Outphasing Amplifier Branch Filtering for Saturated RF Efficiency

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Solution Overview

Problem

Conventional amplifiers face inefficiency and signal distortion when amplifying RF signals with high input peak to average power ratio, as they must operate in the linear region to avoid saturation, leading to bandwidth expansion and increased power requirements.

Innovation Solution

An outphasing amplifier with two phase-modulated branch signals of constant amplitude, where circuitry reduces energy in sidebands away from the central frequency while retaining phase information, and a reconstructor reasserts phase information, allowing for efficient amplification and reduced bandwidth requirements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional amplifiers operate in the linear region to avoid saturation, then signal distortion is reduced, but amplification efficiency becomes much lower

Engineering Contradiction:

Improvesignal qualityVSAvoidamplification efficiency

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The amplifier is divided into two separate amplification branches, each handling a phase-modulated signal with constant amplitude envelope. This segmentation allows each branch to operate independently at saturation without causing distortion in the combined output, resolving the contradiction between operating at saturation for efficiency and avoiding saturation for signal quality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the signal parameters by converting the amplitude-modulated input signal into two phase-modulated signals with constant amplitude envelopes. This parameter transformation enables the amplifiers to operate at saturation while maintaining signal fidelity, as the constant amplitude nature of the branch signals prevents the distortion issues that would normally arise from saturation operation.

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If outphasing amplifiers operate branch amplifiers at saturation for maximum efficiency, then amplification efficiency increases, but bandwidth expansion occurs

Engineering Contradiction:

Improveamplification efficiencyVSAvoidsignal bandwidth

Core Design Contradiction:

Use of energy by moving objectVSArea of stationary object

Solution Approach 1:

The invention extracts and removes the amplitude information from the input signal, converting it into phase-modulated signals with constant amplitude envelopes. By taking out the amplitude variations that cause bandwidth expansion and representing them through phase relationships instead, the system achieves saturation operation for efficiency while minimizing bandwidth expansion.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of directly amplifying the amplitude-modulated signal which causes bandwidth expansion, the invention inverts the approach by converting the signal into phase-modulated form with constant amplitude. This inversion allows the use of saturation-mode amplifiers while controlling bandwidth, as the phase relationships rather than amplitude variations carry the information.

Inventive Principle:

Principle #13The other way round (Inversion)

3Use of energy by moving object

If high input power is used to achieve high efficiency in conventional amplifiers, then amplification efficiency increases, but the amplifier is driven into saturation causing signal distortion

Engineering Contradiction:

Improveamplification efficiencyVSAvoidsignal fidelity

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention converts the potentially harmful effect of saturation operation into a benefit. By using phase-modulated signals with constant amplitude envelopes, the saturation non-linearity of the amplifiers actually helps to maintain constant amplitude while the phase information is preserved and combined to reconstruct the original amplitude-modulated signal without distortion.

Inventive Principle:

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

Data Source

PatentUS10116383B2Outphasing amplifier

Publication Date: 2018.10.30 NXP BV

AI summary

An outphasing amplifier having: a first branch arranged to receive and process a first branch signal, the first branch signal being phase modulated, with constant amplitude envelope; and a second branch arranged to receive and process a second branch signal, the second branch signal being phase modulated, with constant amplitude envelope, and at least a portion of the second branch signal anti-phase from the first branch signal, wherein each branch includes: circuitry arranged to process the signal to reduce the energy in sidebands of the signal away from the central frequency, while retaining the phase information in the signal; and an amplifier arranged to amplify the filtered and re-asserted branch signal.