Doherty Amplifier Harmonic Termination for Compact GaN RF Output
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Solution Overview
Problem
Doherty amplifiers face inefficiencies due to the size increase caused by harmonic control circuits, which hinder compact design and high integration in modern wireless communication networks, especially with the advent of 5G networks requiring multiple antennas and high-efficiency power amplifiers.
Innovation Solution
A combined impedance inverter and harmonic termination circuit is used to connect the outputs of the first and second transistors, allowing for control of harmonic load impedance properties to generate harmonic-controlled voltage and current waveforms, eliminating the need for conventional harmonic control and output impedance matching circuits, particularly for GaN transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional harmonic control circuits are added to Doherty amplifiers, then harmonic control capability is improved, but device size and complexity increase
Solution Approach 1:
The patent combines the harmonic control circuit and output impedance matching circuit into a single integrated circuit. The harmonic control circuit includes series and shunt arms that work together with the output matching network, eliminating the need for separate harmonic control components. This merging reduces device complexity while maintaining harmonic control capability through the coordinated operation of series capacitors, shunt inductors, and output matching elements.
2Reliability
If separate harmonic control and output impedance matching circuits are used, then harmonic control performance is improved, but component count and device size increase
Solution Approach 1:
The output impedance matching circuit is designed to serve dual functions: traditional output matching and harmonic control. The series arm includes capacitors that provide both impedance transformation and harmonic suppression, while the shunt arm includes inductors that simultaneously perform matching and harmonic termination. This multi-functionality reduces component count while maintaining harmonic control performance through the universal operation of each circuit element.
3Productivity
If traditional Doherty amplifier configuration is used, then load modulation functionality is maintained, but efficiency is reduced due to power dissipation
Solution Approach 1:
The patent converts harmful harmonic power that would normally be dissipated into useful energy by using the shunt arm inductors to provide low-impedance paths for harmonic frequencies. This redirects harmonic energy away from the power amplifier devices, reducing power dissipation and heat generation. The series arm capacitors simultaneously use this redirected energy to enhance voltage swing and improve overall amplification efficiency, transforming what was previously waste energy into a performance benefit.
Data Source
AI summary
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.