Variable Filter Circuit Steep Attenuation via Inductor
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Solution Overview
Problem
Existing variable filter circuits face challenges in achieving steep attenuation characteristics near the lower frequency side of the pass band, leading to increased circuit size and complexity due to the need for multiple variable capacitors and resonators.
Innovation Solution
A variable filter circuit design incorporating a first inductor in parallel with a resonator and variable capacitors in series arms, allowing for adjustable attenuation characteristics by controlling inductance and capacitance, which reduces the number of required capacitors and simplifies the control system while maintaining steepness near the lower frequency side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two variable capacitors are connected to a single resonator to make the frequencies in the pass band variable, then the pass band can be adjusted, but the total number of variable capacitors increases and the circuit size and control system become complicated
Solution Approach 1:
The patent extracts the frequency adjustment function from the variable capacitors and implements it through digital signal processing in the baseband. Instead of using multiple variable capacitors to adjust pass band frequencies, the invention uses a single resonator with fixed capacitance and achieves frequency selectivity through digital filtering, thereby reducing circuit complexity while maintaining pass band adjustability
Solution Approach 2:
The patent replaces the mechanical/electrical variable capacitor system with a digital signal processing system. The physical variable capacitors that required manual or electronic adjustment are substituted with digital filters that can be programmed to adjust pass band characteristics, thereby reducing the number of physical components and simplifying the control system
2Reliability
If multiple variable capacitors are used to achieve desired attenuation characteristics, then the attenuation characteristics can be improved, but the circuit size increases
Solution Approach 1:
The patent combines the functions of multiple variable capacitors and resonators into a single resonator with digital signal processing. The attenuation characteristics that previously required multiple separate components are achieved through a unified architecture where one resonator works in conjunction with digital filters, thereby reducing circuit size while maintaining or improving attenuation performance
Solution Approach 2:
The single resonator in the patent serves multiple functions: it provides the primary frequency selectivity, works with the digital filters to achieve attenuation characteristics, and enables pass band adjustment. This multi-functional design replaces what previously required multiple specialized components, reducing overall circuit size while maintaining 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 design achieves steep attenuation characteristics near the lower frequency side with reduced circuit complexity and size, enabling flexible adjustment of cutoff frequencies and supporting multiple communication bands with improved attenuation.
Implementation Method 1
a resonator connected in series between a first input/output terminal and a node
Implementation Method 2
variable capacitors connected in parallel and in series to a resonator
Implementation Method 3
a first inductor connected in series between the node and the ground connection terminal. Then, the attenuation characteristics that are steep in the vicinity of the lower frequency side in the pass band are obtainable by appropriately adjusting the inductance of the first inductor
Data Source
AI summary
A variable filter circuit (10) includes a parallel arm (11) connected between a port (P3) and node (A), a series arm (12) including a resonator (Re_s1) connected in series between a port (P1) and node (A), and a series arm (13) including a resonator (Re_s2) connected in series between a port (P2) and node (A). The parallel arm (11) includes a first inductor (Lp1). The series arms (12, 13) include variable capacitors (Cp_s1, Cp_s2) connected in parallel to the resonators (Re_s1, Re_s2).