Low-pass filter with third-path capacitor for independent tuning

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Solution Overview

Problem

Existing low-pass filters composed of LC filters face difficulties in adjusting characteristics to meet performance requirements, as changing capacitance affects both insertion loss and return loss characteristics simultaneously, making it challenging to achieve desired performance characteristics.

Innovation Solution

The low-pass filter design includes a third path with lower inductance than the first and second paths, allowing the capacitance of the third-path capacitor to be adjusted independently to change the reflection characteristic without significantly altering the attenuation characteristic, facilitating easier characteristic adjustments.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the capacitance of the first to third capacitors is adjusted to change the reflection characteristic, then the return loss in the pass band is improved, but the attenuation characteristic in the stop band deteriorates

Engineering Contradiction:

Improvereturn lossVSAvoidattenuation characteristic

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent divides the capacitor adjustment function into separate segments: the first and second capacitors control the attenuation characteristic, while the third capacitor controls the reflection characteristic. This segmentation allows independent adjustment of each characteristic without affecting the other, resolving the technical contradiction between improving return loss and maintaining attenuation characteristic.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a switchable configuration where the third capacitor can be dynamically connected or disconnected. When connected, it adjusts the reflection characteristic; when disconnected, it minimally affects the attenuation characteristic. This dynamic control enables selective optimization of different performance characteristics.

Inventive Principle:

Principle #15Dynamics

2Reliability

If the capacitance of the first to third capacitors is adjusted to change the attenuation characteristic, then the insertion loss in the stop band is improved, but the reflection characteristic in the pass band deteriorates

Engineering Contradiction:

Improveattenuation characteristicVSAvoidreturn loss

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent segments the control functions by assigning the first and second capacitors to control attenuation characteristic and the third capacitor to control reflection characteristic. This allows independent optimization of each characteristic without mutual interference.

Inventive Principle:

Principle #1Segmentation

3Adaptability or versatility

If the inductance of the third path is made lower than the first and second paths, then the independence of adjustment between reflection and attenuation characteristics is improved, but the device complexity increases

Engineering Contradiction:

Improveadjustment independenceVSAvoidpath configuration

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent applies local quality by making the third path distinct from the first and second paths specifically in terms of inductance value. The third path has lower inductance to create a different resonance characteristic, enabling independent control of reflection characteristic without significantly affecting attenuation characteristic.

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 design enables independent adjustment of reflection and attenuation characteristics, allowing for precise tuning of the filter's performance to meet specific requirements without compromising other characteristics.

Implementation Method 1

a first LC parallel resonator and a second LC parallel resonator connected in series and provided between the first input/output port and the second input/output port

Methodology Applied

Scientific EffectResonance: Resonance

Implementation Method 2

The third path includes a third-path capacitor and connects a connection point between the first and second LC parallel resonators to the ground

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 3

The third path has an inductance lower than an inductance of each of the first path and the second path

Methodology Applied

Scientific EffectElectromagnetic Induction: Electromagnetic Induction

Data Source

PatentUS10461716B2Low-pass filter

Publication Date: 2019.10.29 TDK CORP

AI summary

A low-pass filter includes first and second input/output ports, first and second LC parallel resonators connected in series and provided between the first and second input/output ports, and first to third paths. The first path includes a first LC series resonator and connects a first end of the first LC parallel resonator closest to the first input/output port to a ground. The second path includes a second LC series resonator and connects a second end of the second LC parallel resonator closest to the second input/output port to the ground. The third path includes a third-path capacitor and connects a connection point between the first and second LC parallel resonators to the ground.