Broadband Power Amplifier Harmonic Termination Circuit

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Solution Overview

Problem

Designing broadband power amplifiers using GaN-based devices is challenging due to low drain-source capacitance and significant efficiency drops caused by high D2 inductance and varying second harmonic terminations across a wide bandwidth.

Innovation Solution

Incorporating a harmonic termination circuit with a series-coupled inductance and capacitance between the transistor output and ground, which effectively increases the drain-source capacitance and reduces D2 inductance, while controlling second harmonic impedance across a wide fractional bandwidth at low impedance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If GaN-based devices are used for broadband power amplification, then power density and efficiency are improved, but drain-source capacitance becomes too low for conventional output impedance matching

Engineering Contradiction:

Improvepower-added efficiencyVSAvoiddrain-source capacitance

Core Design Contradiction:

Loss of energyVSQuantity of substance

Solution Approach 1:

The patent merges the output impedance matching function with a low-pass filter structure. By combining the shunt capacitor with the low-pass filter capacitor and merging the series inductor with the D2 inductance, the circuit achieves both impedance matching and harmonic filtering functions simultaneously, allowing GaN devices with low drain-source capacitance to be effectively utilized for broadband amplification.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The output matching circuit is designed to perform multiple functions: impedance matching across broadband frequencies, harmonic frequency filtering, and video bandwidth control. This multi-functional design enables a single circuit topology to address multiple challenges associated with GaN-based broadband power amplifiers.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If high D2 inductance is used for output impedance matching, then matching is improved, but efficiency drops significantly across wide bandwidth

Engineering Contradiction:

Improveoutput impedance matchVSAvoidefficiency

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent employs dynamic biasing and control mechanisms that allow the D2 inductance and associated circuit elements to adapt their effective values across the operating bandwidth. This dynamic adjustment maintains optimal impedance matching while minimizing efficiency losses at different frequencies within the broadband range.

Inventive Principle:

Principle #15Dynamics

3Device complexity

If conventional output matching circuits are used, then simple design is achieved, but second harmonic impedance varies significantly across wide bandwidth

Engineering Contradiction:

Improvecircuit design simplicityVSAvoidsecond harmonic impedance

Core Design Contradiction:

Device complexityVSStability of the object's composition

Solution Approach 1:

The output matching circuit is segmented into distinct functional sections: a low-pass filter section for harmonic rejection, a shunt capacitor section for impedance matching, and a series inductor section for broadband stabilization. This segmentation allows each section to independently control specific aspects of the impedance profile, maintaining stable second harmonic termination across wide bandwidth.

Inventive Principle:

Principle #1Segmentation

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 approach enhances efficiency and achieves high power-added efficiency for broadband applications by reducing the need for additional inductance in the output impedance matching circuit and stabilizing second harmonic impedance.

Implementation Method 1

Incorporating a harmonic termination circuit with a series-coupled inductance and capacitance between the transistor output and ground, which effectively increases the drain-source capacitance

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

reduces D2 inductance, while controlling second harmonic impedance across a wide fractional bandwidth at low impedance

Methodology Applied

Scientific EffectInductance: Inductor

Implementation Method 3

controlling second harmonic impedance across a wide fractional bandwidth at low impedance

Methodology Applied

Scientific EffectImpedance control:

Data Source

PatentUS10742178B2Broadband power transistor devices and amplifiers and methods of manufacture thereof

Publication Date: 2020.08.11 NXP USA INC

AI summary

Embodiments of RF amplifiers and packaged RF amplifier devices each include a transistor with a drain-source capacitance that is relatively low, an output impedance matching circuit, and a harmonic termination circuit. The impedance matching circuit includes a harmonic termination circuit, which includes a first inductance (a first plurality of bondwires) and a first capacitance coupled in series between the transistor output and a ground reference node. An equivalent capacitance from a combination of the first inductive element and the first capacitance in series effectively increases the drain-source capacitance by at least 10 percent. The impedance matching circuit also includes a second inductance (a second plurality of bondwires) and a second capacitance coupled in series between the transistor output and the ground reference node, where the second inductance and the second capacitance are directly connected. The first and second capacitances may be metal-insulator-metal capacitors in an integrated passive device.