Design considerations for millimeter-wave power HBTs based on gain performance analysis

On The Operation Configuration of SiGe HBTs Based on Power Gain Analysis

“…After converting the -factor into the -parameter representation and substituting (1)- (4) and (5)- (8) with appropriate approximations, the -factor for the CE and the CB configurations can be derived, respectively, as (30) (31) These two analytical -factor expressions are equivalent to the ones obtained by Tanaka et al [23] when ignoring . It can be easily shown [23] that , indicating that the -factor of the CB configuration increases with frequency at a smaller rate than the CE configuration. Consequently, the frequency point at which the -factor of the CB configuration reaches unity (breakpoint of MSG/MAG) is larger than the corresponding frequency point of the CE configuration , i.e., .…”

“…2(b (30) and (31). It can be roughly approximated as [23] for simplicity) and that of MSG , (15)] need to be compared in order to compare the relative size of MAG and MAG . A straightforward comparison of these two ratios shows that regardless of relative size of and .…”

“…A straightforward comparison of these two ratios shows that regardless of relative size of and . When both MAG and frequency are plotted in logarithmic scale, , in light of the fact that MAG and MAG merge together (with gain value of unity) at the same [23], indicates that MAG must be larger than MAG in the frequency range of . As a result, in the high-frequency range, the CB configuration always offers higher power gain MAG than the CE configuration MAG in spite of the ratio of MSG MSG .…”

“…A preliminary study on the difference of power gain characteristics between the two configurations of AlGaAs-InGaAs HBTs was done by Tanaka et al [23]. In their study, the superior power gain characteristics using the CB configuration for III-V HBTs in a certain frequency range were recognized.…”

Superiority of common-base to common-emitter heterojunction bipolar transistors

“…Consequently, if the extrinsic base resistance ͑thus the total base resistance͒ of an HBT is also made sufficiently small, the power gain superiority of CB configuration can then always be notable. [4][5][6] The major applications of HBTs are high-speed driving and radio-frequency ͑rf͒ power amplification ͑e.g., optical fiber communications and GaAs and SiGe HBTs used in majority of cell phone rf power amplifiers͒. For these applications, large-signal power handling capability of HBTs ͑with associated power gain and power-added efficiency͒ is the most important performance parameter of concern.…”