SAW Filter Resonator Layout for Ripple and Interference Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Bandpass filters using surface acoustic wave (SAW) elements in communication devices experience ripples in bandpass characteristics due to unwanted waves, particularly Rayleigh waves, which affect attenuation characteristics and can interfere with other bandpass filters connected to a common terminal.
Innovation Solution
The use of SAW filters with multiple parallel-connected divided resonators, each with interdigital transducers (IDTs) having different pitches, reduces ripples caused by unwanted waves by distributing the resonance frequencies and minimizing the impact on passband and stopband characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple SAW resonators are connected to form a bandpass filter, then the desired pass band characteristics are achieved, but ripples occur in the stopband due to unwanted waves such as Rayleigh waves
Solution Approach 1:
Each SAW resonator is divided into multiple divided resonators (first, second, third, and fourth divided resonators) with different IDT pitch values. This segmentation distributes the resonance frequencies of unwanted waves across different frequency points, preventing the formation of large ripples in the stopband while maintaining the desired passband characteristics.
2Adaptability or versatility
If multiple bandpass filters with different pass bands are connected to a single common terminal, then multiple frequency bands are supported, but ripples from one filter adversely influence the pass band of another filter
Solution Approach 1:
Each SAW resonator is designed with divided resonators having different local characteristics (different IDT pitch values). This creates local quality differences that cause unwanted waves from different resonators to occur at different frequency points, reducing mutual interference between filters connected to the same common terminal and improving isolation between frequency bands.
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 effectively reduces the insertion loss caused by ripples, maintaining desired filter characteristics and minimizing interference between bandpass filters with different passbands, while allowing for design flexibility without significant changes to existing filter configurations.
Implementation Method 1
a filter using surface acoustic wave (SAW) elements is utilized
Implementation Method 2
The substrate is made of a piezoelectric material
Implementation Method 3
resonance may be produced due to unwanted waves, such as Rayleigh waves, at a frequency lower than the fundamental resonant frequency of the main waves
Data Source
AI summary
A filter device includes a first filter connected between a common terminal and a first individual terminal, and a second filter connected between the common terminal and a second individual terminal. A pass band of the second filter is in a frequency range lower than a pass band of the first filter. The first filter includes SAW resonators, at least one of which includes divided resonators connected in parallel with each other. Each of the divided resonators includes an IDT. A pitch of the IDT of one of the divided resonators is different from that of another of the divided resonators.