Variable-Impedance Resonant Circuit for Tunable RF Filters
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Solution Overview
Problem
Current radiofrequency filters in telecommunications systems are inflexible due to their fixed center frequency and bandwidth, requiring multiple components for different standards and geographic regions, leading to increased complexity and cost.
Innovation Solution
A resonant circuit with stabilized characteristic impedance, comprising a group of piezoelectric resonators and variable impedance matching elements, allows for adjustable central frequency and bandwidth while maintaining impedance matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple fixed-frequency filters are used to support multiple communication standards, then frequency coverage is improved, but device complexity increases
Solution Approach 1:
The patent implements a single resonant circuit that can be electronically reconfigured to function as multiple different filters with varying center frequencies and bandwidths. By using a group of piezoelectric resonators with adjustable impedance matching elements, the circuit universally handles multiple communication standards (WCDMA, LTE, NR) without requiring separate physical filters for each standard, thus reducing component count while maintaining broad frequency coverage
Solution Approach 2:
The patent employs dynamically adjustable impedance matching elements (variable capacitors or electronically controlled components) that allow the resonant circuit's characteristics to be changed in real-time. This dynamic reconfiguration enables the same hardware to adapt to different frequency bands and bandwidth requirements, transforming a static filter into a versatile, reconfigurable component that reduces the need for multiple fixed-frequency filters
2Adaptability or versatility
If impedance matching elements are made variable to adjust frequency and bandwidth, then adaptability is improved, but stability of characteristic impedance deteriorates
Solution Approach 1:
The patent incorporates control means that monitor and adjust the impedance matching elements to maintain a stable characteristic impedance (e.g., 50 ohms) across different operating conditions. The control system receives feedback about the current impedance state and dynamically adjusts the variable elements to compensate for changes, ensuring that the filter maintains proper impedance matching to the signal source and load despite frequency and bandwidth variations
Solution Approach 2:
The patent carefully manages the parameters of the impedance matching elements (such as capacitance values) to achieve frequency and bandwidth adjustment while maintaining characteristic impedance stability. By selecting specific parameter ranges and adjustment steps for the variable elements, the system enables tunability without allowing the characteristic impedance to drift significantly, thus resolving the conflict between adaptability and impedance stability
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
Enables the production of filters with variable central frequency and bandwidth, reducing the number of components needed and improving frequency coverage across multiple bands, from 700 MHz to 900 MHz, covering 25% of the frequency spectrum.
Implementation Method 1
a group of N piezoelectric resonators with N>1, said resonators having the same resonant frequency and the same antiresonant frequency
Implementation Method 2
resonant circuit with stabilized characteristic impedance comprising an input terminal (Pe) and an output terminal (Ps) and at least: a group of N piezoelectric resonators with N>1, said resonators having the same resonant frequency and the same antiresonant frequency
Data Source
Figure 1a~1c
Figure 2~3
Figure 4~5a
AI summary
The subject of the invention is a resonant circuit comprising an input terminal (Pe) and an output terminal (Ps) and at least: - a group of N resonators with N ≥1, having the same resonant frequency and the same antiresonance frequency; - first and second impedance matching elements (Cs, Cp) having a non-zero reactance, the first element being in series with said group of resonators, and the second element being in parallel with said group of resonators said circuit resonator comprising: - first control means of said group of resonators making it possible to fix the static capacitance (C0) of said group at a first value; - second control means making it possible to fix the impedance of the first element and that of the second element at second values; said first and second values being such that: the triplet of values: static capacitance of said group/impedance of the first element/impedance of the second element (C0, Cs, Cp) makes it possible to determine the following triplet of parameters: o the characteristic impedance Zc of the assembly consisting of said group, said first impedance matching element and said second matching element; o the resonance frequency ωr of said set; o the antiresonance frequency ωa of said assembly, to stabilize the impedance of said circuit at a chosen characteristic impedance.