Acoustic Wave Filter Impedance Optimization
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Solution Overview
Problem
Ladder-type filters used in wireless terminals face challenges in improving power durability and linearity without deteriorating insertion loss, particularly in maintaining high impedance to reduce current flow and associated Joule heat generation.
Innovation Solution
The filter design incorporates a ladder circuit with series and parallel acoustic wave resonators, where the characteristic impedance in the passband is set higher than the input and output impedances, using input and output impedance conversion sections to optimize resonator design and electrostatic capacitance, thereby reducing current flow and enhancing power durability and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the impedance of series resonators and parallel resonators is increased to make input/output impedance high, then power durability and linearity are improved, but insertion loss deteriorates
Solution Approach 1:
The patent changes the impedance parameter distribution within the filter circuit. Specifically, it sets the characteristic impedance of the series resonators (Zs) and parallel resonators (Zp) to specific relationships with the input impedance (Zin) and output impedance (Zout). The patent establishes that Zs = k1 × Zin × Zout and Zp = k2 × Zin × Zout, where k1 and k2 are design constants. This parameter optimization allows the resonators to operate at optimal impedance levels that improve power durability while maintaining acceptable insertion loss characteristics.
Solution Approach 2:
The patent applies different impedance characteristics to different parts of the filter circuit. Instead of using uniform impedance throughout, it optimizes the characteristic impedance of series resonators and parallel resonators independently based on their specific functional requirements. The series resonators use a different impedance relationship (k1) compared to parallel resonators (k2), allowing each component to contribute optimally to power durability while minimizing overall insertion loss.
2Reliability
If the characteristic impedance is increased to reduce current flow and Joule heat, then power durability is improved, but the filter performance in passband deteriorates
Solution Approach 1:
The patent optimizes the characteristic impedance parameters of resonators to achieve a balance between power durability and filter performance. By setting Zs = k1 × Zin × Zout and Zp = k2 × Zin × Zout, the patent determines optimal impedance values that reduce current flow and Joule heating in the resonators while maintaining good passband characteristics. The constants k1 and k2 are carefully selected to ensure that the impedance increase improves power durability without excessively degrading filter 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 effectively reduces current values, improving power durability and linearity by increasing characteristic impedance, thereby enhancing the filter's performance in terms of insertion loss and out-of-passband suppression.
Implementation Method 1
series acoustic wave resonators connected in series between the input terminal and the output terminal and one or more parallel acoustic wave resonators connected in parallel
Implementation Method 2
Surface Acoustic Wave (SAW) filters and Bulk Acoustic Wave (BAW) filters
Implementation Method 3
Surface Acoustic Wave (SAW) filters and Bulk Acoustic Wave (BAW) filters
Data Source
AI summary
A filter includes: an input terminal; an output terminal; and a ladder circuit that includes one or more series acoustic wave resonators connected in series between the input terminal and the output terminal and one or more parallel acoustic wave resonators connected in parallel between the input terminal and the output terminal, and in which characteristic impedance of at least one point in a pathway between the input terminal and the output terminal in a passband is greater than at least one of input impedance of the input terminal and output impedance of the output terminal in the passband.