Magnetically Coupled Low-Pass Filter for Low Loss and Stopband Attenuation
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Solution Overview
Problem
Existing filter circuits face challenges in achieving high attenuation in stop frequency bands while minimizing insertion loss in pass frequency bands, and in maintaining impedance matching over a wide band, due to increased inductance requirements.
Innovation Solution
The proposed filter circuit design includes a configuration with magnetic-field-coupled inductors and capacitors, forming parallel and series resonant circuits, which allows for adjustable inductance and capacitance to set resonant frequencies within specific bands, reducing insertion loss and enhancing attenuation in stop frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inductance of the inductive reactance circuit is increased to increase attenuation in the stop frequency band, then the attenuation is improved, but the reactance change with respect to frequency change is increased in the pass frequency band, making it difficult to achieve impedance matching over a wide band and increasing insertion loss
Solution Approach 1:
The inductive reactance circuit is divided into two separate inductors (first inductor and second inductor) with different inductance values. The first inductor has a larger inductance to provide attenuation in the stop band, while the second inductor has a smaller inductance to maintain impedance matching in the pass band. This segmentation allows each inductor to optimize for its specific frequency range without compromising the other.
Solution Approach 2:
Different inductors are assigned different inductance values to optimize performance in different frequency regions. The first inductor (larger inductance) is optimized for stop band attenuation, while the second inductor (smaller inductance) is optimized for pass band impedance matching. This local optimization of component properties resolves the contradiction between attenuation and insertion loss.
2Reliability
If the inductance of the inductive reactance circuit is increased to increase attenuation in the stop frequency band, then the attenuation is improved, but the reactance change with respect to frequency change is increased, making it difficult to achieve impedance matching over a wide band
Solution Approach 1:
The inductive reactance circuit is segmented into two inductors with different inductance values to handle different frequency ranges. The first inductor provides the necessary reactance for stop band rejection, while the second inductor maintains appropriate reactance levels in the pass band, enabling wideband impedance matching.
Solution Approach 2:
The inductance parameter is varied across different components (first inductor has larger inductance, second inductor has smaller inductance) to optimize performance across different frequency ranges. This parameter variation allows the circuit to achieve both high attenuation in the stop band and wide impedance matching bandwidth in the pass band.
3Reliability
If the inductance of the shunt-connected inductive reactance circuit is made small to increase attenuation in the stop frequency band, then the attenuation is improved, but the reactance in the pass frequency band becomes small, increasing the insertion loss
Solution Approach 1:
The inductive reactance circuit is segmented into series and shunt components with different inductance values. The series inductor (first inductor) has larger inductance for stop band attenuation, while the shunt inductor (second inductor) has smaller inductance to maintain proper reactance in the pass band, preventing excessive insertion loss.
Solution Approach 2:
Different inductance values are assigned to series and shunt inductors based on their specific functional requirements. The series inductor is optimized for attenuation, while the shunt inductor is optimized for maintaining pass band performance. This local quality differentiation resolves the contradiction between attenuation and insertion loss.
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 effectively reduces insertion loss in pass frequency bands and increases attenuation in stop frequency bands, while maintaining impedance matching across a wide range, thereby improving the performance of low and high pass filters.
Implementation Method 1
a second inductor electrically connected between a node between the first inductor and the second port, and the ground terminal, and magnetic-field-coupled to the first inductor
Implementation Method 2
the first inductor and the second inductor are additive-polarity-coupled to each other
Implementation Method 3
a first capacitor electrically connected in parallel to the third inductor and defining a first parallel resonant circuit together with the third inductor
Data Source
AI summary
A low pass filter includes a first inductor, a second inductor magnetic-field-coupled to the first inductor, a third inductor, and a first capacitor. The first inductor is electrically connected between a first port and an intermediate node, being a node to which the second inductor is electrically connected, between the first inductor and the second port. The second inductor is electrically connected between the intermediate node and a ground terminal. The third inductor is electrically connected between the intermediate node and the second port, and a first parallel resonant circuit is defined by the third inductor and the first capacitor. The first inductor and the second inductor are coupled to each other in such a relationship that a negative inductance is generated between the intermediate node and the third inductor due to magnetic field coupling between the first inductor and the second inductor.