Balanced Hybrid Coupler High-Frequency Power Amplifier
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Solution Overview
Problem
Conventional high-frequency power amplifiers, especially those based on the Doherty principle, suffer from low efficiency and narrow bandwidth, which limits their ability to handle signals with high crest factors like OFDM, leading to inefficient operation and increased energy consumption.
Innovation Solution
The design incorporates a balanced hybrid coupler positioned at a low impedance level close to the transistors, eliminating intermediate baluns and using a matching network to transform to the system impedance, thereby achieving a broad bandwidth and suppressing odd harmonics, similar to a push-pull amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional Doherty amplifier is used, then efficiency is improved, but bandwidth is narrow
Solution Approach 1:
The amplifier is divided into a main amplifier path and an auxiliary amplifier path, with the main amplifier handling average power and the auxiliary amplifier handling peak power. This segmentation allows each path to be optimized for its specific function, achieving high efficiency while maintaining broad bandwidth through proper impedance modulation.
Solution Approach 2:
The amplifier employs dynamic impedance modulation where the auxiliary amplifier's output impedance changes with signal level. At low power, the auxiliary amplifier presents a high impedance that modulates the main amplifier's load. At peak power, the auxiliary amplifier becomes active and changes the overall impedance, enabling both efficiency and bandwidth requirements to be met.
2Device complexity
If single-ended amplifier is used, then device complexity is reduced, but harmonic spacing deteriorates
Solution Approach 1:
The patent employs asymmetric impedance modulation in the Doherty configuration where the auxiliary amplifier's impedance changes dynamically. This asymmetric behavior at the impedance transformation point enables the push-pull effect that suppresses even harmonics while maintaining a relatively simple amplifier structure without requiring complex filtering.
Data Source
AI summary
An amplifier according to the principle of load modulation comprises a first push-pull transistor, a second push-pull transistor and a balanced hybrid coupler. The first push-pull transistor is configured as a main amplifier and generates a balanced main-amplifier signal. The second push-pull transistor is configured as an auxiliary amplifier and generates a balanced auxiliary-amplifier signal. Outputs of the first push-pull transistor and of the second push-pull transistor are connected to the balanced hybrid coupler in such a manner that the balanced hybrid coupler combines the main-amplifier signal and the auxiliary amplifier signal according to the principle of load modulation to form a balanced output signal.