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1. A Doherty amplifier having an input terminal for receiving an input signal and having an output terminal for providing an amplified signal of the input signal, the Doherty amplifier being supplied by a first supply voltage and a second supply voltage which have opposite polarities in respect to a reference level, the Doherty amplifier further comprising:
a first transistor, having a first control input for receiving a first input signal derived from the input signal, having a first output, and having a first supply input connected to the second supply voltage; a second transistor, having a second control input for receiving a second input signal being derived from the input signal, having a second output, and having a second supply input connected to the second supply voltage, wherein the phase of the first input signal and the phase of the second input signal differ by 90 degrees and a constant current source is connected to the second output of the second transistor and the second supply input of the second transistor; a third transistor, being connected with a third supply input to the first output of the first transistor, and having a third control input connected to the reference level and having a third output for providing a first amplified signal of the first input signal; a fourth transistor, being connected with a fourth supply input to the second output of the second transistor and having a fourth control input connected to the reference level, and having a fourth output for providing a second amplified signal of the second input signal; and a phase shifting element connected between the third output of the third transistor and the fourth output of the fourth transistor for combining the first amplified signal and the second amplified signal in-phase thus forming the output signal of the Doherty amplifier.
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