# PA linearizing bias circuit？

#### coolsummer

##### Junior Member level 1
Hi, friends, I am a newbie and I’m reading a paper about power amplifier linearizing circuit, the schematic diagram is shown below. The paper says“ The linearizing shunt capacitor with the base–emitter diode of the transistor (HBT2) compensates the decreased base bias voltage of the RF amplifier (HBT1) caused by the increased input power level". I just don't understand why the bias voltage of HBT1 and the base-emitter voltage of HBT2 would decrease if the input power level increases, could anybody help me and explain the linearizing principle of the circuit？

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#### BigBoss

I believe it's a temperature Feedback circuit,While Output Power is increasing, the Package/Junction Temperature increases and if the Transistors Q1 and Q2 are tied to HBT1, Current Control Circuit diminishes the Base Current due to $-2.5mV/C^o V_{BE}$ relation.