Signal amplifier using a doherty amplifier

A signal amplifier comprising:

• a splitter for splitting an input signal into two signals to be transmitted respectively through a first and a second transmission paths;
• a first and a second bias control networks for generating base bias signals corresponding to a power level of the input signal by alternating their operation modes, wherein the power level of the input signal lower than a predetermined threshold level is associated with a low input power drive mode and the power level of the input signal higher than the predetermined threshold level is associated with a high input power drive mode of the control networks;
• a Doherty amplifier including a carrier amplifier for amplifying the signal transmitted through the first transmission path and a peaking amplifier for amplifying the signal transmitted through the second transmission path;
• and
• a Doherty output network for matching and outputting the signals amplified at the carrier amplifier and the peaking amplifier.