Cascode Power Amplifier Impedance Ratio for Power-Efficiency Balance
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Solution Overview
Problem
Power amplifier circuits face a trade-off between output power and power-added efficiency, where decreasing output impedance increases output power but decreases efficiency, and increasing output impedance improves efficiency but decreases power. An optimal balance between these two is desirable.
Innovation Solution
A power amplifier circuit configuration with a cascode structure, utilizing multiple transistors and capacitors, where the collector impedance of one transistor is set to a ratio greater than or equal to 2.2 and less than or equal to 2.7 relative to another, achieving a desired trade-off between output power and power-added efficiency without increasing the power supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If output impedance is decreased, then output power is increased, but power-added efficiency is decreased
Solution Approach 1:
The power amplifier is divided into two separate amplifier stages (first power amplifier and second power amplifier) with distinct impedance characteristics. The first amplifier operates with lower output impedance to maximize output power, while the second amplifier operates with higher output impedance to maximize efficiency. This segmentation allows each stage to optimize for its specific function, resolving the contradiction between power and efficiency.
Solution Approach 2:
Different impedance characteristics are applied to different parts of the system. The first power amplifier stage is designed with specific impedance values optimized for power delivery, while the second stage is designed with different impedance values optimized for efficiency. This local differentiation of quality parameters allows simultaneous optimization of both contradictory requirements in different locations of the system.
2Loss of energy
If output impedance is increased, then power-added efficiency is increased, but output power is decreased
Solution Approach 1:
The power amplifier is divided into two separate amplifier stages (first power amplifier and second power amplifier) with distinct impedance characteristics. The first amplifier operates with lower output impedance to maximize output power, while the second amplifier operates with higher output impedance to maximize efficiency. This segmentation allows each stage to optimize for its specific function, resolving the contradiction between power and efficiency.
Solution Approach 2:
Different impedance characteristics are applied to different parts of the system. The first power amplifier stage is designed with specific impedance values optimized for power delivery, while the second stage is designed with different impedance values optimized for efficiency. This local differentiation of quality parameters allows simultaneous optimization of both contradictory requirements in different locations of the system.
3Power
If power supply voltage is increased, then output power is increased, but device complexity is increased due to booster circuit requirement
Solution Approach 1:
Instead of using a single high-voltage amplifier or a complex booster circuit, the system is segmented into two lower-voltage amplifier stages. Each amplifier operates at a manageable voltage level, eliminating the need for complex voltage boosting mechanisms while achieving the required total output power through the cascaded configuration.
Data Source
AI summary
A power amplifier circuit includes a first transistor, a capacitor, and a second transistor. The first transistor has an emitter electrically connected to a reference potential, a base, and a collector electrically connected to a first power supply potential. A first end of the capacitor is electrically connected to the collector of the first transistor. The second transistor has an emitter electrically connected to a second end of the capacitor and electrically connected to the reference potential, a base, and a collector electrically connected to the first power supply potential. An RF output signal obtained by amplifying the RF input signal is output from the collector of the second transistor. A second bias circuit includes a third transistor having a collector electrically connected to a second power supply potential, a base, and an emitter from which the second bias current or voltage is output.