Progressive RF Power Amplifier With Unequal Split-Combine Paths
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Solution Overview
Problem
Conventional RF power amplifier circuits, such as Doherty amplifiers, face limitations in efficiency at back-off power levels and bandwidth due to the use of quarter wave transformers and direct combining nodes, which restrict efficiency and gain flatness over a range of operating frequencies.
Innovation Solution
A power amplifier circuit with unequal power splitting and combining, featuring parallel amplifier paths with differently biased transistors and phase-matched transmission lines, which allows for increased efficiency and improved gain flatness by isolating amplifier paths and optimizing impedance matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If quarter wave transformers and direct combining nodes are used in conventional Doherty amplifiers, then power combining is achieved, but efficiency and gain flatness are restricted over a range of operating frequencies
Solution Approach 1:
The patent introduces isolation networks as intermediary components between the carrier amplifier and peak amplifier, and between their outputs and the combining node. These isolation networks act as mediators that prevent direct interaction between the amplifiers, allowing each to operate independently across a broader frequency range while maintaining combining functionality. This resolves the contradiction by enabling frequency adaptability without sacrificing efficiency.
Solution Approach 2:
The patent segments the amplifier system into independent carrier and peak amplifier paths, each with its own isolation network. This segmentation allows each amplifier to be optimized for different operating conditions and frequency ranges, improving overall adaptability while maintaining individual efficiency through independent operation.
2Adaptability or versatility
If quarter wave transformers are used in conventional Doherty amplifiers, then impedance transformation is achieved, but bandwidth is restricted
Solution Approach 1:
The patent replaces static quarter wave transformers with dynamic isolation networks that can adapt to different frequency conditions. The isolation networks contain reactive elements that can be tuned or designed to provide effective isolation and impedance matching across a broader frequency range, enabling dynamic adaptation to maintain gain flatness throughout the bandwidth.
Solution Approach 2:
The patent changes the impedance parameters and topological structure from fixed quarter wave transformers to adjustable isolation networks. By modifying the circuit topology to include series and shunt reactive elements, the system can adjust its electrical characteristics across frequency, expanding bandwidth while maintaining gain flatness through proper parameter selection.
3Power
If carrier amplifier and peak amplifier outputs are directly combined, then power amplification is achieved, but load impedance changes when peak amplifier turns on
Solution Approach 1:
The patent introduces isolation networks as intermediary components between the amplifier outputs and the combining node. These isolation networks prevent direct coupling between the carrier and peak amplifiers, so when the peak amplifier turns on, it does not directly change the load impedance seen by the carrier amplifier. This maintains load impedance stability while still achieving power combination through the isolated combining architecture.
Data Source
Figure 1A~1B
Figure 1C~3
Figure 4A~4B
AI summary
A power amplifier circuit (50) includes an unequal power splitter (52) that splits an input signal using an unequal power split and provides a first power level signal and a second power level signal. A first amplifier path includes a first transistor amplifier (53A) that amplifies the first power level signal, and a second amplifier path includes a second transistor amplifier (53B) that amplifies the second power level signal. The second transistor amplifier is configured to turn on at a different power level of the input signal than the first transistor amplifier. An unequal combiner (57) combines the amplified first power level signal and the amplified second power level signal.