Switchable Dual-Band Filter with Impedance Matching
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Solution Overview
Problem
Conventional switchable or tunable RF filters require large circuit areas and suffer from impedance matching issues when switching between different frequency bands, limiting their effectiveness and size reduction potential.
Innovation Solution
A switchable dual-band filter design that integrates a switch into the resonator elements and employs dual-band impedance conversion circuits to adjust and match impedance at both operating passbands, using an external voltage to switch between frequencies, thereby reducing circuit size and improving matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a filter bank with multiple independent filters is used to achieve switchable passbands, then the filtering response is good, but the circuit area and number of elements increase
Solution Approach 1:
The patent combines multiple filter functions into a single resonator structure by integrating switchable capacitive elements. Instead of using separate filters for different passbands, the invention merges them into one resonator that can be tuned to different frequencies by switching between different capacitor configurations, thereby reducing circuit area while maintaining filtering performance
Solution Approach 2:
The resonator is designed with multi-functionality to operate at multiple passbands. By incorporating switchable capacitive elements, the same resonator structure can serve different filtering functions at different frequencies, eliminating the need for multiple dedicated filters and reducing the overall circuit complexity
2Adaptability or versatility
If the resonance frequency of the resonator element is changed drastically to achieve wide tuning range, then the operating passband range increases, but the impedance matching between terminals and resonator deteriorates
Solution Approach 1:
The patent employs dynamic impedance matching by making the matching elements (capacitors) switchable. As the resonator frequency changes, the matching capacitors can be reconfigured to maintain optimal impedance matching between the input/output terminals and the resonator across different passbands, thereby preserving reliability over a wide tuning range
Solution Approach 2:
The invention changes the electrical parameters of the matching network in conjunction with the resonator frequency changes. By adjusting the capacitance values of the matching capacitors according to the operating passband, the impedance matching is optimized for each frequency range, allowing wide tunability without sacrificing matching quality
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 solution achieves a compact filter design with proper impedance matching at both operating frequencies, reducing the overall size and circuit complexity while maintaining effective filtering performance.
Implementation Method 1
The varactor diode is an equivalent of a capacitor, whose capacitance depends on the external control voltage. Therefore, the frequency of the resonator element can be changed by changing the external control voltage.
Implementation Method 2
A filter includes a varactor diode inside each resonator element of the filter. The frequency of the resonator element can be changed by changing the external control voltage.
Data Source
AI summary
A switchable dual-band filter comprises first and second switchable resonators, a coupling structure having two ends respectively connecting the first and the second switchable resonators, an input impedance conversion circuit connecting an input terminal and the first resonator, and an output impedance conversion circuit connecting an output terminal and the second resonator. The coupling structure couples the first resonator to the second resonator, and vice versa. The input/output impedance conversion circuit converts the impedance on the input/output terminal into two distinct impedances that correspond to a first and a second operating frequency. The filter is simple in structure, occupies a smaller circuit area, and is cost-effective in manufacturing. The impedance at both operating passbands can also be matched properly.