A low distortion Doherty amplifier by using tanh function gate bias control

Power amplifiers for communication systems require increasingly high efficiency at large back-off from saturated output power. The Doherty amplifier is one promising solution to solve this problem, however the linearity of the Doherty amplifier is deteriorated compared to class-AB amplifiers. In this work a low distortion Doherty amplifier is proposed, using a tanh function to control the gate bias with changing input signal. Simulations show that ACPR of the biased controlled amplifier is improved by 5dB compared to no control, without significantly affecting the efficiency. Experimental results also show how the amplifier AM-AM characteristic is linearized by the tanh function.