Class-F Power Amplifier Harmonic Termination for Higher PAE
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Solution Overview
Problem
There is a need for improved radio frequency (RF) power amplifiers with increased power added efficiency (PAE) to extend battery life in smartphones, particularly for high peak-to-average-power ratio signals like LTE, while maintaining high efficiency and meeting gain and output power specifications, which is challenging due to limitations in miniature component integration and harmonic management.
Innovation Solution
A Class-F RF power amplifier design using a hybrid output network with discrete SMT components, wirebonds, and on-die chip capacitors, featuring termination circuits that provide short circuits at even harmonics and open circuits at odd harmonics, and a resonant circuit that blocks odd harmonics, along with an envelope tracking modulator to optimize collector voltage and current waveforms for high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional power amplifier designs are used, then device simplicity is maintained, but power added efficiency is insufficient for high peak-to-average-power ratio signals
Solution Approach 1:
The output network is segmented into multiple discrete components including series LC circuits for even harmonic termination and parallel LC circuits for odd harmonic blocking. This segmentation allows independent optimization of each harmonic termination, achieving ultra-high efficiency by precisely controlling voltage and current waveforms at specific harmonics without requiring a completely redesigned complex system
Solution Approach 2:
The termination circuits serve multiple functions simultaneously: they terminate even harmonics through short circuits, block odd harmonics through open circuits, and shape the overall voltage and current waveforms to achieve Class-F operation. This multi-functionality allows a single termination network to accomplish what would otherwise require multiple separate circuits, improving efficiency without proportionally increasing complexity
2Use of energy by moving object
If harmonic termination circuits are added to improve efficiency, then power added efficiency increases, but component count and area increase
Solution Approach 1:
The series LC circuits for even harmonic termination and parallel LC circuits for odd harmonic blocking are merged into a single integrated output network. This combined approach allows simultaneous harmonic termination and waveform shaping using one cohesive circuit structure rather than separate independent circuits, achieving high efficiency while minimizing the total component count and footprint
Solution Approach 2:
The termination circuits are designed to dynamically affect multiple harmonics simultaneously through their resonant properties. The series LC circuits provide dynamic short circuits at even harmonics while the parallel LC circuits provide dynamic open circuits at odd harmonics, allowing a single static circuit configuration to achieve dynamic harmonic control without requiring active components or multiple switches
3Use of energy by moving object
If Class-F operation with harmonic control is implemented, then efficiency reaches ultra-high levels, but manufacturing precision requirements increase
Solution Approach 1:
The design utilizes parameter changes in the LC circuit components to achieve the desired harmonic termination characteristics. By carefully selecting the inductance and capacitance values for each LC circuit, the resonant frequencies are tuned to specific harmonic frequencies, allowing precise control over voltage and current waveforms. This parameter-based approach enables manufacturing tolerance compensation through design optimization rather than requiring extremely tight component tolerances
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves ultra-high efficiency of about 80% for low-band and 75% for ultra-high-band frequencies, outperforming existing designs without increasing component count or area, and provides linear power with reduced noise and stability concerns.
Implementation Method 1
The series LC circuit is configured to provide a short circuit at a second harmonic of the RF signal
Implementation Method 2
The parallel LC circuit can block a fundamental frequency of the amplified RF signal
Data Source
AI summary
Aspects of this disclosure relate to efficient power amplifiers, such as class-F power amplifiers. A power amplifier transistor can provide an amplified RF signal. A termination can be coupled to an output of the power amplifier transistor and configured to provide a short circuit at a second harmonic. In some instances, the termination circuit can provide an open circuit at a third harmonic. A resonant circuit can be coupled to the output terminal of the power amplifier transistor and configured to provide an open circuit at the third harmonic. In certain embodiments, an input termination circuit coupled to an input terminal of the power amplifier transistor can provide a short circuit at the second harmonic. The power amplifiers of this disclosure can be implemented, for example, in envelope tracking applications.