SiGe HBT scaling implications on 1/f noise and oscillator phase noise

An important concern in RF design is oscillator phase noise. Transistor 1/f noise, base resistance thermal noise, and the base and collector current shot noise, as well as inductor thermal noise can all contribute to oscillator phase noise. This work examines the implications of SiGe HBT scaling on 1/f noise and oscillator phase noise using experimental data from SiGe HBTs, featuring 50 and 120 GHz peak f_T. The relevant importance of individual transistor noise sources in determining phase noise is examined. With scaling, the far-off phase noise improves due to overall base resistance reduction, making 1/f noise an increasingly important concern for synthesizer phase noise. We show that once the 1/f noise level is below a certain threshold, further reduction of 1/f noise is not necessary for frequency synthesizers. A method of determining this 1/f noise threshold is developed, and demonstrated for the SiGe HBTs used.