Asymmetric Multilevel Outphasing RF Amplifiers for Wideband Efficiency

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Solution Overview

Problem

Conventional RF transmitter architectures face challenges in achieving high efficiency and linearity, particularly for high data-rate communication standards like WiMAX, due to inefficiencies in power amplifiers and combiners, leading to wasted energy and signal distortion.

Innovation Solution

The asymmetric multilevel outphasing (AMO) transmitter architecture and outphasing energy recovery amplifier (OPERA) design, which utilize a switch network to supply discrete voltages to power amplifiers and incorporate a resistance compression network to reduce impedance variation, thereby enhancing efficiency and linearity across a wide power range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If conventional polar architecture is used to improve power amplifier efficiency, then efficiency is improved, but bandwidth is limited due to converter bandwidth expansion

Engineering Contradiction:

Improvepower amplifier efficiencyVSAvoidbandwidth

Core Design Contradiction:

Use of energy by moving objectVSSpeed

Solution Approach 1:

The invention segments the amplitude modulation function from the power converter by using multiple power amplifiers with constant-envelope signals instead of a single amplifier with variable envelope. This eliminates the need for wide-bandwidth power supply modulation, resolving the bandwidth limitation while maintaining efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of modulating the power supply amplitude to achieve variable envelope (conventional polar approach), the invention inverts the approach by using constant-envelope signals and achieving amplitude variation through coherent combination of multiple amplifiers. This reverses the modulation strategy to avoid bandwidth expansion.

Inventive Principle:

Principle #13The other way round (Inversion)

2Use of energy by moving object

If conventional LINC architecture with isolating combiner is used to enable efficient switching mode power amplifiers, then amplifier efficiency is improved, but power is wasted as heat in the isolation resistor

Engineering Contradiction:

Improvepower amplifier efficiencyVSAvoidpower wasted in isolation resistor

Core Design Contradiction:

Use of energy by moving objectVSLoss of energy

Solution Approach 1:

The invention converts the previously harmful isolation resistor into a beneficial impedance-matching element. By using a resistive combiner with proper impedance transformation, the isolation resistance becomes part of the efficient power combining process, eliminating power waste while maintaining amplifier isolation and efficiency.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Manufacturing precision

If conventional LINC architecture is used to achieve high data-rate communication, then linearity is improved, but overall efficiency deteriorates due to high PAPR

Engineering Contradiction:

Improvesignal linearityVSAvoidoverall system efficiency

Core Design Contradiction:

Manufacturing precisionVSUse of energy by moving object

Solution Approach 1:

The invention merges the previously separate and lossy isolation function with the power combining function into a single efficient resistive combiner structure. This integration eliminates the dual penalty of isolation losses and combining losses, achieving both high linearity for high data-rate communication and high overall efficiency even with high PAPR signals.

Inventive Principle:

Principle #5Merging (Combining)

4Use of energy by moving object

If asymmetric multilevel outphasing architecture is used to minimize amplifier outphasing angles, then efficiency is improved, but device complexity increases due to switch network and multiple voltage levels

Engineering Contradiction:

Improvetransmitter efficiencyVSAvoidswitch network complexity

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The invention segments the voltage control into discrete levels using switch networks, allowing efficient operation at multiple power levels. This segmentation enables the system to minimize outphasing angles and maximize efficiency at each operating point while managing complexity through structured voltage level management.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention dynamically adjusts the operating voltage levels and amplifier configurations based on signal conditions to maintain optimal efficiency. The switch network enables dynamic selection of voltage levels, allowing the system to adapt to varying power requirements while minimizing outphasing angles and maximizing overall efficiency.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS8659353B2Asymmetric multilevel outphasing architecture for RF amplifiers

Publication Date: 2014.02.25 MASSACHUSETTS INST OF TECH

AI summary

A radio frequency (RF) circuit includes a power supply configured to generate a plurality of voltages, a plurality of power amplifiers, each having an RF output port and a power supply input port, a switch network having a plurality of input ports coupled to the power supply and a plurality of switch network output ports coupled to the power supply input ports of the plurality of power amplifiers, wherein the switch network is configured to output selected ones of the plurality of voltages from the plurality of switch network output ports, at least two of the switch network output port voltages capable of being different ones of the plurality of voltages, and an RF power combiner circuit having a plurality of input ports coupled to RF output ports of the plurality of power amplifiers and an output port at which is provided an output signal of the RF circuit.