Parallel SAW Filter Weighting for Near-Passband Attenuation
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Solution Overview
Problem
Conventional surface acoustic wave (SAW) filter devices face challenges in achieving sufficient attenuation in the attenuation band near the passband, particularly in mobile communication apparatuses, where existing configurations either fail to reduce insertion loss effectively or do not provide adequate balance between signal terminals.
Innovation Solution
The proposed acoustic wave filter device employs a configuration with multiple longitudinally coupled resonator SAW filters connected in parallel, where at least one filter is withdrawal-weighted differently from the others, allowing for asymmetrical weighting with respect to the central IDT, and all IDTs may be withdrawal-weighted, to adjust attenuation characteristics in the attenuation band without affecting the passband.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If multiple longitudinally coupled resonator SAW filters are connected in parallel to reduce insertion loss, then the resistance of electrode fingers is reduced to a quarter, but the attenuation in the attenuation band near the passband becomes insufficient
Solution Approach 1:
The patent applies different withdrawal weighting patterns to different IDTs within the parallel-connected filters. Specifically, some IDTs use a first withdrawal weighting pattern while others use a second withdrawal weighting pattern, creating local variations in the attenuation characteristics. This allows each IDT to contribute differently to the overall frequency response, enabling sufficient attenuation in the attenuation band near the passband while maintaining low insertion loss through the parallel configuration.
2Ease of operation
If withdrawal weighting is applied to improve balance between signal terminals, then the degree of balance is improved, but the attenuation in the attenuation band near the passband remains insufficient
Solution Approach 1:
The patent employs asymmetric withdrawal weighting patterns where different IDTs have different weighting characteristics. The first withdrawal weighting and second withdrawal weighting are deliberately made asymmetric to each other, creating different attenuation responses. This asymmetry allows the parallel combination to achieve both balance improvement (through the withdrawal weighting effect) and sufficient attenuation (through the differential patterns that create notches in the attenuation 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 enables increased attenuation in the attenuation band near the passband, improving the filter characteristic by allowing for precise adjustment of attenuation-frequency characteristics, thereby enhancing the performance of bandpass filters in both receiver and transmitter sides of mobile communication systems.
Implementation Method 1
various types of surface acoustic wave (SAW) filter devices have been used as bandpass filters
Implementation Method 2
an acoustic wave filter device including a piezoelectric substrate; and a plurality of longitudinally coupled resonator acoustic wave filters provided on the piezoelectric substrate
Implementation Method 3
longitudinally coupled resonator acoustic wave filters... Each of the longitudinally coupled resonator acoustic wave filters includes an input terminal, an output terminal, an IDT connected to the input terminal, and an IDT connected to the output terminal
Data Source
Figure 1~2(c)
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Figure 5~6
AI summary
The present invention provides an acoustic wave filter device capable of adjusting and increasing an attenuation in an attenuation band near a passband with hardly affecting a filter characteristic in the passband. In an acoustic wave filter device 1, first and second longitudinally coupled resonator SAW filters 7 and 8 are provided on a piezoelectric substrate 1. The first and second longitudinally coupled resonator SAW filters 7 and 8 connect in parallel to each other. The first and second longitudinally coupled resonator SAW filters 7 and 8 are withdrawal-weighted. The withdrawal weighting in at least the longitudinally coupled resonator SAW filter 7 is different from the withdrawal weighting in the other longitudinally coupled resonator SAW filter 8.