Noise Reduction in Transistor Oscillators: Part 1—Resonant Circuits

This series of articles discusses oscillator phase noise reduction techniques and gives specific resonant circuit solutions using lumped and distributed parameters for both frequency stabilization and phase noise reduction. These topics are covered in Part 1. Phase noise improvement can also be achieved by appropriate low-frequency loading and feedback circuitry optimization. The feedback system incorporated into the oscillator bias circuit can provide the significant phase noise reduction over a wide frequency range from the high frequencies up to microwaves. Particular discrete implementations of a bipolar oscillator with collector and emitter noise feedback circuits will be described in Part 2. A filtering technique based on a passive LC filter to lower the phase noise in the differential oscillator will also be presented, with several topologies of fully integrated CMOS voltagecontrolled oscillators using the filtering technique shown and discussed. Part 3 concludes the series, and includes a novel noise-shifting differential VCO based on a single-ended classical three-point circuit configuration with common base, which can improve the phase noise performance by a proper circuit realization. An optimal design technique using an active element based on a tandem connection of a common source FET device and a common base bipolar transistor with optimum coupling of the active element to the resonant circuit is also presented. The phase noise in microwave oscillators can also be reduced using negative resistance compensation increasing the loaded quality factor of the oscillator resonant circuit. Finally, a new approach utilizing a nonlinear feedback loop for phase noise suppression in microwave oscillators is discussed.