Dissertation Defense, Renfeng Jin

Title: Sub-nanosecond Pulse Characteristics of InGaP/GaAs HBTs


Using a novel sub-nanosecond pulse current-voltage measurement technique, this dissertation shows that InGaP/GaAs HBTs can survive stronger impact ionization and to have a much larger safe operating area (SOA) than previously measured or predicted. The extension of safe operating area is mainly attributed to the elimination of the self-heating effect due to the short conduction time. To interpret this phenomenon quantatively, in this dissertation, avalanche breakdown effect is carefully characterized and an empirical model for impact ionization with voltage and current dependence was extracted and added to a commercially available HBT model. The modified model could accurately predict the HBT characteristics across the enlarged safe operating area. Meanwhile, a new method is developed to forecast the ruggedness of CW Class-C power amplifiers by using measured safe operation boundary.

An ultra-wideband pulse generator was designed with the new model and fabricated in GaAs HBT IC technology. The generator includes delay and differential circuits to generate Gaussian impulse from a TTL input signal, and a Class-C amplifier to boost the pulse amplitude while compressing the pulse width. By adjusting the collector bias of the Class-C amplifier, the pulse amplitude can be varied linearly between 3.5 V and 11.5 V while maintaining the pulse width at 0.3±0.1 ns. Alternatively, by adjusting the base bias of the Class-C amplifier, the pulse width can be varied linearly between 0.25 ns and 0.65 ns while maintaining the pulse amplitude at 10±1 V. Additionally, the amplified impulse signal can be shaped into a monocycle signal by an L-C derivative circuit. These results compare favorably with those of other pulse generators fabricated in CMOS ICs, step-recovery diodes, or other discrete devices.  

Committee members:

Dr. James Hwang

Dr. David R. Decker

Dr. Douglas R. Frey

Dr. Boon S. Ooi

Dr. Walter R. Curtice

Dr. Subrata Halder