Impact of bias current and geometry on noise performance of SiGe HBT low noise amplifier

The noise figure of SiGe HBT for low noise amplification is analyzed and its intrinsic minimum noise figure is expressed analytically. Four types of SiGe HBTs with different transistor geometry of emitter stripe width, emitter stripe length and base stripe number were fabricated using a state-of-art SiGe HBT technology. The considerations involved in the judicious choice of biased current and transistor geometry are explored through theory data and measuring results. A conclusion is drawn that an optimum noise figure can be achieved by proper choice of biased current and transistor geometry with longer emitter length and more base stripe number.