Unmatched Power Amplifier Baseband Termination Circuit

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Solution Overview

Problem

Power amplifier devices for wireless communication systems lack in-package RF output impedance matching circuitry, resulting in relatively narrow signal bandwidths due to resonance issues with printed circuit board components, which limits their performance and efficiency.

Innovation Solution

Incorporating in-package baseband termination circuitry with series-coupled inductance, resistance, and high-value capacitance between the transistor output and ground reference, effectively isolating the RF path and enabling custom harmonic terminations at the PCB assembly level, thereby enhancing signal bandwidth and baseband frequency responses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If power amplifier devices lack in-package RF output impedance matching circuitry, then device simplicity and custom harmonic termination capability are improved, but signal bandwidth becomes narrow due to resonance of PCB bias line inductance with device and package capacitance

Engineering Contradiction:

Improvecustom harmonic termination capabilityVSAvoidsignal bandwidth

Core Design Contradiction:

Adaptability or versatilityVSProductivity

Solution Approach 1:

An in-package baseband termination circuit is introduced as an intermediary element between the power amplifier output and ground. This circuit includes a baseband inductance in series with a baseband resistance, configured to present low impedance at baseband frequencies and high impedance at RF frequencies. The intermediary circuit effectively isolates the RF path from baseband resonance effects while enabling custom harmonic termination at the PCB level, thus resolving the contradiction between adaptability and signal bandwidth.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If in-package baseband termination circuitry is added to unmatched power amplifier devices, then signal bandwidth and baseband frequency response are improved, but device complexity increases

Engineering Contradiction:

Improvesignal bandwidthVSAvoidin-package circuitry complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The baseband termination circuit utilizes parameter changes in impedance with frequency: at baseband frequencies the circuit presents low impedance (baseband inductance + baseband resistance to ground), while at RF frequencies it presents high impedance. This parameter change approach allows the same circuit structure to simultaneously improve signal bandwidth by preventing baseband resonance and maintain RF performance by isolating the RF path, thereby improving productivity with minimal increase in device complexity.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If PCB bias line inductance resonates with device and package capacitance, then unmatched device simplicity is maintained, but baseband frequency response deteriorates due to resonance effects

Engineering Contradiction:

Improveunmatched device simplicityVSAvoidbaseband frequency response

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The in-package baseband termination circuit acts as an intermediary that prevents resonance between PCB bias line inductance and device/package capacitance. The baseband inductance in series with baseband resistance creates a low-impedance path to ground at baseband frequencies, effectively damping any resonant oscillations. This intermediary circuit maintains device simplicity by being integrated in-package while significantly improving baseband frequency response reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 solution allows for improved baseband frequency responses and increased signal bandwidth, enabling better power amplifier performance and enabling custom harmonic terminations, which can enhance power-added efficiency and peak power capability.

Implementation Method 1

The baseband termination circuit is configured to present a low impedance to signal energy at baseband frequencies and a high impedance to signal energy at RF frequencies

Methodology Applied

Scientific EffectImpedance filtering: Filter (electronic)

Implementation Method 2

Incorporating in-package baseband termination circuitry with series-coupled inductance, resistance, and high-value capacitance between the transistor output and ground reference

Methodology Applied

Scientific EffectSeries RLC circuit resonance: Resonance

Data Source

PatentUS11515847B2Power amplifiers and unmatched power amplifier devices with low baseband impedance terminations

Publication Date: 2022.11.29 NXP USA INC

AI summary

A packaged RF amplifier device includes input and output leads and a transistor die. The transistor die includes a transistor with a drain-source capacitance below 0.1 picofarads per watt. The device also includes a conductive connection between the transistor output terminal and the output lead, and a baseband termination circuit between the transistor output terminal and a ground reference node. The baseband termination circuit presents a low impedance to signal energy at envelope frequencies and a high impedance to signal energy at RF frequencies. The baseband termination circuit includes an inductive element, a resistor, and a capacitor connected in series between the transistor output terminal and the ground reference node. Except for a minimal impedance transformation associated with the conductive connection, the device is unmatched between the transistor output terminal and the output lead by being devoid of impedance matching circuitry between the transistor output terminal and the output lead.