Doherty Power Amplifier Delay Compensation for Back-Off Efficiency
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Solution Overview
Problem
Conventional Doherty power amplifiers face inefficiencies due to premature active-load pulling by auxiliary power amplifiers before the main power amplifier reaches saturation, affecting overall efficiency, especially for non-constant envelope signals with high peak-to-average ratios.
Innovation Solution
The implementation of a Doherty power amplifier with multiple levels of auxiliary power amplifiers and a delay device to compensate for group delay differences between the main and auxiliary power amplification branches, ensuring the main power amplifier remains closer to saturation and improving efficiency by preventing premature active-load pulling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional Doherty power amplifier uses an auxiliary power amplifier biased to class C working state, then the auxiliary power amplifier can provide gain amplification, but the auxiliary power amplifier starts to perform active-load pulling before the main power amplifier reaches saturation, causing the main power amplifier to not reach saturated state and reducing efficiency
Solution Approach 1:
The patent applies preliminary action by introducing a delay device in the main power amplification branch that compensates for the group delay difference between the main and auxiliary power amplification branches. This ensures that the auxiliary power amplifier's active-load pulling effect occurs at the correct timing when the main power amplifier has reached saturation, rather than prematurely. The delay device pre-adjusts the signal timing to synchronize the operation of both amplifiers, resolving the efficiency problem caused by premature active-load pulling.
2Productivity
If the auxiliary power amplifier is turned on early to provide amplification, then the amplification capability is improved, but the main power amplifier cannot maintain saturated state, affecting overall efficiency during power back-off
Solution Approach 1:
The delay device performs preliminary timing adjustment on the main power amplification branch signal to compensate for the faster response of the auxiliary power amplifier. This ensures that when the auxiliary power amplifier starts amplifying, the main power amplifier has already reached saturation, maintaining the correct operational sequence and efficiency characteristics during power back-off conditions.
3Loss of energy
If multiple levels of auxiliary power amplifiers are used, then the efficiency during power back-off is improved, but the group delay difference between branches causes premature active-load pulling
Solution Approach 1:
The delay device compensates for the cumulative group delay difference introduced by multiple levels of auxiliary power amplifiers. By pre-adjusting the timing in the main power amplification branch, the system maintains synchronized operation despite the additional delay stages, ensuring that active-load pulling occurs at the correct moment and efficiency is optimized.
Solution Approach 2:
The patent changes the timing parameter of the main power amplification branch by introducing a delay equal to the group delay difference. This parameter adjustment synchronizes the operational characteristics of the main and auxiliary branches, resolving the timing mismatch caused by multiple auxiliary amplifier levels while maintaining improved efficiency during power back-off.
Data Source
AI summary
A Doherty power amplifier (100) includes: a first amplification circuit (110), including a main power amplification branch and at least one auxiliary power amplification branch; a delay device (383), connected in the main power amplification branch; a combiner network (140), configured to: perform impedance inversion on the first amplification circuit (110), and couple an output end of the main power amplification branch and an output end of the at least one auxiliary power amplification branch to a load (160); and a first power divider (130), connected to an input end of the main power amplification branch and an input end of the at least one auxiliary power amplification branch, and configured to allocate an input signal of the first power divider (130) to the main power amplification branch and the at least one auxiliary power amplification branch.