Investigation and Design of Low Phase Noise and Wideband Microwave VCOs

This thesis studied the design techniques of low phase noise and wideband microwave voltage controlled oscillators (VCOs) used for point-to-point radio applications. First, basic oscillator theories as well as different technologies were reviewed. Then two Cband MMIC VCOs were designed in a commercial InGaP HBT foundry process with different topologies, namely the balanced Colpitts and the balanced Clapp. The circuits were simulated with a commercial harmonic balance simulator and the designs were optimized for the best phase noise performance by studying the implication of various design parameters, such as tank quality factors, transistor current density, feedback capacitor ratio and etc. Simulation results show over 10% tuning range for both topologies and a phase noise of -122 dBc/Hz at 100 kHz offset for the balanced Clapp, 10 dB superior to that of the balanced Colpitts, owing to a higher current excitation.