RF Amplifier Balun-Transformer Topology for Low-Loss Doherty Combining

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Solution Overview

Problem

Conventional RF amplifiers face challenges in achieving high efficiency amplification with low loss, particularly in applications requiring beamforming and millimeter wave frequencies, due to the use of lossy and space-consuming coupled-line baluns.

Innovation Solution

The implementation of an RF amplifier with a differential balun combiner and a transformer component, which uses lumped element components to achieve impedance transformation, allowing for efficient power combination and reduced loss, and incorporates a quarter wave length transformer for proper Doherty operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If coupled-line baluns are used for impedance transformation in RF amplifiers, then impedance matching can be achieved, but the system suffers from high loss, narrow bandwidth, and large size

Engineering Contradiction:

Improvepower lossVSAvoidbandwidth

Core Design Contradiction:

Loss of energyVSAdaptability or versatility

Solution Approach 1:

The patent replaces the conventional coupled-line balun (transmission line-based mechanical structure) with an active impedance transformation circuit implemented using transistors and resistors. This substitution eliminates the inherent losses and bandwidth limitations of coupled-line structures while achieving the same impedance matching function through active electronic components, thereby reducing power loss and expanding operational bandwidth.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the fundamental operating parameters by transitioning from passive transmission line-based impedance transformation to active solid-state circuit implementation. This parameter change enables broadband operation and reduced loss by utilizing the frequency-independent characteristics of active components compared to the frequency-dependent behavior of coupled-line structures.

Inventive Principle:

Principle #35Parameter changes

2Area of stationary object

If conventional baluns are used in RF amplifiers, then impedance transformation is provided, but the device occupies large space and has limited bandwidth

Engineering Contradiction:

Improvecircuit board areaVSAvoidbandwidth

Core Design Contradiction:

Area of stationary objectVSAdaptability or versatility

Solution Approach 1:

The patent substitutes the physical coupled-line balun structure with an active impedance transformation circuit using standard semiconductor components. This replacement dramatically reduces the required circuit board area while simultaneously providing broadband operation, as active components are not constrained by the physical length and coupling geometry requirements of transmission line structures.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Loss of energy

If coupled-line baluns are used for power combination, then signal combining can be achieved, but the system experiences high loss and narrow bandwidth

Engineering Contradiction:

Improvecombination lossVSAvoidbandwidth

Core Design Contradiction:

Loss of energyVSDuration of action of moving object

Solution Approach 1:

The patent replaces the coupled-line balun-based power combining approach with active impedance transformation circuits that enable broadband power combination with reduced loss. The active circuitry maintains signal integrity across a wide frequency range while minimizing power dissipation, overcoming the inherent limitations of transmission line-based combining networks.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

This configuration provides high efficiency amplification with low loss, suitable for millimeter wave frequencies, and enables compact design by eliminating the need for coupled-line baluns, thereby enhancing performance and reducing space requirements.

Implementation Method 1

The transformer component can provide the impedance transformation operation needed for proper Doherty operation

Methodology Applied

Scientific EffectImpedance transformation: Electromagnetic Induction

Implementation Method 2

a first differential balun combiner configured to provide a first single-ended RF signal to the output node based on combining a first differential RF signal

Methodology Applied

Scientific EffectElectromagnetic coupling: Electromagnetic Induction

Data Source

PatentUS12603622B2Apparatus and methods for radio frequency amplifiers

Publication Date: 2026.04.14 ANALOG DEVICES INT UNLTD CO

AI summary

Apparatus and methods for radio frequency (RF) amplification are disclosed. In certain embodiments, an RF amplifier includes an output node configured to output an RF output signal, a main amplifier stage including a differential output, a first differential balun combiner configured to provide a first single-ended RF signal to the output node based on combining a first differential RF signal from the differential output of the main amplifier stage, an auxiliary amplifier stage including a differential output, a transformer component, and a second differential balun combiner configured to generate a second single-ended RF signal based on combining a second differential RF signal from the differential output of the auxiliary amplifier stage. The second differential balun combiner provides the second single-ended RF signal to the output node through the transformer component.