A Wideband High-efficiency Doherty Power Amplifier for LTE

This article describes a broadband Doherty power amplifier designed with a class AB and class C PA that is suitable for LTE Band-7 and Wi-Fi applications. The output matching network is theoretically analyzed, with emphasis on the effect of the auxiliary amplifier’s non-ideal infinite output impedance on parasitic devices. A novel Doherty-like power amplifier (DPA) is constructed with 25 W, 2.2-2.8 GHz GaN HEMT transistors. The quarter-wave transformer that was previously used in the DPA topology was replaced by the corresponding Klopfenstein tapper network. Real-world prototype implementations have shown that this modification increases the achieved DPA bandwidth (BW) compared to conventional topologies while maintaining efficiency values. (Fractional bandwidth equals 24%) The DPA assumes an OBO value of 6 dB, which is typical for basic designs and explanations because the voltage level involved is 1:4 and the peak power amplifier is activated at half of the input voltage’s dynamic range. However, in order to increase the OBO value, the signal must first be compatible with the PAPR value. This can be accomplished by adjusting the power divider in an asymmetrical manner. The OPBO range was extended using the asymmetric DPA technique.