Multiclass Power Amplifier Architecture Without Load Modulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional Doherty amplifiers experience load modulation issues due to impedance changes with peaking amplifiers transitioning between idle and active states, leading to reduced efficiency and bandwidth limitations, especially with increasing peak-to-average power ratios in communication signals.
Innovation Solution
A multiclass power amplifier architecture with parallel circuit branches, where main and peaking amplifiers operate in different classes, and impedance inverters maintain consistent load impedance for the main amplifier, eliminating load modulation and enhancing efficiency and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional Doherty amplifiers use peaking amplifiers transitioning between idle and active states, then power efficiency is improved at high signal levels, but load modulation occurs causing bandwidth limitations and reduced efficiency
Solution Approach 1:
An impedance inverter is introduced as an intermediary component between the peaking amplifier and the combining node. This impedance inverter maintains a consistent impedance transformation ratio regardless of the peaking amplifier's state (idle or active), thereby preventing load modulation on the main amplifier and ensuring stable bandwidth performance while preserving the power efficiency benefits of the Doherty architecture.
2Power
If peaking amplifiers are activated at high signal levels, then output power capability is improved, but impedance changes cause load modulation of the main amplifier
Solution Approach 1:
The impedance inverter serves as a mediator that decouples the impedance changes of the peaking amplifier from the main amplifier. By placing the impedance inverter in series with the peaking amplifier output, the system achieves high output power capability through peaking amplifier activation while the impedance inverter maintains stable impedance conditions for the main amplifier, eliminating load modulation effects.
3Loss of energy
If multiple amplifiers operate in parallel in different classes, then amplification efficiency is improved, but maintaining consistent load impedance becomes more complex
Solution Approach 1:
The impedance inverter's transformation ratio is specifically designed and tuned to compensate for the impedance changes that occur when peaking amplifiers transition between idle and active states. By adjusting the impedance inverter's electrical length and characteristic impedance, the system maintains consistent load impedance on the main amplifier while allowing multiple amplifiers to operate in parallel in different classes for improved efficiency.
Data Source
AI summary
Apparatus and methods for a no-load-modulation power amplifier are described. No-load-modulation power amplifiers can comprise multiple amplifiers connected in parallel to amplify a signal that has been divided into parallel circuit branches. One of the amplifiers can operate as a main amplifier in a first amplification class and the remaining amplifiers can operate as peaking amplifiers in a second amplification class. The main amplifier can see essentially no modulation of its load between the power amplifier's fully-on and fully backed-off states. The power amplifiers can operate in symmetric and asymmetric modes. Improvements in bandwidth and drain efficiency over conventional Doherty amplifiers are obtained. Further improvements can be obtained by combining signals from the amplifiers with hybrid couplers.