Filter Circuit Parasitic Inductance Compensation

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Solution Overview

Problem

Conventional filter circuits with multilayer chip varistors suffer from deteriorated high-frequency attenuation characteristics due to parasitic inductance components.

Innovation Solution

Incorporating first and second varistors, coils, and a resistance in a filter circuit configuration where the coils are connected in series with the input and output lines, compensating for the parasitic inductance and improving high-frequency attenuation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a multilayer chip varistor is used as a conventional filter device, then the high-frequency noise attenuation is achieved through capacitance component, but the parasitic inductance component deteriorates the attenuation characteristic at high frequencies

Engineering Contradiction:

Improveattenuation characteristicVSAvoidparasitic inductance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful parasitic inductance into a beneficial feature by intentionally designing coil structures with inductance values. These coils are specifically configured to provide inductive reactance that counteracts the capacitive reactance of the varistor at high frequencies, transforming the previously harmful inductance effect into a useful mechanism for improving attenuation characteristics.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the electrical parameters of the filter circuit by introducing coils with specific inductance values and configuring them in series with the varistor. This parameter modification allows the circuit to achieve better high-frequency attenuation by creating a resonant circuit where the inductive and capacitive reactances interact to enhance noise suppression at targeted frequency ranges.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If coils are added to compensate for parasitic inductance, then high-frequency attenuation is improved, but device complexity increases

Engineering Contradiction:

Improvehigh-frequency attenuationVSAvoidcircuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the coil structures with the existing varistor package by integrating them into a unified filter device. The coils are positioned and configured to work synergistically with the varistor, combining multiple functional elements into a single integrated component that achieves improved high-frequency attenuation without requiring separate discrete components.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent designs the filter device to serve multiple functions: the varistor provides both its traditional surge protection function and capacitance for noise filtering, while the coils provide inductance for high-frequency attenuation. This multi-functionality allows a single device to address multiple electrical protection and filtering needs, reducing the overall system complexity despite the enhanced internal structure.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

Enhances the attenuation characteristic of high frequencies by compensating for the parasitic inductance, resulting in improved frequency performance.

Implementation Method 1

a varistor layer exhibiting a nonlinear current-voltage characteristic

Methodology Applied

Scientific EffectNonlinear current-voltage characteristic:

Implementation Method 2

the filter device attenuates high-frequency noises by the capacitance component of the varistor part

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 3

first and second inner conductors forming a coil... the coils are connected in series with input and output lines, whereby an attenuation effect is obtained at high frequencies

Methodology Applied

Scientific EffectInductance: Inductor

Data Source

PatentUS7646578B2Filter circuit and filter device

Publication Date: 2010.01.12 TDK CORP

AI summary

A filter circuit has first and second varistors, a resistance, an input terminal, an output terminal, and a ground terminal. The resistance is connected between the first and second varistors. The input terminal is connected to a junction between the first varistor and resistance through a first coil. The output terminal is connected to a junction between the second varistor and resistance through a second coil. The ground terminal is connected to a side of the first varistor opposite from the resistance and a side of the second varistor opposite from the resistance.