Ballasting resistor optimum for the self-heating effect compensation in RF power HBTs

Base on the thermal-electric feedback network analysis, the thermal stability factor S is presented to express the thermal stability of the device. It is shown that the self-heating effect is compensated completely and the electrical characteristic of device won't shift when S=0. Furthermore, the expression of the minimum ballasting resistance R
_c
of HBT to compensate the self-heating effect is presented taking into account of the temperature dependence of emitter current, the valence-band discontinuity at emitter junction (DeltaE
_V
), the bandgap narrowing due to heavy doping (DeltaE
_g
), additional ballasting resistance in emitter and base (R
_B
and R
_E
). It is found that the higher the temperature T is, the smaller the minimum ballasting resistance R
_C
to compensate the self-heating effect is. The agreement between theory and experiment is shown to be excellent. Because of the reducing of ballasting resistance, RF power HBT will provide higher output power, power gain, and power-added efficiency (PAE) in an amplifier block