Symmetrical Doherty Amplifier With Two-Stage Peaking Gain Control
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Solution Overview
Problem
Conventional Doherty amplifiers face inefficiencies in power back-off and gain performance, particularly in high-power regions, and existing solutions to improve these aspects often compromise bandwidth performance.
Innovation Solution
A two-stage peaking amplifier configuration is introduced, where the second peaking amplifier is designed to turn on later and have a faster rise in gain compared to conventional Doherty amplifiers, combined with an RF coupler that divides the input signal to provide higher power to the main amplifier, enhancing output power back-off efficiency and gain without significantly affecting bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional single-stage peaking amplifier is used in a Doherty amplifier, then the device complexity is lower, but the efficiency in deep-output power back-off region deteriorates
Solution Approach 1:
The peaking amplifier is divided into two cascaded stages instead of using a single stage. The first peaking amplifier stage and second peaking amplifier stage are connected in cascade, allowing each stage to contribute to different portions of the power back-off region. This segmentation enables improved efficiency in deep-output power back-off while managing device complexity through modular design.
2Loss of energy
If the peaking amplifier turns on earlier with slower gain rise, then the bandwidth performance is improved, but the efficiency in deep-output power back-off region deteriorates
Solution Approach 1:
The patent implements dynamic control of the peaking amplifier stages through separate biasing circuits. The first peaking amplifier is biased to turn on at a certain power level, while the second peaking amplifier is biased to turn on at a different power level. This dynamic, staged activation allows the system to optimize efficiency across different power back-off regions while maintaining appropriate gain rise characteristics.
3Loss of energy
If higher power is provided to the main amplifier through the RF coupler, then the output power back-off efficiency is improved, but the signal distribution balance deteriorates
Solution Approach 1:
An RF coupler is introduced as an intermediary device to distribute the input signal between the main amplifier and the peaking amplifier stages. The RF coupler provides controlled signal splitting with specific coupling values, enabling the main amplifier to receive higher power for improved back-off efficiency while maintaining proper signal distribution through its inherent coupling characteristics.
Data Source
AI summary
Apparatus and methods for an improved-efficiency Doherty amplifier are described. The Doherty amplifier may include a two-stage peaking amplifier that transitions from an “off” state to an “on” state later and more rapidly than a single-stage peaking amplifier used in a conventional Doherty amplifier. The improved Doherty amplifier may operate at higher gain values than a conventional Doherty amplifier, with no appreciable reduction in signal bandwidth.