Doherty Amplifier Phase Compensation for Group Delay Matching

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Solution Overview

Problem

Doherty amplifiers face efficiency losses due to phase coherency issues between main and peaking amplifier paths, leading to non-ideal load modulation and reduced peak power capability across the full operational band, especially at high power levels.

Innovation Solution

Incorporating passive phase and delay compensation circuits in the main and peaking input paths of Doherty amplifiers, utilizing transmission line-based series delay elements and shunt 90-degree short-circuit stubs to equalize group delays and optimize load impedance dispersion, thereby enhancing phase coherency and efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If passive phase compensation circuits are added to equalize group delays, then phase coherency and efficiency are improved, but device complexity increases

Engineering Contradiction:

Improvephase coherencyVSAvoidcircuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

A passive phase compensation circuit is introduced as an intermediary element between the power splitter and the amplifiers. This circuit includes a first phase compensation network in the main amplifier path and a second phase compensation network in the peaking amplifier path, which equalize the group delays of both paths without requiring active control mechanisms.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent employs identical or matched passive phase compensation networks in both the main and peaking amplifier paths. By copying the same circuit topology and component values in both paths, the design achieves symmetry that simplifies analysis and ensures equal group delay compensation while maintaining simplicity.

Inventive Principle:

Principle #26Copying

2Manufacturing precision

If transmission line-based delay elements and stubs are used for phase compensation, then manufacturing precision is improved, but device complexity increases

Engineering Contradiction:

Improvephase delay accuracyVSAvoidcircuit structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent replaces active electronic phase control mechanisms with passive transmission line-based phase compensation networks. These networks use distributed electrical elements (transmission lines and stubs) rather than active components, providing stable and predictable phase delay characteristics that are determined by physical dimensions and characteristic impedances, thereby improving manufacturing precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent achieves precise phase delay control by carefully selecting and adjusting the physical parameters of the transmission lines, including their lengths, characteristic impedances, and stub dimensions. By optimizing these parameters during the design phase, the circuit achieves accurate group delay equalization without requiring complex active control systems.

Inventive Principle:

Principle #35Parameter changes

3Use of energy by moving object

If phase compensation circuits are implemented, then efficiency at back-off levels is improved, but loss of energy increases due to additional circuit elements

Engineering Contradiction:

Improveefficiency at back-offVSAvoidcircuit losses

Core Design Contradiction:

Use of energy by moving objectVSLoss of energy

Solution Approach 1:

The patent employs simple, passive, and loss-minimized circuit elements (transmission lines and short-circuit stubs) that can be easily fabricated as part of the amplifier assembly. These elements provide the necessary phase compensation with minimal insertion loss, and their simplicity allows for optimized manufacturing that reduces overall energy losses in the compensation networks.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 compensation circuits improve the utilization of Doherty power amplifiers by reducing peak power dispersion and increasing efficiency at fixed output power back-off levels, while minimizing circuit losses and avoiding the complexity of active control circuits.

Implementation Method 1

utilizing transmission line-based series delay elements and shunt 90-degree short-circuit stubs to equalize group delays

Methodology Applied

Scientific EffectElectromagnetic wave propagation:

Implementation Method 2

shunt 90-degree short-circuit stubs to equalize group delays

Methodology Applied

Scientific EffectElectromagnetic reflection: Reflection

Data Source

PatentUS10630242B2Doherty amplifiers with passive phase compensation circuits

Publication Date: 2020.04.21 NXP USA INC

AI summary

A Doherty amplifier has a first amplifier path that includes a first amplifier, a second amplifier path that includes a second amplifier, a power divider, and a short-circuited stub. The power divider receives an RF signal and divides the RF signal into first and second input signals. The power divider includes first and second power divider outputs that produce the first and second input signals, respectively. The short-circuited stub is coupled between the first power divider output and the first amplifier or between the second power divider output and the second amplifier. The first and second amplifier paths are characterized by first and second frequency-dependent insertion phases, respectively. A slope of the first or second frequency-dependent insertion phase is altered by the short-circuited stub. The power divider produces the first and second input signals with a quadrature phase shift.