Switched Power Amplifier Biasing for Low- and High-Power Efficiency
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Solution Overview
Problem
Conventional power amplifiers face inefficiencies at low output power due to high power consumption and size requirements, especially in wireless communication systems, where maintaining linearity and reducing power-added-efficiency is challenging, and existing miniaturization techniques increase the number of parts and costs.
Innovation Solution
A small size power amplifier configuration with a first and second amplifier path, where the preamplifier and peak amplifier are biased based on output power using a voltage control circuit, eliminating the need for external switches and optimizing load impedance for efficient operation at both low and high output powers without using λ/4 lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a single amplifier is used from low output power to high output power, then the saturation output power is designed to be compatible with high output power, but operation with low power-added-efficiency is unavoidable at low output power
Solution Approach 1:
The power amplifier is divided into two separate amplifiers: a first amplifier optimized for low output power operation and a second amplifier optimized for high output power operation. Each amplifier has its own load impedance matching network designed for its specific power range, allowing both to operate at high efficiency in their respective ranges without compromise.
Solution Approach 2:
An output switching circuit dynamically switches between the first and second amplifiers based on the desired output power level. The switching is controlled by a control circuit that monitors the output power requirement and selects the appropriate amplifier to maintain optimal power-added-efficiency across the full power range.
2Adaptability or versatility
If external switches are used to switch between amplifiers, then output power switching function is achieved, but mount area increases
Solution Approach 1:
The output switching circuit combines the switching function with the existing amplifier output structures, integrating the switching capability into the amplifier assembly rather than using separate external switches. This integration eliminates the need for additional mounting space while maintaining the output power switching function.
Solution Approach 2:
The first and second amplifiers are designed with universal output interfaces that can accommodate both amplifiers' connections to the common load and switching circuitry. This multi-functional design allows the same structural elements to serve multiple purposes: amplification, impedance matching, and switching, thereby reducing overall mount area.
3Power
If amplifier size is enlarged for high output power, then high output power capability is achieved, but bias current increases and power-added-efficiency decreases at low output power
Solution Approach 1:
Instead of using one large amplifier for all power levels, the system segments the amplification function into two smaller amplifiers of different sizes. The first amplifier is sized appropriately for low power operation with lower bias current, while the second amplifier is sized for high power operation. This eliminates the need to operate an oversized amplifier at low power where efficiency would be poor.
Solution Approach 2:
Each amplifier is designed with local optimization for its specific operating range: the first amplifier has load impedance matching and biasing optimized for low power operation, while the second amplifier has corresponding optimizations for high power operation. This local quality approach ensures each amplifier operates at peak efficiency in its designated power range.
Data Source
AI summary
A small size power amplifier includes a first amplifier provided for a first signal path; a second amplifier provided for said first signal path; and a third amplifier provided for a second signal path parallel to said first signal path. A voltage control circuit configured to bias one of a first set of said first amplifier and said second amplifier, and a second set of said third amplifier, based on an output power.