Influence of output impedance on power added efficiency of Si-bipolar power transistors

The power added efficiency (PAE) of low voltage RF bipolar power transistors for cellular applications, is carefully analyzed experimentally and theoretically. We found that the transistor with low output capacitance operates in "inverse class AB", which facilitates high efficiencies. FE as high as 77% at 1.8 GHz with 3.5 V supply voltage have been obtained.