Load-pull assisted cad design of inverted Doherty Amplifier without quarter-wave transformer

This paper presents novel design and architecture for inverted Doherty Amplifier. The key point is the removal of the 50 Ω quarter-wave transformer from peaking path used for impedance inversion in a load modulation circuit of a typical inverted Doherty Amplifier. A coupled line is used as all-pass section providing the desired phase offset to achieve high efficiency performance at back-off. This coupled line thus designed as an all-pass filter section with shaped phase characteristic and a 50 Ω image impedance that can be used directly to optimize the inverted Doherty performance. A prototype has been designed to operate at 2350 MHz for Long term evolution (LTE) application. An improvement of more than 25% in the drain efficiency as compared to the Class-B balanced amplifier at approximately 6-dB back-off is reported with this design.