Amplifier circuit and rf transmitter incorporating the circuit

The dc collector or drain current of class B amplifying transistor 101 is detected by a sense resistor 108 and differential amplifier 112. The output voltage Vcc of the switching regulator 107 is controlled to be in proportion to the sensed current so that the amplifier operates slightly below saturation at all input power levels. In a class B amplifier, the DC supply current is proportional to the output RF power level. The amplifier may be used in mobile or base stations. The technique avoids the effect of transistor variations with time or variations between devices. There is no need to calculate the power envelope from in-phase and quadrature data and there is no need to compensate for inherent delays to achieve matching of the supply voltage and the RF power envelope.