Patent ID: 8253485

Claim:
A power amplifier for amplifying an RF input signal, the power amplifier comprising: an amplifier input for receiving the RF input signal, and an amplifier output for outputting an amplified RF output signal; a series stack of power amplifier devices, each arranged to amplify a signal supplied to an input terminal thereof and to generate an amplified signal across two output terminals thereof, the input terminals of each power amplifier being connected in parallel to the amplifier input for receiving the RF input signal, and the output terminals of the power amplifier devices being connected in series to the amplifier output; and a respective intermediate coupling capacitor connected between the output terminals of each adjacent pair of power amplifier devices in said series stack of power amplifier devices for DC isolation of said power amplifier devices, the output terminals of each power amplifier device being connected to respective DC bias voltage supply lines, and wherein, in respect of at least one of the power amplifier devices, the respective DC bias voltage supply lines to which the output terminals are connected include a switch arrangement capable of disconnecting the DC bias voltage, and the respective DC bias voltage supply line to which the input terminal is connected is itself connected to a variable DC bias voltage supply capable of being controlled to provide a normal DC bias voltage or a high DC bias voltage.