An amplifier circuit comprises a first amplifier configured to amplify a first input signal. The output of the first amplifier is coupled to an output node via a first transmission line, the first transmission line comprising a first portion having a first characteristic impedance and a first length, and a second portion having a second characteristic impedance and a second length. A second amplifier is configured to amplify a second input signal. The output of the second amplifier is coupled to the output node via a second transmission line, the second transmission line comprising a first portion having a first characteristic impedance and a first length, and a second portion having a second characteristic impedance and a second length. An auxiliary amplifier is configured to amplify a third input signal. The output of the auxiliary amplifier is coupled via an auxiliary transmission line network to a first intersection between the first and second portions of the first transmission line, and to a second intersection between the first and second portions of the second transmission line.