of vcon which in turn might cause the active bias transistor hbt 2 to operate in the saturation mode and the base current to be greatly increased accordingly a voltage drop in the resistor rb would become increased resulting in a reduction of a base voltage of the active bias transistor hbt 1 and thus ending up with a malfunctioning of the whole bias circuit by considering the operational principle described so far there is illustrated in fig2 a plot defining operating points of a u201c cascade 2 stage power amplifier u201d in two different voltage modes of vcon each of the operating points can be adjusted depending on the number of active bias transistors connected in parallel 0023 fig3 offers a plot of paes versus output power respectively measured when the quiescent current is set at e g 68 ma and 100 ma and a plot of a rate of increment of pae versus output power measured when the quiescent current is set at e g 68 ma and 100 ma with the output power range being from u2212 5 dbm to 25 dbm as an output power is increased from the value of e g u2212 5 dbm the rate of increment of the pae is decreased from the value of 47 the increment rate of the pae comes to have a negative value when the output power is larger than e g.