Linear Microwave Power Amplifier Biasing for IM3 and Efficiency
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Solution Overview
Problem
Microwave power amplifiers face challenges in simultaneously achieving high efficiency and low third-order intermodulation (IM3) distortion, as existing technologies often compromise between efficiency and linearity, and conventional cascading arrangements can promote intermodulation harmonics and distortion.
Innovation Solution
A two-stage amplifier configuration is employed, where a low distortion first stage is coupled with a high efficiency second stage, using dynamic biasing to modulate DC bias voltages based on input and output power levels, and incorporating a directional coupler and processor for feedback correction to minimize nonlinearity, with a post-distortion approach that reverses the conventional biasing order from class B to class C for improved efficiency and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional cascading arrangements are used to achieve high efficiency, then efficiency is improved, but intermodulation harmonics and distortion increase
Solution Approach 1:
The patent inverts the conventional biasing order in cascaded amplifiers. Instead of using class B or class AB biasing in the first stage followed by class C in the second stage, the patent applies class C biasing in the first stage and class B or class AB in the second stage. This inversion allows the first stage to operate at high efficiency while the second stage provides linearization, thereby reducing intermodulation distortion while maintaining overall high efficiency.
Solution Approach 2:
The patent changes the biasing parameters of the amplifier stages dynamically. By adjusting the bias point of the transistors in each stage according to the operating conditions, the patent optimizes the trade-off between efficiency and linearity. The biasing circuitry modifies the DC operating point to achieve class C operation in the first stage for maximum efficiency and class B/AB in the second stage for distortion reduction.
2Use of energy by moving object
If class B biasing is used to improve efficiency, then efficiency is improved, but linearity deteriorates
Solution Approach 1:
The patent segments the amplifier function into two distinct stages with different biasing characteristics. The first stage is biased in class C for maximum efficiency, while the second stage is biased in class B or class AB for improved linearity. This segmentation allows each stage to optimize for its specific function, with the overall system achieving both high efficiency and acceptable linearity through the combination of stages.
Solution Approach 2:
The patent employs feedback mechanisms to correct the nonlinearity introduced by class B or class AB biasing in the second stage. The feedback circuitry monitors the output signal and adjusts the biasing or input signal characteristics to compensate for distortion, thereby improving overall linearity while maintaining the efficiency benefits of class B/AB operation in the second stage.
Data Source
AI summary
A post-distortion method for cascading amplifier stages in a two-stage microwave power amplifier and a dynamic biasing method using back-end processing for correcting nonlinearity in the power amplifier output. A first or driver stage biased in a near-A region with low distortion is cascaded with a second or power stage biased in a near-C region with high efficiency. The amplitude and phase responses of the two stages compensate another to yield a more linear overall gain for the overall power amplifier. The dynamic biasing scheme modulates the source to drain voltages of the transistors used in the amplifier stages based on the harmonics in amplifier output in order to minimize the harmonics and correct non-linearity in the output.