Symmetrical Doherty Amplifier With Two-Stage Peaking Back-Off Efficiency
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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 and second peaking amplifier are connected in cascade, with each stage contributing to different portions of the power back-off region. This segmentation allows the amplifiers to operate more efficiently across a wider range of output power levels, particularly improving efficiency in the deep-back-off region where a single stage would be inefficient.
2Loss of energy
If the peaking amplifier turns on early with slow gain rise, then the bandwidth performance is maintained, but the efficiency in high-power regions deteriorates
Solution Approach 1:
The patent implements dynamic control of the peaking amplifier stages through biasing circuits that adjust the turn-on timing and gain characteristics. The first peaking amplifier is biased to turn on at a certain power level, while the second peaking amplifier is biased to turn on later with a faster gain rise. This dynamic configuration allows optimization of efficiency at different power levels without compromising bandwidth, as the system adapts its characteristics based on the operating conditions.
3Loss of energy
If an RF coupler is used to divide input signal with higher power to main amplifier, then the output power back-off efficiency is improved, but the device complexity increases
Solution Approach 1:
An RF coupler is introduced as an intermediary device to divide the input signal between the main amplifier and the first peaking amplifier. The coupler provides a controlled power split, directing a larger portion of the input power to the main amplifier and a smaller portion to the peaking amplifier stage. This intermediary component enables optimized power distribution that improves overall efficiency, particularly in the deep-back-off region, while the coupler's design minimizes the increase in device complexity.
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.