Configuration Dependence of SiGe HBT Linearity Characteristics

Linearity characteristics between common-emitter (CE) and common-base (CB) SiGe HBTs are compared at different frequencies, under different bias conditions and at different input/output matching conditions in this paper. It is shown that, without impedance matching at input/output of the devices, the CB configuration exhibits better linearity than the CE configuration under the same input power level and the difference of IMD3 between the two configurations decreases with the increase of operation frequency. However, when both input and output of the devices are impedance-matched for maximum output power P_out , the CE configuration has better linearity than the CB configuration. Furthermore, without varying the input/output matching, the linearity of the two configurations varies with bias in different ways that the linearity of the CE configuration degrades and that of the CB configuration improves as the bias is increased. Under certain impedance and bias conditions, the CB configuration can provide better linearity, besides higher power gain, than the CE configuration