RF Switch Non-Linearity Compensation Using Harmonic Cancellation

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Solution Overview

Problem

Radio-frequency (RF) switches, particularly those using field-effect transistors (FETs), face challenges in maintaining linearity, which leads to intermodulation distortion and increased susceptibility to interference, affecting the integrity and quality of RF signals.

Innovation Solution

Incorporating a non-linear capacitor, such as a metal-oxide-semiconductor (MOS) capacitor, connected to the source or drain of the FET, which generates harmonics to cancel out non-linearity effects, and utilizing a body bias signal to control these harmonics, along with gate and body bias circuits to improve switching performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional FET is used in an RF switch, then the device structure is simple, but intermodulation distortion increases and linearity deteriorates

Engineering Contradiction:

ImprovelinearityVSAvoiddevice structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

A non-linear capacitor is introduced as an intermediary component connected to the source or drain of the FET. This capacitor generates harmonics that act as a mediator to cancel the non-linearity effects produced by the FET, thereby improving linearity without fundamentally changing the FET structure itself

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent creates a composite switching device by combining the FET with a non-linear capacitor (such as a MOS capacitor). This composite structure leverages the complementary characteristics of both components: the FET provides switching functionality while the non-linear capacitor provides linearity compensation through harmonic generation

Inventive Principle:

Principle #40Composite materials

2Ease of operation

If FET biasing circuits are added to improve switching performance, then switching performance improves, but device complexity increases

Engineering Contradiction:

Improveswitching performanceVSAvoidcircuit complexity

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The non-linear capacitor serves multiple functions simultaneously: it compensates for FET non-linearity, generates harmonics for cancellation, and can be controlled through body bias signals. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby limiting the increase in overall device complexity

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Power

If multiple FETs are connected in series to handle higher power, then power handling capability improves, but device complexity and non-linearity effects increase

Engineering Contradiction:

Improvepower handling capabilityVSAvoiddevice structure

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

Instead of uniformly treating all FETs in the series connection, the patent applies non-linear capacitors selectively to specific FETs (such as those experiencing the most significant non-linearity effects). This localized approach compensates for non-linearity where it matters most while avoiding the complexity of adding components to every FET in the series

Inventive Principle:

Principle #3Local quality

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 significantly reduces intermodulation distortion, enhances linearity, and improves power handling capabilities, leading to better RF signal transmission and reception in multi-band and multi-mode wireless communication systems.

Implementation Method 1

The non-linear capacitor can include a metal-oxide-semiconductor (MOS) capacitor. The MOS capacitor can be configured to generate one or more harmonics to substantially cancel the non-linearity effect generated by the FET.

Methodology Applied

Scientific EffectHarmonic generation:

Implementation Method 2

The one or more harmonics generated by the MOS capacitor can be controlled at least in part by a body bias signal provided to the FET structure of the MOS capacitor.

Methodology Applied

Scientific EffectBody bias control:

Data Source

PatentUS9590614B2Non-linearity compensation in radio frequency switches and devices

Publication Date: 2017.03.07 SKYWORKS SOLUTIONS INC

AI summary

Radio frequency (RF) switches and devices provide improved switching performance. An RF switch includes at least one field-effect transistor (FET) disposed between a first node and a second node, each of the at least one FET having a respective source, drain, gate, and body, and a compensation circuit connected to the respective drain of the at least one FET that compensates a non-linearity effect generated by the at least one FET.