Quadplexer Filter Layout for Pass-Band Ripple Suppression
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Solution Overview
Problem
In multiplexers, such as quadplexers, the characteristics of one filter can degrade the performance of another due to stop-band ripple interference, particularly when the frequency of the ripple falls within the pass band of another filter, leading to increased ripple in the pass band.
Innovation Solution
A multiplexer configuration with a first filter having series and parallel resonators, including a slanted IDT electrode with variant fingers, where the ratio of variant fingers is lower near the common terminal, reduces pass-band ripple without degrading the first filter's characteristics, by using a substrate with a piezoelectric layer and high/low-acoustic-velocity supporting structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If stop-band ripple of one filter is reduced, then pass-band ripple of another filter is reduced, but insertion loss of the first filter increases
Solution Approach 1:
The patent applies local quality by making the IDT electrode fingers non-uniform in width along the propagation direction. Specifically, the finger width varies in different regions (wider at input, narrower at output) to locally adjust the impedance and acoustic wave distribution, thereby reducing stop-band ripple without significantly increasing overall insertion loss.
Solution Approach 2:
The patent changes the geometric parameters of the IDT electrode fingers, specifically varying the width of the fingers along the elastic wave propagation direction. This parameter change modifies the impedance profile and acoustic coupling, which reduces the stop-band ripple that would otherwise appear as pass-band ripple in adjacent filters.
2Ease of manufacture
If uniform IDT electrode fingers are used, then manufacturing is simplified, but pass-band ripple increases due to stop-band interference
Solution Approach 1:
Instead of uniform fingers, the patent implements local quality variations by making the IDT electrode finger widths different at different positions. This local variation complicates manufacturing slightly but effectively suppresses the stop-band ripple that causes pass-band interference.
Solution Approach 2:
The patent deliberately changes the geometric parameters (width) of the IDT electrode fingers from uniform to non-uniform distribution. This parameter modification trades some manufacturing complexity for significant reduction in pass-band ripple.
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 or prevents pass-band ripple in the second filter while maintaining low-loss characteristics in the first filter, even with varying electrode parameters, enhancing filter performance in multiband communication devices.
Implementation Method 1
an IDT electrode and a reflector that are provided on a substrate including a piezoelectric layer
Implementation Method 2
an IDT (interdigital transducer) electrode and a reflector that are provided on a substrate including a piezoelectric layer
Data Source
AI summary
A quadplexer includes a first filter and a second filter having a pass band frequency that is higher than a pass band frequency of the first filter. The first filter includes series resonators disposed on a first path and parallel resonators disposed on a path that connects the first path and a ground to each other. A direction that connects ends of a plurality of electrode fingers defining each resonator crosses an elastic wave propagation direction at a predetermined angle. The series resonator nearest to a common terminal does not include first electrode fingers, and the other series resonators include the first electrode fingers.