A new common-emitter hybrid-π small-signal equivalent circuit for bipolar transistors with significant neutral base recombination

• Published in: IEEE transactions on electron devices 1999, Vol.46 (6), p.1166-1173
• Main Authors: Guofu Niu, Cressler, J.D., Gogineni, U., Joseph, A.J.
• Format: Article
• Language: English
• Subjects: Devices; Electric potential; Equivalent circuits; Mathematical models; Operating temperature; Semiconductor devices; Silicon germanides; Voltage
• ISSN: 0018-9383
• DOI: 10.1109/16.766879

The linear superposition approach to the modeling of small-signal parameters in the presence of substantial base recombination, which involves a virtual transistor without base recombination, is identified to cause incorrect emitter current modeling. All of the terminal current changes can be correctly modeled by using the measured forced-V sub(BE) Early voltage in a new equivalent circuit, which properly accounts for NBR and Early effect in a physically consistent manner. As a result, practical situations of small collector-base resistance (r sub( mu )) can be properly handled. r sub( mu ) is related to the ac current-drive and ac voltage-drive Early voltages, which facilitates parameter extraction and circuit modeling. Measurements on state-of-the-art UHV/CVD SiGe HBT's show that the conventional assumption that r sub( mu ) is far larger than the forced-V sub(BE) output resistance r sub(o) does not apply to devices with significant NBR. In practice, r sub( mu ) can be comparable to (and smaller than) r sub(o) depending on the device processing, profiles and operating temperature. Temperature dependent data are presented, and circuit implications are discussed based on the new equivalent circuit.