Title :
An analysis of base bias current effect on SiGe HBTs
Author :
Yo-Sheng Lin ; Shey-Shi Lu
Author_Institution :
Dept. of Electr. Eng., Nat. Chi-Nan Univ., Puli, Taiwan
Abstract :
The anomalous dip in scattering parameter S/sub 11/ of SiGe heterojunction bipolar transistors (HBTs) is explained quantitatively for the first time. Our results show that for SiGe HBTs, the input impedance can be represented by a "shifted" series RC circuit at low frequencies and a "shifted" parallel RC circuit at high frequencies very accurately. The appearance of the anomalous dip of S/sub 11/ in a Smith chart is caused by this inherent ambivalent characteristic of the input impedance. In addition, it is found that under constant collector-emitter voltage (V/sub CE/), an increase of base current (which corresponds to a decrease of base-emitter resistance (r/sub /spl pi//) and an increase of transconductance (g/sub m/)) enhances the anomalous dip, which can be explained by our proposed theory.
Keywords :
Ge-Si alloys; RC circuits; S-parameters; UHF bipolar transistors; heterojunction bipolar transistors; microwave bipolar transistors; millimetre wave bipolar transistors; 0.1 to 50 GHz; SiGe; Smith chart; anomalous dip; base bias current effect; base current; constant collector-emitter voltage; heterojunction bipolar transistors; scattering parameter; shifted parallel RC circuit; shifted series RC circuit; Germanium alloys; Heterojunction bipolar transistors; Microwave bipolar transistors; Millimeter wave bipolar transistors; RC circuits; Scattering parameters; Silicon alloys; UHF bipolar transistors; Anomalous dip; SiGe; base current; heterojunction bipolar transistor (HBT);
Journal_Title :
Electron Devices, IEEE Transactions on
DOI :
10.1109/TED.2004.841347
