Asymmetric Acoustic Multiplexer Layout for Lower-Band Insertion Loss
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Solution Overview
Problem
In multiplexers with longitudinally coupled acoustic wave resonators, the insertion loss in the pass band of one filter can degrade due to the first order resonant mode generated in the resonator, especially when another filter has a lower frequency pass band.
Innovation Solution
The multiplexer design includes a first filter with an asymmetrically shaped interdigital transducer electrode group, where the aggregate average of electrode finger pitches and the sum of pairs of electrode fingers on one side are smaller than on the other side, reducing the impact of the first order resonant mode on a second filter with a lower frequency pass band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an asymmetric interdigital transducer electrode group is configured to generate a first order resonant mode, then the steepness in the lower frequency range below the pass band is improved, but the insertion loss in the pass band of another filter with lower frequency degrades
Solution Approach 1:
The patent applies asymmetry by configuring the interdigital transducer electrode group with different numbers of electrode fingers on each side of the center line, creating an asymmetric structure that generates a first order resonant mode. This asymmetric configuration is specifically designed to improve the steepness in the lower frequency range while controlling the impact on adjacent pass bands through careful design of the asymmetry parameters.
Solution Approach 2:
The patent changes physical parameters of the interdigital transducer electrode group, specifically the number of electrode fingers on each side and the electrode finger pitch, to control the resonant mode characteristics. By adjusting these parameters, the patent optimizes the steepness in the lower frequency range while minimizing degradation of insertion loss in adjacent pass bands.
2Power
If the number of electrode fingers on one side of the interdigital transducer electrode group is increased, then the first order resonant mode is enhanced, but the insertion loss degradation in the lower frequency pass band worsens
Solution Approach 1:
The patent applies local quality by creating different configurations of electrode fingers on opposite sides of the center line. Each side has a specific number of electrode fingers optimized for its local function: one side generates the resonant mode while the other side is configured to minimize harmful effects on adjacent pass bands. This localized optimization resolves the contradiction between enhancing the resonant mode and maintaining insertion loss performance.
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 reduces or prevents degradation of insertion loss in the pass band of the second filter by moving the first order resonant mode to a higher frequency range, minimizing ripple and impedance mismatch, thereby improving signal transmission.
Implementation Method 1
a longitudinally coupled acoustic wave resonator including an interdigital transducer electrode group including a plurality of interdigital transducer electrodes along an acoustic wave propagation direction
Implementation Method 2
a first order resonant mode is generated by configuring the longitudinally coupled acoustic wave resonator in such a manner as to have an asymmetric structure
Data Source
AI summary
A multiplexer includes a first filter and a second filter with a lower pass band than that of the first filter. A longitudinally coupled acoustic wave resonator of the first filter includes an interdigital transducer electrode group of interdigital transducer electrodes having an asymmetric shape with respect to a center line that passes through a center of the interdigital transducer electrode group and is perpendicular or substantially perpendicular to an acoustic wave propagation direction. The interdigital transducer electrodes connected to a first path on a common terminal side when seen from the longitudinally coupled acoustic wave resonator have a smaller aggregate average of electrode finger pitches of the interdigital transducer electrodes and a smaller sum of numbers of pairs of electrode fingers of the interdigital transducer electrodes, compared with the interdigital transducer electrodes connected to the first path on a first terminal side.