Multi-Stage Power Amplifier Gain Matching Near Saturation
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Solution Overview
Problem
Conventional power amplifiers face challenges in maintaining linearity near the saturation point, especially in high output power conditions, where distortion and power efficiency are reciprocal, leading to suboptimal performance.
Innovation Solution
A power amplifier design with multiple stages, each stage comprising amplification elements and distortion compensation circuits, where the gain characteristics of adjacent stages are adjusted to be concave and convex respectively, allowing their combination to achieve a flat and linear gain characteristic across the entire output range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If output electric power is increased to approach saturation, then power efficiency is improved, but distortion increases and linearity deteriorates
Solution Approach 1:
The power amplifier is divided into multiple amplification stages (first amplification stage with first and second amplification elements, second amplification stage with third amplification element). Each stage has its own distortion compensation circuit, allowing independent optimization of linearity and power efficiency at different operating points. This segmentation enables the system to achieve both high power efficiency and low distortion by combining the outputs of multiple stages with complementary characteristics.
Solution Approach 2:
Different amplification elements are biased at different operating points (Class A, Class AB, or Class B) depending on their specific function within the multi-stage architecture. The first amplification element may operate at Class A for high linearity, while the second and third elements operate at Class AB or Class B for higher power efficiency. This local optimization of bias conditions allows each element to contribute its strengths to the overall performance.
2Manufacturing precision
If distortion compensation is applied to all amplification elements, then linearity is improved, but device complexity increases
Solution Approach 1:
Distortion compensation circuits are selectively applied to specific amplification elements based on their operating conditions and contribution to overall distortion. The patent shows that not all amplification elements require identical distortion compensation, allowing the system to achieve adequate linearity with reduced circuit complexity compared to compensating every element equally.
Solution Approach 2:
The multiple amplification stages act as intermediaries that process the signal in sequence, with each stage contributing to the final output. By strategically placing distortion compensation circuits at specific stages rather than at every element, the system achieves effective distortion management while minimizing the total number of compensation circuits required.
Data Source
AI summary
A power amplifier includes a front-stage amplifier including first and second transistors connected in parallel, and a rear-stage amplifier including a third transistor. The first transistor is biased into near-Class A without a distortion compensation circuit. The second and third transistors are biased into near-Class B with a distortion compensation circuit. The gain characteristics of the first to third transistors are adjusted so that the concave portion of the gain characteristics of the front-stage amplifier and the convex portion of the gain characteristics of the rear-stage amplifier match each other, to thereby flatten the gain characteristic of the entire power amplifier.