Variable Frequency Filter Circuit With Sharp Attenuation Tuning
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing variable frequency filters require increased circuit size to improve attenuation characteristics, leading to complex configurations that compromise simplicity and effectiveness.
Innovation Solution
A variable frequency filter design incorporating a series arm resonant circuit with a fixed capacitor and two parallel arm resonant circuits, each containing a variable capacitor, inductor, and elastic wave resonator, where the fixed capacitor is connected to the parallel arm with lower impedance, allowing for frequency variation while maintaining sharp attenuation characteristics at both high and low frequency sides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional series arm resonant circuits or parallel arm resonant circuits are connected to improve attenuation characteristics, then the attenuation characteristics are improved, but the circuit size is increased
Solution Approach 1:
The patent changes the electrical parameters (capacitance values, impedance levels) of the existing resonant circuit components to optimize attenuation characteristics without adding more circuits. By adjusting the capacitance of fixed capacitors and variable capacitors, and selecting appropriate impedance levels for parallel arm resonant circuits, the desired attenuation is achieved with the same circuit topology, avoiding circuit size increase.
Solution Approach 2:
The patent applies different impedance characteristics to different parallel arm resonant circuits based on their positions in the ladder structure. Specifically, parallel arm resonant circuits closer to the input terminal have different impedance specifications than those closer to the output terminal, optimizing local attenuation performance without requiring uniform addition of circuits throughout the structure.
2Device complexity
If the configuration is simplified to reduce circuit size, then the circuit complexity is reduced, but the attenuation characteristics deteriorate
Solution Approach 1:
The patent achieves simplified configuration by using a standard ladder structure with carefully selected parameter values. The fixed capacitors and variable capacitors are designed with specific capacitance ratios, and the parallel arm resonant circuits are designed with specific impedance values, allowing the basic ladder topology to deliver superior attenuation without requiring additional complex circuit elements.
Solution Approach 2:
The patent designs the resonant circuits to serve multiple functions simultaneously. Each parallel arm resonant circuit provides both impedance transformation and attenuation at specific frequency bands, while the series arm resonant circuits provide both signal transmission and rejection of unwanted frequencies. This multi-functionality allows compact design without sacrificing performance.
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 configuration enables simple and effective frequency filtering with improved attenuation characteristics across the pass band, allowing for flexible frequency adjustment and reduced circuit complexity.
Implementation Method 1
a variable capacitor, an inductor, and an elastic wave resonator are connected in parallel to each other in the series arm resonant circuit
Implementation Method 2
a variable capacitor, an inductor, and an elastic wave resonator are connected in parallel to each other in the series arm resonant circuit
Implementation Method 3
a variable capacitor, an inductor, and an elastic wave resonator are connected in parallel to each other in the series arm resonant circuit
Data Source
AI summary
A variable frequency filter includes a series arm resonant circuit and first and second parallel arm resonant circuits. The series arm resonant circuit is connected between a first connection terminal and a second connection terminal. The first parallel arm resonant circuit is connected to the first connection terminal side of the series arm resonant circuit. In the first parallel arm resonant circuit, a first piezoelectric resonator and a variable capacitor are connected in series to each other. The second parallel arm resonant circuit is connected to the second connection terminal side of the series arm resonant circuit. In the second parallel arm resonant circuit, a second piezoelectric resonator and a variable capacitor are connected in series to each other. The impedance of the first piezoelectric resonator is lower than the impedance of the second piezoelectric resonator. The series arm resonant circuit includes a characteristic adjusting capacitor at the first connection terminal side.