Five-IDT SAW Filter with Asymmetric Electrode Configuration
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Solution Overview
Problem
Existing five-IDT longitudinally-coupled-resonator surface acoustic wave filters struggle with insufficient out-of-band attenuation, particularly in the stop band near the low-frequency side of the pass band, leading to inadequate sharp filter characteristics.
Innovation Solution
The design involves a five-IDT surface acoustic wave filter with a specific configuration where the number of electrode fingers and electrode finger pitches of the IDTs satisfy the relationships N1 < N2, N1 < N3, P1 < P2, and P1 < P3, along with phase differences and balanced/unbalanced signal terminal connections, to enhance attenuation and filter sharpness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of electrode fingers and electrode finger pitch of IDTs satisfy N1 > N2 > N3 and P1 > P2 > P3, then wide-band filter characteristics can be obtained, but out-of-band attenuation cannot be sufficiently increased
Solution Approach 1:
The patent applies parameter changes by inverting the relationships of electrode finger numbers and pitches: N1 < N2, N1 < N3, P1 < P2, and P1 < P3. This reversal of parameters transforms the IDT configuration to achieve both wide bandwidth and high out-of-band attenuation simultaneously, resolving the technical contradiction between bandwidth and attenuation.
2Ease of manufacture
If the number of electrode fingers and electrode finger pitch of IDTs are equalized, then manufacturing simplicity is improved, but sharp filter characteristics cannot be obtained
Solution Approach 1:
The patent employs parameter changes by establishing asymmetric relationships (N1 < N2, N1 < N3, P1 < P2, P1 < P3) among IDT parameters. This deliberate parameter differentiation enables sharp filter characteristics while maintaining reasonable manufacturing complexity through systematic parameter assignment.
3Adaptability or versatility
If the first IDT has the largest number of electrode fingers and largest pitch, then the pass band bandwidth is maximized, but the attenuation in the stop band near the low-frequency side deteriorates
Solution Approach 1:
The patent applies inversion by reversing the conventional parameter assignment: instead of making the first IDT (at the center) have the largest N and P, it makes the first IDT have the smallest N1 and P1. The outer IDTs (second, third, fourth, fifth) have larger parameters. This inverted configuration simultaneously achieves wide pass band and high attenuation near the low-frequency side of the stop band.
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 achieves large attenuation in the stop band near the low-frequency side of the pass band and reduces insertion loss, resulting in sharper filter characteristics and improved out-of-band rejection.
Implementation Method 1
a first IDT disposed on the piezoelectric substrate, second and third IDTs disposed on either side of the first IDT in a direction of propagation of surface waves
Implementation Method 2
in a direction of propagation of surface waves
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
To provide a longitudinally-coupled-resonator surface acoustic wave filter device having a sufficient pass-band width, in which a large attenuation in a stop band near the low-frequency side of a pass band and sharp filter characteristics can be obtained, and low insertion loss in the pass band can be achieved. There is provided a five-IDT longitudinally-coupled-resonator acoustic wave filter device (1) including a first IDT (11), second and third IDTs (12 and 13) disposed on either side of the first IDT (11) in a direction of propagation of surface waves, and fourth and fifth outermost IDTs (14 and 15) in the direction of propagation of surface waves, wherein when the first IDT (11) has the number of electrode fingers N1 and an electrode finger pitch P1, the second and third IDTs (12 and 13) have the number of electrode fingers N2 and an electrode finger pitch P2, and the fourth and fifth IDTs have the number of electrode fingers N3 and an electrode finger pitch P3, a relationship of N1 < N2, N1 < N3, P1 < P2, and P1 < P3 is satisfied.