Title :
An analysis of the bias dependence of scattering parameters S11 and S22 of SiGe heterojunction bipolar transistors (HBTs)
Author :
Lin, Yo-Sheng ; Liang, Hsiao-Bin ; Lu, Shey-Shi
Author_Institution :
Dept. of Electr. Eng., Nat. Chi-Nan Univ., Puli, Taiwan
Abstract :
The anomalous dip in scattering parameter S11 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. The appearance of the anomalous dip of S11 in a Smith chart is caused by this inherent ambivalent characteristic of the input impedance. It is found that under constant collector-emitter voltage (VCE), an increase of base current (which corresponds to a decrease of rπ and an increase of gm) enhances the anomalous dip. In addition, the anomalous dip in S11 of SiGe HBTs can also be interpreted in terms of poles and zeros.
Keywords :
Ge-Si alloys; RC circuits; S-parameters; elemental semiconductors; equivalent circuits; heterojunction bipolar transistors; poles and zeros; semiconductor device measurement; semiconductor device models; HBT; S11 scattering parameter; S22 scattering parameter anomalous dip; SiGe; Smith chart anomalous dip; base current effects; constant collector-emitter voltage; heterojunction bipolar transistors; input impedance representation; parallel RC circuit; poles and zeros; scattering parameter bias dependence; series RC circuit; Circuit analysis; Frequency; Germanium silicon alloys; Heterojunction bipolar transistors; Impedance; Radiofrequency integrated circuits; Scattering parameters; Senior members; Silicon germanium; Voltage;
Conference_Titel :
Radio Frequency Integrated Circuits (RFIC) Symposium, 2004. Digest of Papers. 2004 IEEE
Print_ISBN :
0-7803-8333-8
DOI :
10.1109/RFIC.2004.1320695
