Wolfspeed, Inc.
Doherty Amplifier Circuit with Integrated Harmonic Termination

Abstract:

In a Doherty amplifier, outputs of first (main) and second (peak) transistors are connected by a combined impedance inverter and harmonic termination circuit. The harmonic termination circuit incorporates a predetermined part of the impedance inverter, and provides a harmonic load impedance at a targeted harmonic frequency (e.g., the second harmonic). Control of the amplitude and phase of the harmonic load impedance facilitates shaping of the drain current and voltage waveforms to maximize gain and efficiency, while maintaining a good load modulation at a fundamental frequency. Particularly for Group III nitride semiconductors, such as GaN, both harmonic control and output impedance matching circuits may be eliminated from the outputs of each transistor. The combined impedance inverter and harmonic termination circuit reduces the amplifier circuit footprint, for high integration and low power consumption.