RF-Coupled Feedback Power Amplifier for 5G Gain Boosting

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Solution Overview

Problem

Two-stage power amplifiers operating in 5G-NR Tx bands face challenges in achieving sufficient gain and wide-band modulation bandwidth due to transistor device parasitics, particularly in envelope tracking mode, limiting their effectiveness in RF communication systems.

Innovation Solution

A power amplifier design incorporating RF-coupled feedback with inductive coupling units between stages, including a first amplification stage with a bipolar transistor and a second stage in push-pull arrangement, along with RF-coupled feedback paths to enhance gain and support wide-band modulation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If two-stage power amplifier is used in 5G-NR Tx bands, then operational frequency is increased, but power gain becomes insufficient due to transistor parasitics

Engineering Contradiction:

Improveoperational frequencyVSAvoidpower gain

Core Design Contradiction:

SpeedVSPower

Solution Approach 1:

The patent introduces an RF-coupled feedback path that feeds a portion of the output signal from the second amplification stage back to the input of the first amplification stage. This feedback mechanism compensates for the gain loss caused by transistor parasitics at high frequencies, thereby maintaining sufficient power gain while operating in 5G-NR bands.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent modifies the feedback coupling method by using RF-coupled feedback instead of conventional DC-coupled feedback. This parameter change in the feedback path allows the system to achieve both high-frequency operation and adequate gain by properly managing the feedback signal coupling at RF frequencies.

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If envelope tracking mode is used, then power efficiency is improved, but gain is further limited due to operation in gain compressed region

Engineering Contradiction:

Improvepower efficiencyVSAvoidpower gain

Core Design Contradiction:

Use of energy by moving objectVSPower

Solution Approach 1:

The RF-coupled feedback path provides additional gain compensation specifically needed when the power amplifier operates in the gain compressed region during envelope tracking mode. The feedback signal helps restore the overall gain while the amplifier operates efficiently in compression.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent combines multiple amplification stages with different characteristics - the first stage operates in linear region providing baseline gain, while the second stage operates in gain compressed region for efficiency. The RF-coupled feedback integrates these stages to achieve both efficiency and sufficient overall gain.

Inventive Principle:

Principle #40Composite materials

3Power

If DC-coupled feedback is used to boost gain, then gain is increased, but memory issues occur

Engineering Contradiction:

ImprovegainVSAvoidmemory effects

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent replaces DC-coupled feedback (electrical coupling) with RF-coupled feedback using inductive coupling. This substitution changes the coupling mechanism from direct electrical connection to magnetic field-based coupling, which provides gain boosting while avoiding the memory effects associated with DC coupling.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Speed

If transistor parasitics are present at high frequency, then frequency operation is enabled, but gain is fundamentally limited

Engineering Contradiction:

Improveoperational frequencyVSAvoidavailable gain

Core Design Contradiction:

SpeedVSPower

Solution Approach 1:

The RF-coupled feedback path compensates for the gain loss caused by transistor parasitics at high frequencies by feeding back a portion of the output signal. This feedback mechanism effectively counteracts the detrimental effects of parasitic capacitance and inductance that limit gain at 5G-NR frequency bands.

Inventive Principle:

Principle #23Feedback

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 design achieves improved gain and modulation bandwidth, particularly in envelope tracking mode, addressing the limitations of existing power amplifiers in 5G-NR Tx bands.

Implementation Method 1

the first and the third coupling units are inductively or RF coupled

Methodology Applied

Scientific EffectInductive coupling: Electromagnetic Induction

Implementation Method 2

The first and second coupling units from an inter-stage balun between the first and second amplification stage to convert a single-ended first amplification stage signal into a differential signal

Methodology Applied

Scientific EffectElectromagnetic coupling: Electromagnetic Induction

Implementation Method 3

featuring capacitors in the feedback path to mitigate parasitic capacitance

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS12531527B2Gain boosting in power amplifiers using RF-coupled feedback

Publication Date: 2026.01.20 SKYWORKS SOLUTIONS INC

AI summary

A power amplifier comprises a first amplification stage having an input terminal receiving a radio frequency (RF) signal to be amplified and having a first coupling unit, a second amplification stage outputting an amplified radio frequency signal and having a second coupling unit and a third coupling unit providing RF feedback to the input terminal of the first amplification stage through an RF feedback path, the second coupling unit being coupled to the first coupling unit, and the third coupling unit being coupled to the first coupling unit.