Trap Filter With Coupled Inductors for Wide Stopband
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Solution Overview
Problem
Conventional trap filters in RF circuits have a narrow stopband due to their large reactance change near resonant frequencies, leading to complex and large circuit configurations when trying to widen the stopband.
Innovation Solution
A trap filter configuration using subtractive-polarity coupled inductors and a capacitor, where the second inductor's inductance is less than the absolute value of mutual inductance, creating negative mutual inductance and a wider frequency range with near-zero reactance, allowing for a wider stopband without increasing the circuit complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple LC parallel resonant circuit is used to create a trap filter, then the circuit configuration remains simple, but the stopband becomes narrow due to large reactance change near resonant frequency
Solution Approach 1:
The single inductor is segmented into two coupled inductors (first inductor and second inductor) with subtractive polarity coupling. This segmentation allows the creation of multiple resonant frequencies through the interaction between the inductors and capacitor, thereby widening the stopband while maintaining circuit simplicity.
Solution Approach 2:
The patent uses composite inductance structure formed by coupling two inductors with subtractive polarity. The combined inductance effect creates negative mutual inductance characteristics that modify the reactance-frequency relationship, enabling wider stopband without proportionally increasing circuit complexity.
2Reliability
If multiple trap filters with different stopbands are combined to widen the stopband, then the stopband width increases, but the circuit configuration becomes complicated and larger in size
Solution Approach 1:
Instead of combining multiple separate trap filters, the patent merges the functions of multiple filters into a single integrated circuit structure using two coupled inductors and one capacitor. The subtractive polarity coupling between inductors creates multiple resonant modes that collectively provide a wide stopband, eliminating the need for multiple discrete filter units.
Solution Approach 2:
The coupled inductor structure performs multiple functions simultaneously: it provides impedance transformation, creates multiple resonant frequencies for wide stopband coverage, and maintains compact size. This multi-functionality replaces what would otherwise require multiple separate trap filter circuits.
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 achieves a wider stopband with moderate reactance change to frequency changes, reducing circuit size and complexity while maintaining effective signal attenuation across a broader frequency range.
Implementation Method 1
The first inductor and the second inductor are subtractive-polarity coupled (coupled to generate negative mutual inductance)
Implementation Method 2
a series LC circuit including an inductor defined by the mutual inductance and the capacitor, and the composite inductance of the second inductor and an inductor defined by the negative mutual inductance resonate in parallel
Data Source
AI summary
A trap filter includes a first inductor, a second inductor, and a capacitor. A first end of the first inductor extends to a first connection portion, a third end of the second inductor is connected to a second end of the first inductor, and a fourth end extends to a second connection portion. The capacitor is connected in parallel with the second inductor. The first inductor and the second inductor are subtractive-polarity coupled. An inductance value of the second inductor is less than an absolute value of mutual inductance generated by coupling of the first inductor and the second inductor.