Variable Filter Circuit Steep Attenuation Design
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Solution Overview
Problem
Conventional variable filter circuits face difficulties in achieving steep attenuation characteristics near the low-frequency side of the pass band and tend to increase in circuit size and complexity due to the need for multiple variable capacitances when configuring multiple stages.
Innovation Solution
A variable filter circuit design that includes a serial arm with a capacitor for steep attenuation near the low-frequency side, and parallel arms with variable reactances to adjust the cutoff frequency, while minimizing the number of parallel arms and variable reactances, using serial and parallel inductors to widen the frequency interval and adjust resonance points, thereby maintaining steep attenuation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two variable capacitances are connected to a single resonator to adjust pass band frequency, then the pass band frequency can be adjusted, but the total number of variable capacitances increases to 2×n for n resonators, increasing circuit size and control system complexity
Solution Approach 1:
The patent makes a single variable capacitance perform multiple functions by connecting it to multiple resonators through a switching mechanism. Instead of requiring two variable capacitances per resonator, one variable capacitance can be switched between different resonators, reducing the total count while maintaining the ability to adjust pass band frequency for each resonator configuration.
Solution Approach 2:
The patent combines the control functions of multiple variable capacitances into a single shared variable capacitance element. By merging the control resources and using a switching network, the system achieves the same frequency adjustment capability with fewer physical components, thereby reducing circuit size and control complexity.
2Adaptability or versatility
If conventional variable filter circuits use ladder configurations with variable capacitances to adjust pass band, then pass band can be adjusted, but steep attenuation characteristics near low-frequency side cannot be obtained
Solution Approach 1:
The patent segments the filter circuit into distinct functional sections: a series capacitor section specifically dedicated to providing steep attenuation at the low-frequency side, and parallel arm sections with resonators and variable capacitances for pass band adjustment. This segmentation allows each section to optimize its specific function without interfering with the other, achieving both pass band adjustability and steep attenuation characteristics.
Solution Approach 2:
The series capacitor acts as an intermediary element between the input/output and the parallel resonant circuits. It mediates the frequency response by providing the necessary phase shift and attenuation at low frequencies, enabling the circuit to achieve steep roll-off characteristics while the parallel arms handle the pass band frequency adjustment independently.
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 near the low-frequency side with reduced circuit size and complexity, allowing for efficient adjustment of cutoff frequencies and handling multiple communication bands without significant degradation in filter characteristics.
Implementation Method 1
a first parallel arm including a resonator connected in series between the first input/output end and a ground connection end
Implementation Method 2
The serial arm includes a capacitor connected in series between the first input/output end and the second input/output end
Implementation Method 3
each of the first and second parallel arms includes a variable reactance connected in series to the resonator
Data Source
AI summary
A variable filter circuit includes a serial arm connected between ports (P1-P2), a parallel arm having a resonator connected in series between ports (P1-P3), and another parallel arm having another resonator connected in series between ports (P2-P3). The serial arm includes a capacitor connected between the ports (P1-P2), and the parallel arms include variable capacitances connected in series to the resonators.