Three-Sub-Amplifier Outphasing Network for Wideband Back-Off Efficiency
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Solution Overview
Problem
Conventional power amplifiers, such as composite power amplifiers, face inefficiencies when handling signals with high Peak-to-Average Ratio (PAR) and may not achieve high efficiency over a sufficiently wide bandwidth, particularly in backed-off operation.
Innovation Solution
A power amplifier design incorporating three sub-amplifiers connected through an output network with asymmetrical transmission line lengths, allowing for multiple frequency regions and partial Chireix-type modes, which enhances efficiency in moderately wide bandwidths and high PAR scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional power amplifiers (class B, AB, F) with fixed RF load resistance and fixed voltage supply are used, then the amplifier operates with simple structure, but the efficiency is low when amplifying signals with high Peak-to-Average Ratio in backed-off operation
Solution Approach 1:
The power amplifier is divided into multiple sub-amplifiers (typically three) with different operating characteristics. Each sub-amplifier handles a specific portion of the output power range, allowing the system to maintain high efficiency across the entire backed-off operation range while keeping individual sub-amplifier structures relatively simple.
Solution Approach 2:
The amplifier transitions from fixed biasing to dynamic biasing where the bias conditions of sub-amplifiers are adjusted based on the instantaneous output power level. This dynamic adaptation allows the amplifier to optimize efficiency at different power levels, particularly improving performance in backed-off operation without requiring complex real-time control circuitry.
2Loss of energy
If Doherty and Chireix type power amplifiers are used to reduce average output current, then the efficiency is improved for amplitude-modulated signals with high PAR, but the bandwidth is limited and efficiency is not maintained over sufficiently wide bandwidth
Solution Approach 1:
The output network employs asymmetrical transmission line lengths connecting the sub-amplifiers to the common output. This asymmetry enables different electrical lengths for different frequency components, allowing the amplifier to maintain high efficiency across a wider bandwidth by optimizing the operating conditions for each frequency region independently.
Solution Approach 2:
The amplifier utilizes changes in electrical length of transmission lines with frequency to adapt the operating characteristics. By carefully designing the asymmetrical transmission line network, the amplifier maintains optimal impedance matching and phase relationships across a wide frequency range, enabling high efficiency over extended bandwidth without requiring multiple amplifiers for different frequency bands.
3Adaptability or versatility
If composite power amplifiers with asymmetrical transmission lines are used to achieve wideband operation, then the bandwidth is increased, but the complexity of the output network increases
Solution Approach 1:
Multiple transmission lines with different electrical lengths are merged into a single common output node. This merging approach allows the network to provide multiple impedance transformation paths simultaneously, achieving wideband operation while consolidating the structure into a manageable configuration rather than requiring separate output networks for different frequency bands.
Data Source
Figure 1~2
Figure 3~4
Figure 5a
AI summary
A power amplifier (100) comprising a first, a second and a third sub-amplifier (111, 112, 113) for amplification of an input signal into an output signal. The sub- amplifiers (111, 112, 113) are connected to an output network (130) for providing the output signal at an output port (140) of the output network (140). The output network (130) comprises a first, a second and a third transmission line (131, 132, 133) connected to the first sub-amplifier (111), the second sub-amplifier (112), and the third sub-amplifier (113), respectively. The first and second sub-amplifiers (111, 112) are operable in a first mode. The second and third sub-amplifiers (112, 113) are operable in a second mode. The first and third sub-amplifiers (111, 113) are operable in a third mode. Each of the first, second and third modes comprises a respective out-phasing mode in a respective part of an amplitude range of the power amplifier (100).