Doherty Power Amplifier Voltage Combining for Back-Off Efficiency
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Solution Overview
Problem
Doherty power amplifiers face challenges in achieving efficient power amplification, especially at back-off power regions, due to complex designs and amplitude and phase imbalances in current-combining approaches, which affect efficiency and linearity in wireless communication systems.
Innovation Solution
A Doherty power amplifier with a carrier and peaking amplification path, each including a transformer, and a quarter-wave circuit combiner that dynamically adjusts load impedance, allowing for efficient voltage combining and improved power-added efficiency by maintaining high voltage swings and optimizing load impedance matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If current-combining approaches are used in Doherty power amplifiers, then power amplification can be achieved, but amplitude and phase imbalances occur which reduce efficiency and linearity
Solution Approach 1:
The patent inverts the conventional current-combining approach by using voltage combining instead. The carrier and peaking amplification paths are combined through voltage addition at the output node, which eliminates the amplitude and phase imbalance issues inherent in current-combining methods while maintaining power amplification capability
Solution Approach 2:
The patent changes the combining parameter from current to voltage. By transforming the combination method from current-based to voltage-based, the system achieves better efficiency and linearity while maintaining the Doherty architecture's power amplification function
2Manufacturing precision
If complex quarter-wavelength transformation circuits are used, then impedance matching can be achieved, but design complexity increases
Solution Approach 1:
The patent extracts and removes the complex quarter-wavelength transformation circuits from the design. By eliminating these complex impedance transformation networks, the design complexity is reduced while the impedance matching function is simplified through direct voltage combining at the output node
Solution Approach 2:
The output combining node serves multiple functions simultaneously: it acts as both the voltage combining point and the impedance matching point. This multi-functionality eliminates the need for separate quarter-wavelength transformation circuits, simplifying the overall design
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances power-added efficiency by 10% at 26 dBm output power compared to conventional Class AB amplifiers, improving back-off efficiency and linearity, while simplifying the design by avoiding complex quarter-wavelength transformation circuits.
Implementation Method 1
The combiner includes a quarter-wave circuit implemented between the carrier and peaking transformers
Implementation Method 2
Each of the carrier and peaking transformers can include a primary loop and a secondary loop
Data Source
AI summary
A power amplifier can include a carrier amplifier having first and second differential amplification cells with outputs coupled by a primary loop of a carrier transformer, and a peaking amplifier having first and second differential amplification cells with outputs coupled by a primary loop of a peaking transformer. The power amplifier can further include a combiner having a quarter-wave circuit implemented between the secondary loop of the carrier transformer and a secondary loop of the peaking transformer. The quarter-wave circuit can be configured to provide a characteristic impedance, such that the carrier and peaking amplifiers are presented with an impedance that is approximately the same as the characteristic impedance when both of the carrier and peaking amplifiers are turned on, and the carrier amplifier is presented with an impedance that is approximately twice the characteristic impedance when the carrier amplifier is turned on and the peaking amplifier is turned off.