in fig5 the variable voltage controller is changed as soon as possible after the end of the burst plus 10 u03bcs it is delayed by 10 u03bcs because the burst could still be at full power up until this time therefore the variable voltage controller is changed after about 12 u03bcs and the three bias levels are set just before the variable voltage controller is changed in the embodiment shown in fig1 the power amplifier also employs a microprocessor to change the quiescent collector current icq to three class ab bipolar power transistors possibly every gsm burst 577 u03bcs depending on the power amplifier output power gsm basestations use up to 42 db power control on each burst depending mainly on the mobile position the icq is changed to make correction of the transistors 39 self heating effect possible good efficiency obtainable at high powers and nearly constant gain achievable from the transistor at different power levels the actual value of icq follows a curve based on the power dissipated within the transistor and not just compensating for gain expansion this ensures that the correction for transistor self heating works during dynamic burst see below in addition to achieving adequate static flat gain with power backoff fig1 a shows in greater detail the micro controller 39 s interaction with the last three cascaded amplifiers in order to overcome the internal self heating effect.