvement of frequency tuning range and the reduction of phase noise. At last, one cross-coupled VCO and one push-push VCO have been successfully designed. The author’s major contributions are outlined as follows:1. The phase noise of VCO has been studied. A detail analysis about the phase noise of voltage controlled oscillator is made and two kinds of phase noise model are introduced. According to the analysis some methods are put forward to reduce the phase noise of the voltage controlled oscillator.2. The differential cross-coupled VCO has been analyzed. The 1-μm Ga As HBT process provided by WIN Semiconductors is introduced in the view of material, device and technology. Ga As HBT process is the very first choice for wide tuning range and low phase noise VCO design due to its high cutoff frequency, strong driven capacity and low flicker noise(1/f). A detail analysis about the structure of the proposed VCO is made based on the principle of negative resistance oscillator. The cross-coupled structure is the most preferred topology in RFIC implementations due to its simplicity, high loop gain, differential operation, robust start-up, and low common-node noise.3. The proposed cross-coupled VCO has been designed and simulated. The wide tuning range is achieved by employing a varactor array Ctune consists of several BC diodes which have the biggest Cmax/Cmin value. The phase noise performance is optimizedthrough process, circuit configuration and parameter values. Simulation and layout design are completed with simulation software ADS and Cadence respectively. The simulation result shows that, with VCC of 6V,the tuning range of the proposed VCO is 1.89GHz(22 to 23.89 GHz), the phase noise is-104.674 d Bc/Hz@1MHz, the Fo M is-176.5d Bc/Hz, and the layout size is 0.7mm×0.7mm. The proposed VCO has superior phase noise performance and wider frequency tuning range comparing with the other reported results.4. The push-push VCO has been studied and designed. The structure of push-push VCO is proposed based on the cross-coupled VCO and the principle of push-push. The analysis about the generation mechanism of the 2nd harmonics is made. The generation of the 2nd harmonics is accounted for by the nonlinear current-voltage characteristic of the emitter-base junction diode causing: 1) significant voltage clipping and 2) different rising and falling time during the switching operation of core transistors. The schematic simulation, layout design, and post simulation are completed using ADS and Cadence. The simulation result shows that the tuning range of the push-push VCO is 14.26GHz~14.89 GHz, the output frequency is 28.52GHz~29.77 GHz, the phase noise is-112 d Bc/Hz@1MHz. It demonstrates that the phase noise performance of the proposed VCO is good, and it realizes the function of push-push successfully. It is a pity that we could not do the tape out and test verification due to time constraints.