A transmitter for transmitting a signal comprising: a power amplifier; and a driver amplifier, an output of the driver amplifier being connected to an input of the power amplifier via a first load modulation device comprising a first varactor-based matching network operable to match the impedance of the driver amplifier output with the impedance of the power amplifier input, further comprising a second load modulation device comprising a second varactor-based matching network connected to the output of the power amplifier and operable for matching the impedance of the power amplifier output with a connectable input impedance of a further device; and means for applying envelope tracking to the power amplifier and the driving amplifier; a digital pre-distortion device operable to apply pre-distortion to the signal to compensate for non-linearity of the driver amplifier and the power amplifier and the varactor-based matching networks, wherein the digital pre-distortion device comprises: a first digital pre-distorter connected to the second varactor-based matching network and arranged to provide a control signal thereto, and operable to apply pre-distortion to compensate for non-linearity of the power amplifier and the second matching network, wherein the second varactor-based matching network is arranged to pass a signal reflecting the load modulation at the output of the power amplifier back to the first digital predistorter for the formation of a control feedback loop; and a second pre-distorter being consecutive to the first digital predistorter, connected to the first varactor-based matching network and arranged to provide a control signal thereto, and operable to apply pre-distortion to compensate for non-linearity of the driver amplifier and the first varactor-based matching network, wherein the first varactor-based matching network is arranged to pass a signal reflecting the load modulation at the output of the driver amplifier back to the second digital pre-distorter for the formation of the control feedback loop. a power amplifier; and a driver amplifier, an output of the driver amplifier being connected to an input of the power amplifier via a first load modulation device comprising a first varactor-based matching network operable to match the impedance of the driver amplifier output with the impedance of the power amplifier input, further comprising a second load modulation device comprising a second varactor-based matching network connected to the output of the power amplifier and operable for matching the impedance of the power amplifier output with a connectable input impedance of a further device; and means for applying envelope tracking to the power amplifier and the driving amplifier; a digital pre-distortion device operable to apply pre-distortion to the signal to compensate for non-linearity of the driver amplifier and the power amplifier and the varactor-based matching networks, wherein the digital pre-distortion device comprises: a first digital pre-distorter connected to the second varactor-based matching network and arranged to provide a control signal thereto, and operable to apply pre-distortion to compensate for non-linearity of the power amplifier and the second matching network, wherein the second varactor-based matching network is arranged to pass a signal reflecting the load modulation at the output of the power amplifier back to the first digital predistorter for the formation of a control feedback loop; and a second pre-distorter being consecutive to the first digital predistorter, connected to the first varactor-based matching network and arranged to provide a control signal thereto, and a first digital pre-distorter connected to the second varactor-based matching network and arranged to provide a control signal thereto, and operable to apply pre-distortion to compensate for non-linearity of the power amplifier and the second matching network, wherein the second varactor-based matching network is arranged to pass a signal reflecting the load modulation at the output of the power amplifier back to the first digital predistorter for the formation of a control feedback loop; and a second pre-distorter being consecutive to the first digital predistorter, connected to the first varactor-based matching network and arranged to provide a control signal thereto, and operable to apply pre-distortion to compensate for non-linearity of the driver amplifier and the first varactor-based matching network, wherein the first varactor-based matching network is arranged to pass a signal reflecting the load modulation at the output of the driver amplifier back to the second digital pre-distorter for the formation of the control feedback loop.