Tunable RF Filter Topology With Impedance Inverters
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Solution Overview
Problem
Existing tunable RF filters alter important parameters such as insertion loss and impedance during tuning, making them complex and unstable for use in portable communication devices.
Innovation Solution
The use of series-interconnected basic elements with impedance converters, specifically impedance or admittance inverters, allows for tuning without significant changes in insertion loss and impedance, stabilizing the filter behavior by converting series resonators to parallel resonators and vice versa.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If tunable RF filters are used to replace multiple conventional filters, then the number of filters is reduced and design flexibility is improved, but insertion loss and impedance parameters change during tuning
Solution Approach 1:
Impedance inverters are introduced as intermediary elements between the series resonators and the signal path. These inverters transform the impedance characteristics of the series resonators, enabling stable impedance parameters during tuning while maintaining the desired frequency selectivity and tunability of the filter.
Solution Approach 2:
The patent employs parameter changes by utilizing impedance inverters with specific impedance values that compensate for the variations in resonator parameters during tuning. By carefully selecting the inverter parameters, the overall filter maintains stable insertion loss and impedance characteristics despite changes in resonator frequency.
2Manufacturing precision
If multiple conventional filters are used for different frequency bands, then frequency selectivity is achieved, but the front-end module size and production complexity increase
Solution Approach 1:
The patent creates a universal filter design that can operate across multiple frequency bands by using tunable series resonators combined with impedance inverters. This single filter structure replaces what would traditionally require multiple separate filters, reducing module complexity while maintaining the ability to achieve precise frequency selectivity for different transmission systems.
Solution Approach 2:
The filter incorporates dynamically adjustable parameters through tunable resonators that can be adjusted to different frequency points. This dynamic capability allows one filter to perform the function of multiple fixed-frequency filters, simplifying the overall module design while preserving frequency selectivity requirements.
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
This configuration enables more stable tuning of RF filters, maintaining consistent impedance and insertion loss, and allows for the creation of filters with steep edges suitable for duplexer applications, reducing the need for multiple filters and simplifying design.
Implementation Method 1
The impedance converters are impedance inverters and/or admittance inverters. A series interconnection of two impedance inverters with a series resonator therebetween looks like a parallel resonator to the circuit environment thereof. A series interconnection of two admittance inverters with a parallel resonator therebetween looks like a series resonator to the circuit environment thereof.
Implementation Method 2
The filter furthermore comprises impedance converters interconnected in series between the basic elements. The resonators of the basic elements are either only series resonators or only parallel resonators.
Data Source
AI summary
An RF filter is disclosed. In an embodiment, the RF filter includes series-interconnected basic elements, each basic element having an electroacoustic resonator and impedance converters interconnected in series between the basic elements, wherein the impedance converters are impedance inverters and/or admittance inverters, and wherein the resonators of the basic elements are either only series resonators or only parallel resonators.