Bipolar transistor RF power amplifier

Claim 1

A bipolar transistor R.F. power amplifier comprising a bipolar transistor having base and collector electrodes, an input circuit coupled to the base electrode and an output circuit coupled to the collector electrode, an adjustable collector voltage power supply coupled to said collector electrode, means for deriving a characteristic of an input signal in the input circuit, means for deriving the same type of characteristic of an output signal in the output circuit, and comparator means for comparing said corresponding characteristics of the input and output signals and providing a feedback control signal to the collector voltage power supply, wherein the collector voltage power supply is adapted to adjust said collector supply voltage so that the bipolar transistor operates in a mode where gain, phase shift and input impedance are simultaneously linearised, found at the onset of gain saturation in response to variations in input drive level; further comprising means for sensing the magnitude and sign of the amplifier input reflections and means for deriving another control signal in response to the reflections sensed, said another control signal being used to adapt the feedback conditions of the amplifier; and wherein said sensing means comprises a directional coupler connected to the input circuit of the bipolar transistor, the directional coupler having forward and reflected ports which are coupled to respective inputs of a synchronous detector, the output signal from which is used to provide said another control signal.