Load-Modulated Doherty Power Amplifier for Wide Dynamic Range
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Solution Overview
Problem
Doherty power amplifiers face inefficiencies at lower power levels and are susceptible to linearity degradation due to load variations, especially in high peak-to-average ratio waveforms and when output power is not centered at the peak of the amplifier's efficiency profile, which affects their performance in advanced modulation schemes like 5G communication.
Innovation Solution
A load modulated Doherty power amplifier system that includes a combiner, a carrier amplifier, a peaking amplifier, and a load modulating amplifier, where the peaking amplifier activates at a first power threshold and the load modulating amplifier activates at a second threshold greater than the first, modulating down the load of both amplifiers to improve efficiency and linearity across a wide dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a Doherty power amplifier operates at lower power levels, then power consumption is reduced, but power added efficiency deteriorates
Solution Approach 1:
The power amplifier is segmented into three distinct amplifier stages (first amplifier, second amplifier, and third amplifier) that operate at different power thresholds. This segmentation allows each amplifier to be optimized for specific power ranges, with the first amplifier handling lower power levels and the second and third amplifiers activating at higher thresholds to maintain efficiency during power back-off conditions.
Solution Approach 2:
The system dynamically adjusts which amplifier stage is active based on the input signal power level. The saturation detector continuously monitors the first amplifier's saturation state and dynamically controls the activation of the second and third amplifiers through bias circuits, enabling the system to adapt its efficiency profile across varying power levels.
2Loss of information
If a Doherty power amplifier handles high peak-to-average ratio waveforms, then signal fidelity is improved, but linearity deteriorates due to load variations
Solution Approach 1:
Each amplifier stage is assigned a specific operational role with tailored biasing conditions. The first amplifier operates in a linear region for lower power levels, while the second amplifier (class C biased) and third amplifier (class C biased) are optimized for peak power handling. This local optimization of quality characteristics for different power ranges maintains linearity during power back-off while handling high peak-to-average ratio waveforms.
Solution Approach 2:
A saturation detector provides feedback by monitoring the saturation state of the first amplifier and dynamically controlling the bias conditions of the second and third amplifiers. This feedback mechanism ensures that the auxiliary amplifiers activate at appropriate moments to maintain linearity and signal fidelity during high peak-to-average ratio waveform transmission.
3Use of energy by moving object
If output power is not centered at the peak of the amplifier's efficiency profile, then power consumption is reduced, but power added efficiency deteriorates
Solution Approach 1:
The system changes the operational parameters (which amplifier stage is active) based on the input power level. By having multiple amplifier stages with different efficiency profiles and activation thresholds, the system can maintain operation near the peak efficiency point across a wider dynamic range, even when output power varies and is not centered at the original efficiency peak.
4Loss of energy
If a load modulating amplifier is added to modulate down the load, then power added efficiency is improved, but device complexity increases
Solution Approach 1:
The load modulation function is merged with the power amplification function by using the third amplifier to simultaneously provide power amplification and load modulation. The third amplifier's output is combined with the first and second amplifiers through a combiner, allowing it to modulate the load seen by the other amplifiers while also contributing to the overall power output, thus reducing the need for separate dedicated load modulation circuitry.
Data Source
AI summary
Load modulated Doherty power amplifiers are provided herein. In certain embodiments, a load modulated Doherty power amplifier includes a combiner, a carrier amplifier having an output coupled to a first terminal of the combiner, a peaking amplifier having an output coupled to a second terminal of the combiner, a load modulating amplifier having an output coupled to a third terminal of the combiner, and a radio frequency (RF) output port that is coupled to a fourth terminal of the combiner and provides an RF output signal. The peaking amplifier is operable to activate at a first power threshold, while the load modulating amplifier is operable to activate at a second power threshold to modulate down a load of the carrier amplifier and of the peaking amplifier.