Acoustically Coupled SAW Filter With Phase Rotation for Wider Attenuation
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Solution Overview
Problem
Conventional surface acoustic wave (SAW) filters with acoustic coupling structures face challenges in achieving a wide and large attenuation range outside the pass band without degrading the characteristics within the pass band, as they tend to abruptly reduce attenuation further away from the pass band, leading to increased insertion loss.
Innovation Solution
Incorporating a phase rotating element connected in parallel with at least one of the acoustically coupled interdigital transducers, which can form a new attenuation pole, thereby expanding the attenuation range, and adjusting the electrode finger pitches and element values to optimize the attenuation and insertion loss characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the attenuation characteristic out of the pass band is improved by conventional SAW filter designs, then the insertion loss increases in the pass band
Solution Approach 1:
The filter is divided into multiple resonators (first resonator, second resonator, third resonator) with different configurations. The first and second resonators provide attenuation out of the pass band, while the third resonator is optimized to maintain low insertion loss within the pass band, allowing independent optimization of different frequency regions
Solution Approach 2:
Different resonators are designed with different local characteristics: the first resonator has a reflector configuration optimized for attenuation, the second resonator has different electrode finger pitch for complementary attenuation, and the third resonator has optimized connection structure for minimal loss in the pass band, allowing each part to serve its specific function
2Object-affected harmful factors
If the attenuation range out of the pass band is extended, then the insertion loss in the pass band increases
Solution Approach 1:
The filter is divided into multiple resonators (first resonator, second resonator, third resonator) with different configurations. The first and second resonators provide attenuation out of the pass band, while the third resonator is optimized to maintain low insertion loss within the pass band, allowing independent optimization of different frequency regions
Solution Approach 2:
Different resonators are designed with different local characteristics: the first resonator has a reflector configuration optimized for attenuation, the second resonator has different electrode finger pitch for complementary attenuation, and the third resonator has optimized connection structure for minimal loss in the pass band, allowing each part to serve its specific function
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 enhances the attenuation characteristic outside the pass band while maintaining low insertion loss within the pass band, resulting in improved filter performance with a wider and flatter attenuation range.
Implementation Method 1
Surface acoustic wave apparatuses which utilize a surface acoustic wave (SAW) generated by the piezo-electric effect
Data Source
AI summary
A surface acoustic wave apparatus includes an input terminal, an output terminal, a plurality of acoustically coupled interdigital transducers (IDT), and a phase rotating element (line or inductor) connected in parallel with one or more IDT's. The acoustically coupled IDT's are connected in series between the input and output terminals. Alternatively, the acoustically coupled IDT's may include a series IDT to which the phase rotating element is connected and which is connected in series between the input and output terminals, and a branch IDT acoustically coupled to the series IDT, and disposed on a transmission path which branches from a transmission path between the input and output terminals to a reference potential. Among the plurality of IDT's, λa≧λb is established, where λa represents an electrode finger pitch of the IDT to which the phase rotating element is connected, and λb represents an electrode finger pitch of the IDT to which no phase rotating element is connected.