Abstract — RF circuits exhibit several distinguishing characteristics that make them difficult to simulate

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Multi-standard and multi-band radio are the next milestone in the ever developing radio industry. Frequency agile circuits are an enabling technology which allows us to achieve this goal. It is a low cost and efficient technology that provides the nec-essary flexibility required to implement multi-standard and multi-band radios. One important circuit component which comes easily to one’s mind for frequency tunabil-ity is a varactor; with so many constraints of high tuning range, fast tuning speed and low loss on varactor, new technologies have come up to full fill these require-ments. Among various varactor technologies, Barium Strontium Titanate (BST) has shown promise in the implementation of various tunable circuits like filters, voltage controlled oscillators (VCO), and tunable matching networks with good performance. This thesis concentrates on the use of BST for implementation of frequency agile circuits. Two circuits which form an integral part of any RF transreciever are a VCO and a low noise amplifier(LNA). These circuits were chosen to demonstrate the usability of BST varactor as a tunable element. The VCO implementation shows how a BST varactor can be integrated with modern integrated circuit process like

Analytical methods for the phase-noise analysis of LC-tuned oscillators are presented. The fundamental assumption used in the theoretical model is that an oscillator acts as a largesignal LC-tuned amplifier for purposes of noise analysis. This approach allows us to derive closed-form expressions for the close-tocarrier spectral density of the output noise, and to estimate the phase-noise performance of an oscillator from circuit parameters using hand analysis. The emphasis is on an engineering approach intended to facilitate rapid estimation of oscillator phase noise. Theoretical predictions are compared with results of circuit simulations using a nonlinear phase-noise simulator. The analytical results are in good agreement with simulations for weakly nonlinear oscillators. Complete nonlinear simulations are necessary to accurately predict phase noise in oscillators operating in a strongly nonlinear regime. To confirm the validity of the nonlinear phase-noise models implemented in the simulator, simulation results are compared with measurements of phase noise in a practical Colpitts oscillator, where we find good agreement between simulations and measurements.