Frequency-Variable LC Filter Topology for Steep Bandpass Attenuation
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Solution Overview
Problem
Existing frequency-variable LC filters require multiple variable capacitors, leading to increased circuit size and loss of bandpass characteristics, with uneven steepness of attenuation characteristics at low and high frequency sides.
Innovation Solution
A frequency-variable LC filter design with a simplified configuration using fewer variable capacitors, where the first series arm LC filter circuit includes a fixed capacitor and an LC series circuit, and the parallel arm LC filter circuits have variable capacitors and inductors, allowing for adjustable resonant frequencies and improved attenuation characteristics across the pass band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple variable capacitors are used to adjust bandpass characteristics, then the filter can provide frequency variability, but the circuit size increases
Solution Approach 1:
The patent merges the functions of multiple variable capacitors into a single variable capacitor that controls the resonant frequency of the LC circuit. By combining the frequency adjustment function that previously required multiple capacitors into one component, the circuit size is reduced while maintaining frequency variability through the resonant frequency adjustment mechanism.
2Device complexity
If variable capacitors are connected in series between input and output terminals, then the filter configuration is established, but the loss of bandpass characteristics increases
Solution Approach 1:
The patent extracts the variable capacitors from the series connection between input and output terminals and repositions them within the LC resonant circuit structure. Specifically, the variable capacitor is integrated into the parallel LC circuit where it adjusts the resonant frequency without being in the direct signal path between input and output, thereby reducing loss of bandpass characteristics while maintaining the necessary filter configuration.
3Adaptability or versatility
If the filter configuration uses multiple variable capacitors in series, then frequency adjustment is achieved, but the steepness of attenuation characteristics becomes uneven
Solution Approach 1:
The patent applies local quality by positioning the variable capacitor specifically within the parallel LC circuit rather than in series between terminals. This localized placement allows the variable capacitor to effectively adjust the resonant frequency and influence both low and high frequency attenuation characteristics uniformly, creating balanced steepness on both sides of the pass band while maintaining frequency adjustment capability.
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
The design achieves steep attenuation characteristics at both sides of the pass band with reduced loss and enlarged frequency range, maintaining desired bandpass characteristics and attenuations, even when the pass band is changed.
Implementation Method 1
a frequency-variable LC filter including a resonance circuit of an inductor and a variable capacitor
Implementation Method 2
The first series arm LC filter circuit includes a fixed capacitor, an LC series circuit, and an LC parallel circuit
Data Source
AI summary
A first series arm LC filter circuit includes a capacitor and an inductor connected in series to provide a series circuit between a first connection terminal and a second connection terminal, a capacitor connected in parallel to the series circuit, and an inductor and a variable capacitor connected in parallel between a connection point of the capacitor and the inductor and a ground potential. A first parallel arm LC filter circuit is connected between the first connection terminal and the ground potential. A second parallel arm LC filter circuit is connected between the second connection terminal and the ground potential. The inductor is directly connected to the second connection terminal or is connected to the second connection terminal with another inductor interposed therebetween.