Unequal Doherty Power Amplifier for Back-Off Efficiency and Flat Gain
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Solution Overview
Problem
Conventional Doherty amplifier circuits face limitations in maintaining near-peak efficiency 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
The proposed power amplifier circuit employs an unequal power splitter and combiner with differently biased transistor amplifiers, allowing for unequal power division and combination, which enhances efficiency at lower output power levels and maintains flat gain characteristics across frequencies by isolating amplifier paths and using phase-different transmission lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If quarter wave transformers and direct combining nodes are used in conventional Doherty amplifier circuits, then power combining is achieved, but efficiency and gain flatness are restricted over a range of operating frequencies
Solution Approach 1:
The amplifier circuit is segmented into multiple independent amplifier paths (first amplifier path with first transistor amplifier, second amplifier path with second transistor amplifier) that are isolated from each other. Each path processes signals independently through separate transmission lines with different phase lengths, avoiding the direct interaction problems of conventional combining nodes while maintaining power combining capability through the combiner at the output stage.
Solution Approach 2:
The patent employs asymmetric design by using transmission lines with different phase lengths (first phase length for first amplifier path, second phase length for second amplifier path) and unequal power splitting ratios. This asymmetric configuration allows each amplifier path to operate optimally at different power levels and frequency ranges, improving overall efficiency and gain flatness across the frequency spectrum.
2Reliability
If amplifiers operate at back-off power levels, then linearity is maintained for multi-carrier communication systems, but DC to RF conversion efficiency decreases
Solution Approach 1:
The patent implements dynamic operation by configuring amplifiers to turn on at different power levels. The first transistor amplifier and second transistor amplifier are biased differently so that as input power varies, different amplifiers become active at different thresholds. This dynamic switching allows the system to maintain linearity at back-off levels while keeping amplifiers operating in high-efficiency regions when active.
Solution Approach 2:
The patent changes operating parameters by using different bias conditions for different amplifier paths and employing transmission lines with different phase lengths. This allows the system to adapt its operating characteristics dynamically, maintaining both linearity and efficiency across varying power levels by adjusting which amplifiers are active and how they are configured.
3Power
If conventional Doherty amplifier circuits use direct combining nodes, then power combination is achieved, but bandwidth and efficiency are limited
Solution Approach 1:
The patent introduces isolated transmission lines with different phase lengths as intermediaries between the amplifiers and the combiner. These transmission lines act as mediators that allow power combination to occur without direct interaction between amplifiers, thereby maintaining bandwidth and efficiency advantages while achieving the necessary power combination capability.
Data Source
AI summary
A power amplifier circuit includes an unequal power splitter 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 that amplifies the first power level signal, and a second amplifier path includes a second transistor amplifier 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 combines the amplified first power level signal and the amplified second power level signal.