Doherty Power Amplifier Harmonic Injection for Wider Back-Off Range
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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 harmonic components between the main and auxiliary power amplification devices, providing a 180° phase shift and modulating their outputs, thereby enhancing the back-off range without additional power amplification devices.
Engineering Contradictions & Design Principles
Engineering 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
Solution Approach 1:
A harmonic injection circuit is introduced as an intermediary component between the main and auxiliary power amplification devices. This circuit transfers harmonic components (particularly second-harmonic) between the two devices, enabling the auxiliary device to provide load modulation at back-off points without requiring extreme asymmetrical biasing, thereby maintaining linearity while extending back-off range
Solution Approach 2:
The invention changes the operating parameters by injecting harmonic components (frequency parameter change) into the power amplification devices. By transferring second-harmonic components between devices, the system achieves improved linearity at back-off points without sacrificing back-off range extension
2Reliability
If additional power amplification devices are used to amplify harmonic components, then the harmonic injection performance is improved, but the device complexity increases
Solution Approach 1:
The main and auxiliary power amplification devices perform dual functions: they amplify fundamental signals for power output and simultaneously serve as harmonic sources for each other through the harmonic injection circuit. This eliminates the need for separate dedicated harmonic amplification devices, reducing overall system complexity while maintaining harmonic injection performance
Solution Approach 2:
The power amplification devices generate their own harmonic components and exchange them through the harmonic injection circuit. Each device uses the harmonic components from the other to improve its own operation, creating a self-sustaining system that does not require external harmonic generation or additional amplification devices
Data Source
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.