Class-E Outphasing Amplifier Combiner for Back-Off Efficiency
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Solution Overview
Problem
Class-E outphasing power amplifiers face inefficiencies at low power levels and high peak-to-average power ratios, leading to reduced battery life in handheld devices and increased heat sinking costs in base stations, with existing techniques failing to effectively increase power efficiency and peak output power without violating transistor reliability limits.
Innovation Solution
The implementation of a differential class-E outphasing power amplifier with efficiency and power enhancement circuits, including reactive elements and harmonic signal addition, to improve power efficiency and peak output power across a range of power back-off conditions without exceeding transistor voltage specifications, using alternative combiner circuit configurations that do not rely on quarter-wavelength transmission lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional class-E outphasing power amplifiers are used, then the amplifier can operate at high peak power levels, but power efficiency deteriorates at low power levels (power back-off conditions)
Solution Approach 1:
The power amplifier is divided into two separate class-E power amplifiers operating in parallel, each handling a portion of the total power. This segmentation allows independent optimization of each amplifier's operation, enabling one amplifier to maintain high efficiency while the other handles peak power demands, thus resolving the contradiction between peak power capability and back-off efficiency.
Solution Approach 2:
The system dynamically adjusts the operating state of the two power amplifiers based on the instantaneous power demand. During peak power conditions, both amplifiers operate actively; during back-off conditions, one amplifier can be turned off or operated at reduced power, dynamically adapting to maintain optimal efficiency across varying power levels.
2Power
If power supply voltage is increased to boost peak output power, then peak output power improves, but transistor reliability is compromised due to exceeding voltage specifications
Solution Approach 1:
The total voltage stress is segmented and distributed across two separate power amplifier circuits. Each amplifier operates at a reduced voltage level compared to a single amplifier design, allowing the system to achieve higher peak output power through combined operation while keeping individual transistor voltage stresses within safe reliability limits.
Solution Approach 2:
Two power amplifiers are merged in parallel configuration to achieve combined peak output power that exceeds what a single amplifier could deliver. The merging allows the system to attain high power levels without requiring any single transistor to withstand excessive voltage, thus maintaining reliability while boosting peak power capability.
3Ease of operation
If quarter-wavelength transmission lines are used in the combiner circuit, then the combiner can achieve proper signal combining, but device complexity increases
Solution Approach 1:
The complex quarter-wavelength transmission line elements are extracted and replaced with simpler lumped reactive elements (inductors and capacitors). This extraction maintains the essential signal combining function while eliminating the need for precise transmission line implementations, thereby reducing device complexity and improving ease of manufacturing and tuning.
Solution Approach 2:
The distributed transmission line structure is replaced with lumped electrical elements (inductors and capacitors). This substitution transforms a mechanically complex transmission line-based combiner into a simpler circuit implementation using discrete reactive components, reducing device complexity while preserving the signal combining functionality.
Data Source
AI summary
An outphasing amplifier includes a first class-E power amplifier having an output coupled to a first conductor and an input receiving a first RF drive signal. A first reactive element is coupled between the first conductor and a second conductor. A second reactive element is coupled between the second conductor and a third conductor. A second class-E power amplifier includes an output coupled to a fourth conductor and an input coupled to a second RF drive signal, a third reactive element coupled between the second and fourth conductors. Outputs of the first and second power amplifiers are combined by the first, second and third reactive elements to produce an output current in a load. An efficiency enhancement circuit is coupled between the first and fourth conductors to improve power efficiency at back-off power levels. Power enhancement circuits are coupled to the first and fourth conductors, respectively.