Patent ID: 9088248
Filing Date: 2015-07-21
Classification: H03F

Abstract:
1. An amplifier comprising: an amplifier input for receiving an input signal; an amplifier output for providing an output signal; a first lower active sub cell and a second lower active sub cell, each comprising an input terminal and an output terminal, wherein the input terminals of the lower active sub cells are connected to the amplifier input and the output terminals of the lower active sub cells are not shorted; a first upper active sub cell and a second upper active sub cell, each comprising a biasing terminal, an input terminal and an output terminal, wherein the input terminals and the output terminals of the upper active sub cells are coupled between the output terminals of the lower active sub cells and the amplifier output; a bias controller configured to provide a first biasing signal to the biasing terminal of the first upper active sub cell and a second biasing signal to the biasing terminal of the second upper active sub cell in dependence on an output power of the output signal; and a coupling impedance which is connected between the output terminals of the lower active sub cells.