Tunable Duplexer HF Filters With Impedance Inversion Stability
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Solution Overview
Problem
Tunable HF filters face challenges in adjusting center frequency without altering important parameters like insertion loss, input impedance, and output impedance, limiting design flexibility in duplexer applications.
Innovation Solution
A duplexer design incorporating series-connected basic elements with electro-acoustic resonators and impedance converters, where at least one resonator is tunable, allowing for impedance inversion to maintain stability during tuning, enabling filters to operate with series or parallel resonators without requiring both types, thus simplifying tuning and design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If tunable RF filters are used to reduce the number of filters, then device complexity is reduced, but insertion loss and impedance parameters change during tuning
Solution Approach 1:
The patent inverts the traditional ladder filter structure by placing series resonators in parallel branches and using impedance inverters to transform them into series-equivalent behavior. This inversion allows the filter to maintain stable insertion loss and impedance characteristics while enabling frequency tuning through varactor diodes, resolving the contradiction between filter reduction and parameter stability.
Solution Approach 2:
The patent changes the electrical parameters of the resonators by introducing impedance inverters with specific inversion factors (K values) that transform the resonant characteristics. By adjusting the inversion factors and resonator parameters, the filter achieves frequency tuning while maintaining stable insertion loss and impedance, addressing the reliability concern during tuning operations.
2Ease of manufacture
If traditional ladder filter structure is used, then filter design is straightforward, but device area and production complexity increase
Solution Approach 1:
The patent segments the traditional ladder filter into basic elements consisting of series resonators coupled through impedance inverters. This segmentation allows for compact arrangement of components and reduces the overall front-end module area while maintaining filter design simplicity through modular basic elements that can be systematically connected.
Solution Approach 2:
The patent creates universal basic elements that can be configured for different frequency bands and filter types (low-pass, high-pass, band-pass, band-stop) by adjusting the impedance inverter parameters and resonator characteristics. This multi-functionality reduces the need for multiple dedicated filters, thereby reducing device area while keeping design procedures standardized and simple.
3Reliability
If both series and parallel resonators are used in ladder structure, then filter performance is optimized, but tuning stability deteriorates
Solution Approach 1:
The patent inverts the traditional approach by using only series resonators in parallel branches and employing impedance inverters to achieve the series-equivalent behavior traditionally provided by series resonators. This uniform resonator type configuration significantly improves impedance stability during tuning while the impedance inverters maintain the necessary filter performance characteristics.
Solution Approach 2:
The patent introduces impedance inverters as intermediary elements that mediate between the parallel-connected series resonators and the signal path. These inverters transform the parallel resonator configuration into series-equivalent behavior, maintaining filter performance while enabling stable tuning operations without the impedance variability introduced by mixed resonator types.
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 approach allows for easier tuning of HF filters, maintaining stability in insertion loss and impedance parameters, and provides flexibility in designing bandpass or band-stop filters with steep edges, suitable for duplexer applications.
Implementation Method 1
The RF filter comprises series-connected basic elements, each with an electroacoustic resonator
Implementation Method 2
The electroacoustic properties of resonators operating with acoustic waves are modified by tunable impedance elements
Data Source
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AI summary
The invention relates to a high-frequency filter, in which the characteristic filter values have a reduced dependence on tuning. A filter comprises base members which are connected in series, each base member having an electroacoustic resonator and impedance converters which are connected in series between the base members.