Acoustically Coupled Resonator Tuning for Compact RF Filters
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Solution Overview
Problem
Conventional surface acoustic wave (SAW) and bulk acoustic wave (BAW) filters in communication devices require a large number of discrete components due to fixed resonance frequencies, leading to increased circuit complexity, radio frequency losses, and limited space in mobile devices, necessitating the development of tunable filters with improved tuning range and selectivity.
Innovation Solution
The use of a resonator element comprising a first resonator acoustically coupled to a second resonator, with a tuning circuit including a variable capacitor and inductor, allows for frequency tuning by shifting resonances, enabling the creation of tunable RF filters with reduced component count and enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fixed-frequency SAW or BAW filters are used for each frequency band, then high selectivity and bandwidth are achieved, but the number of filters and discrete components increases significantly
Solution Approach 1:
A single BAW filter structure is designed to perform multiple functions by supporting different resonance modes (fundamental and overtone modes) that can be selectively excited. The filter can operate at different frequency bands by controlling which resonance mode is activated, eliminating the need for separate physical filters for each band.
Solution Approach 2:
The filter incorporates variable capacitance elements that allow dynamic tuning of the resonance frequency. By changing the capacitance values, the filter can be tuned to different frequency bands and modes of operation, transforming a static filter into a dynamically adjustable one.
2Reliability
If multiple discrete filters are used for different frequency bands, then each filter can be optimized for its specific band, but the space required in mobile devices increases
Solution Approach 1:
Multiple filter functions for different frequency bands are merged into a single BAW filter structure. The filter uses different resonance modes (fundamental mode for lower frequencies, overtone modes for higher frequencies) within the same physical structure, combining multiple functions into one compact device.
Solution Approach 2:
The filter structure utilizes nested resonance modes where higher frequency overtone modes are embedded within the same physical structure as the lower frequency fundamental mode. This nesting allows multiple frequency bands to be handled by a single compact filter.
3Adaptability or versatility
If conventional tuning techniques are applied to SAW or BAW filters, then some frequency adjustment is possible, but tuning range and selectivity are limited and losses increase
Solution Approach 1:
The filter employs variable capacitance elements that allow continuous adjustment of resonance frequency by changing electrical parameters (capacitance values). This electrical tuning method provides wide frequency range adjustment without the mechanical wear and high losses associated with conventional mechanical tuning techniques.
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 solution enables the reduction of the number of filters required in communication devices, improving tuning range and selectivity while minimizing radio frequency losses and circuit complexity, thus optimizing space usage in mobile devices.
Implementation Method 1
a second resonator having a third terminal and a fourth terminal, where the second resonator is acoustically coupled to the first resonator
Implementation Method 2
allows for frequency tuning by shifting resonances
Implementation Method 3
a tuning circuit coupled to the third and fourth terminals... the tuning circuit includes at least one of a variable capacitor and an inductor
Implementation Method 4
the tuning circuit includes at least one of a variable capacitor and an inductor
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A resonator element for use in a filter is provided. The resonator element includes a first resonator (62) acoustically coupled to a second (65) or third resonator or both. The first resonator has terminals (3,4) for incorporation in a filter structure. A tuning circuit is coupled to the second or third resonator or both to enable tuning of the resonator element. The tuning circuit includes a variable capacitor (67) and an inductor (66).