Experimental Verification of Role of Ballast Resistors in SiGe Power HBTs

Abstract

To prevent the dramatic degradation of the device performance of SiGe power heterojunction bipolar transistors (HBTs) and maintain the power efficiency, emitter-ballast resistors and base-ballast resistors have been employed in high power bipolar transistors. The microwave performance of emitter-ballast and base-ballast HBTs has been compared and discussed empirically in the previous work. However, it has not been clearly pointed out that which ballasting scheme should be judiciously employed over the entire useful frequency range and under different operation configurations, in order to extract the maximum RF power performance from power devices. This thesis analyzes the role of ballast resistors in SiGe power HBTs theoretically and experimentally. No-ballast resistors, emitter-ballast resistors and base-ballast resistor in both of common-emitter (CE) and common-base (CB) all have been evaluated separately.