A low phase noise, microwave voltage controlled oscillator (VCO) is built to operate between 7.8GHz and 8.7GHz. The circuit is built on Roger RO6002, which has a thickness of 20 mils, and a dielectric constant of 2.94. The loss tangent of the substrate is 0.0009. The active element used is a dual emitter Infineon BFP420 (former Siemens) low noise Bipolar transistor. It is in SOT-343 package, and is used in a common collector configuration. The oscillator circuit contains both coarse and fine tune controls. An active bias circuit is used to power the oscillator. The output is loosely coupled, resulting in better phase noise. To improve the noise performance, the two varactors used in the coarse tune circuit are connected back-to-back. As the coarse tune voltage is changed from -1.0Vdc to -19.0Vdc, the frequency of oscillation changes from 7.8GHz to 8.7GHz. For a fixed coarse tune voltage, the fine tune control varies the oscillation frequency by about 5MHz per volt. The circuit was designed using the small signal scattering parameters (S-parameters) of the transistor provided by the manufacturer. The circuit prototype, including the impedance matching sections, were simulated using Ansoft Ensemble, Serenade, Sonnet, and other simulators.
| Introduction | Measurements | Fundamental Theory | Transistor Selection |
| Terminating Network Design | Load Network Design | Coarse Tune Design |
| DC Bias Circuit Design | Fine Tune Design | Phase Noise |