An Analysis of Base Bias Current and Intrinsic Base Resistance Effects on InP-InGaAs, InGaP-GaAs, and SiGe Heterojunction Bipolar Transistors

摘要

An analysis of the effects of base bias current (I_B) and small-signal intrinsic base resistance (R_(bin)) on the RF performances of various HBTs, including InP-InGaAs, InGaP-GaAs, and SiGe HBTs, are demonstrated. It was found that for these HBTs, both the real part of the equivalent input impedance [Re(Z_(in))] and the equivalent output impedance [Re(Z_(out))] increase with the increase of R_(bin). Therefore, an increase of R_(bin) (i.e., reducing the base doping, reducing the base width, and increasing the equivalent distance between the emitter-base junction and the base contact) makes the kink phenomena of both the scattering parameters S_(11) and S_(22) of these HBTs more prominent. These phenomena can be explained by our derived analytical expressions of Z_(in) and Z_(out). In addition, for relatively smaller R_(bin), it was found that under constant collector-emitter voltage (V_(CE)), an increase of I_B [which corresponds to a decrease of base-emitter resistance (r_π) and an increase of trans-conductance (g_m)] enhances the anomalous dip. However, for relatively larger R_(bin), it was found that under constant V_(CE), an increase of I_B obscures the anomalous dip. These phenomena can also be explained by our proposed theory.