Doherty PA Harmonic Injection for Wider Back-Off Linearity

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Solution Overview

Problem

Conventional Doherty power amplifier circuits face limitations in extending the back-off range while maintaining efficiency and linearity, particularly in modern wireless communication systems with high peak-to-average power ratios, due to asymmetrical drain biasing which leads to poor linearity at the back-off point.

Innovation Solution

A Doherty power amplifier circuit with a harmonic injection circuit that transfers second-harmonic components between the main and auxiliary power amplification devices, providing a 180° phase shift and modulating their outputs to enhance efficiency and linearity, thereby extending the back-off range without additional power amplification.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If asymmetrical drain biased Doherty power amplifier circuits are used to extend the back-off region, then the back-off range is extended, but the linearity at back-off point deteriorates

Engineering Contradiction:

Improveback-off rangeVSAvoidlinearity at back-off point

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The invention converts the harmful effect of asymmetrical drain biasing (which causes poor linearity) into a beneficial effect by intentionally introducing second-harmonic components through the harmonic injection circuit. The asymmetrical biasing that previously degraded linearity is now exploited to generate useful harmonic content that, when injected back, improves both linearity and back-off range simultaneously

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The harmonic injection circuit creates a feedback mechanism where second-harmonic components generated by the main power amplification device are extracted and reinjected into the auxiliary power amplification device, and vice versa. This feedback loop of harmonic components enables continuous optimization of linearity across the back-off range without sacrificing the extended back-off capability

Inventive Principle:

Principle #23Feedback

2Power

If additional power amplification devices are used to amplify harmonic components, then harmonic amplification is improved, but device complexity increases

Engineering Contradiction:

Improveharmonic amplificationVSAvoidcircuit structure

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

The existing main and auxiliary power amplification devices perform dual functions: they amplify fundamental signals for power output and simultaneously generate second-harmonic components for injection into each other. This multi-functionality eliminates the need for separate harmonic amplification devices, maintaining power enhancement while avoiding additional circuit complexity

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The power amplification devices serve themselves by generating the harmonic components they need through their own non-linear operation. The main device generates second-harmonics for the auxiliary device, and the auxiliary device generates second-harmonics for the main device, creating a self-sustaining harmonic injection system without external assistance

Inventive Principle:

Principle #25Self-service

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution achieves a wider back-off range, higher power utilization factor, and improved saturated efficiency by waveform amplitude modulation, suitable for high peak-to-average power ratios in wireless communication systems.

Implementation Method 1

a harmonic injection circuit connected with respective outputs of the main power amplification device and the auxiliary power amplification device, wherein the harmonic injection circuit is arranged to transfer harmonic components generated at the main power amplification device to the auxiliary power amplification device and harmonic components generated at the auxiliary power amplification device to the main power amplification device

Methodology Applied

Scientific EffectHarmonic injection:

Implementation Method 2

for modulating the respective outputs of the main power amplification device and the auxiliary power amplification device

Methodology Applied

Scientific EffectWaveform amplitude modulation: Phase Modulation

Data Source

PatentUS10833634B2Doherty power amplifier circuit

Publication Date: 2020.11.10 CITY UNIVERSITY OF HONG KONG

AI summary

A Doherty power amplifier circuit having a main power amplification device, an auxiliary power amplification device arranged in parallel with the main power amplification device, and a load modulation circuit comprising a harmonic injection circuit connected with respective outputs of the main power amplification device and the auxiliary power amplification device. The harmonic injection circuit is arranged to transfer harmonic components generated at the main power amplification device to the auxiliary power amplification device and harmonic components generated at the auxiliary power amplification device to the main power amplification device, when both the main and auxiliary power amplification devices are operating, for modulating the respective outputs of the main power amplification device and the auxiliary power amplification device.