Doherty Power Amplifier Impedance Transformation for High-PAPR Efficiency
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Solution Overview
Problem
Traditional Doherty power amplifiers face challenges in maintaining high efficiency with peak to average power ratios (PAPR) greater than 6 dB due to limited peaking amplifier off-state impedance, leading to compromised carrier/main amplifier back-off efficiency.
Innovation Solution
The proposed power amplifier design includes a splitter network, carrier amplifier path, and peaking amplifier path with impedance transformers to enhance peaking amplifier off-state impedance, allowing for higher impedance transformation ratios and improved power matching, reducing power leakage and enhancing carrier amplifier efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional Doherty architecture is used, then efficiency is improved for moderate PAPR signals, but efficiency deteriorates for PAPR greater than 6 dB due to limited peaking amplifier off-state impedance
Solution Approach 1:
The patent transforms the peaking amplifier off-state impedance from a fixed low value to a dynamically enhanced high value using impedance transformation networks. This parameter change allows the peaking amplifier to present high impedance during off-state (improving efficiency) while maintaining proper loading during on-state (enabling high PAPR operation).
Solution Approach 2:
The patent introduces impedance transformation networks as intermediary elements between the peaking amplifier and the junction node. These networks mediate the impedance mismatch, transforming the peaking amplifier's natural low off-state impedance into an enhanced high impedance value, thereby resolving the contradiction between efficiency and PAPR handling.
2Ease of manufacture
If peaking amplifier off-state impedance is low, then power matching is simplified, but power leakage increases and carrier amplifier efficiency decreases
Solution Approach 1:
The patent changes the impedance parameter of the peaking amplifier from low to high during off-state using transformation networks. This parameter change reduces power leakage by preventing carrier amplifier signal from leaking into the peaking amplifier path, while the networks are designed to maintain proper power matching during on-state operation.
3Loss of energy
If impedance transformation ratio is increased to enhance peaking off-state impedance, then carrier amplifier efficiency is improved, but device complexity increases
Solution Approach 1:
The patent segments the impedance transformation function into separate networks for the peaking amplifier path and carrier amplifier path. This segmentation allows each network to be optimized independently, achieving the required impedance transformation ratios while managing overall device complexity through modular design.
Solution Approach 2:
The patent employs asymmetric impedance transformation where the peaking amplifier path and carrier amplifier path have different transformation ratios tailored to their specific requirements. The peaking path uses a higher transformation ratio to achieve enhanced off-state impedance, while the carrier path uses a lower ratio to maintain proper loading, optimizing efficiency without uniform complexity.
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 enhanced peaking off-state impedance improves the power added efficiency and reduces power leakage, resulting in increased carrier amplifier efficiency and broader bandwidth performance.
Implementation Method 1
The peaking amplifier path further comprises a first impedance transformer coupled between an output of the peaking output matching network and the junction node to enhance the off-state impedance of the peaking amplifier
Implementation Method 2
The carrier amplifier path further comprises a second impedance transformer coupled between an output of the carrier output matching network and the junction node
Data Source
AI summary
A power amplifier is disclosed for amplifying an input signal and providing an amplified signal to a load at a junction node. The power amplifier comprises a splitter network, a carrier amplifier path and a peaking amplifier path. The peaking amplifier path comprises a first impedance transformer coupled between a peaking output matching network and the junction node to enhance the off-state impedance of the peaking amplifier. The carrier amplifier path comprises a second impedance transformer coupled between a carrier output matching network and the junction node.