Symmetric Doherty Amplifier Phase-Shifted Load Modulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Doherty amplifiers face limitations in achieving high efficiency at high output back-off (OBO) due to the requirement for asymmetric amplifier sizes, which restricts maximum RF output power and complicates design, especially for three-way Doherty amplifiers, and existing solutions like envelope tracking add complexity.
Innovation Solution
A symmetric Doherty amplifier circuit with equally sized main and peaking amplifiers dynamically controls the VSWR by shifting the phase at the peaking amplifier's output, allowing efficient operation across a wide OBO range by adjusting the load impedance seen by the main amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If asymmetric amplifier sizes are used to achieve high efficiency at high OBO, then efficiency at high output back-off is improved, but maximum RF output power is limited and device complexity increases
Solution Approach 1:
The patent applies dynamics by making the load impedance seen by the main amplifier dynamically adjustable through phase shift circuitry. The phase of the signal from the peaking amplifier is shifted to control the VSWR, which in turn dynamically adjusts the load impedance on the main amplifier to optimize efficiency at different OBO levels while maintaining high power capability
Solution Approach 2:
The patent changes the electrical parameter of phase angle in the peaking amplifier output to control the VSWR and subsequently the load impedance on the main amplifier. By adjusting this phase parameter, the system achieves high efficiency at high OBO without requiring asymmetric amplifier sizing
2Loss of energy
If asymmetric amplifier sizes are used to achieve high efficiency at high OBO, then efficiency at high output back-off is improved, but device complexity and design difficulty increase
Solution Approach 1:
The patent uses controlled asymmetry in the sense that while amplifier sizes are symmetric, the phase shift introduced by the peaking amplifier creates an asymmetric load modulation effect on the main amplifier. This resolves the contradiction by achieving the benefits of asymmetric design without the physical asymmetry
Solution Approach 2:
The phase shift circuitry acts as an intermediary between the peaking amplifier and the main amplifier, controlling the VSWR and load impedance without requiring direct asymmetric amplifier sizing. This intermediary mechanism simplifies the overall design while achieving high efficiency at high OBO
3Loss of energy
If three-way Doherty amplifiers are used to operate at more than 6 dB OBO, then efficiency at high OBO is improved, but device complexity and physical layout size increase
Solution Approach 1:
The phase shift circuitry in the two-way Doherty amplifier performs multiple functions: it controls VSWR, adjusts load impedance, and enables operation at various OBO levels (6 dB to 12 dB or more). This multi-functionality replaces the need for additional amplifier stages while achieving the same high OBO performance
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
Enables high efficiency operation from 6 dB to 12 dB OBO or more by dynamically shifting the phase, increasing load impedance and efficiency, without the need for asymmetric amplifier sizes or complex system redesigns.
Implementation Method 1
phase shift circuitry configured to shift the phase at the output of the peaking amplifier at OBO so that a load impedance seen by the main amplifier and efficiency of the symmetric Doherty amplifier both increase at OBO as a function of the phase shift at the peaking amplifier output
Data Source
AI summary
A symmetric Doherty amplifier includes a main amplifier and a peaking amplifier of the same size as the main amplifier. The symmetric Doherty amplifier is configured to operate at peak output power when the main amplifier and the peaking amplifier are each in saturation, and at output-back-off (OBO) when the main amplifier is in saturation and the peaking amplifier is not in saturation. Phase shift circuitry is configured to shift the phase at an output of the peaking amplifier at OBO so that a load impedance seen by the main amplifier and efficiency of the symmetric Doherty amplifier both increase at OBO as a function of the phase shift at the peaking amplifier output.