Balanced Acoustic Wave Filter Layout for 1:16 Impedance Conversion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing surface acoustic wave filters with balanced-unbalanced conversion functions cannot achieve high-ratio impedance conversion, requiring additional components when the differential amplifier's impedance exceeds 1000Ω, limiting their effectiveness in mobile communication systems.
Innovation Solution
A balanced acoustic wave filter device with a piezoelectric substrate and IDTs configured to provide both balanced-unbalanced conversion and high-ratio impedance conversion, featuring divided IDT portions and sub-divided IDT portions connected in series, along with specific electrode connections and weighting techniques to enhance impedance ratio and out-of-band frequency attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the second IDT is divided into two portions in the surface wave propagating direction, then the impedance ratio is increased to about 1:4, but the impedance conversion function cannot achieve high-ratio conversion when differential amplifier impedance exceeds 1000Ω
Solution Approach 1:
The second IDT is divided into first and second divided IDT portions, and each divided portion is further divided into sub-divided portions (first and second sub-divided IDT portions) in the crossing width direction. This multi-level segmentation increases the impedance ratio from 1:4 to 1:16, enabling high-ratio impedance conversion for differential amplifiers with impedance exceeding 1000Ω.
Solution Approach 2:
The division of IDT portions extends from one dimension (surface wave propagating direction) to another dimension (crossing width direction). By dividing in both directions, the patent achieves higher impedance conversion ratio without simply extending the structure in one direction, optimizing space utilization while achieving 1:16 impedance ratio.
2Manufacturing precision
If additional components are added for impedance conversion, then high-ratio impedance conversion can be achieved, but the device complexity increases
Solution Approach 1:
The acoustic wave filter device integrates multiple functions into a single structure: it provides both balanced-unbalanced conversion and high-ratio impedance conversion (1:16) simultaneously. The divided and sub-divided IDT portions enable the filter to serve as both a signal filter and an impedance transformer, eliminating the need for separate balun and impedance matching components.
Solution Approach 2:
The patent combines the functions of the balun (balanced-unbalanced conversion) and impedance matching network into the acoustic wave filter structure itself. By integrating these functions, the overall device complexity is reduced while achieving the required 1:16 impedance conversion ratio for high-impedance differential amplifiers.
3Manufacturing precision
If the IDT portions are divided and connected in series, then the impedance is increased, but the out-of-band frequency attenuation may be degraded
Solution Approach 1:
The patent applies different configurations to different parts of the IDT structure. The first and third IDTs are configured with specific electrode finger arrangements and grounding schemes, while the second IDT and its divided portions have optimized configurations. This local optimization ensures that each region contributes to both impedance conversion and out-of-band attenuation performance.
Solution Approach 2:
The patent converts the potential harmful effect of direct arrival waves (which cause poor out-of-band attenuation) into a beneficial structure by strategically grounding specific electrode fingers and configuring the divided IDT portions. This transforms the direct wave path into a controlled impedance transformation mechanism that simultaneously achieves 1:16 impedance ratio and maintains good out-of-band attenuation.
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
The device achieves a high-ratio impedance conversion of 1:16, eliminating the need for additional components and improving out-of-band frequency attenuation, while maintaining superior filter characteristics by adjusting excitation strengths across different acoustic tracks.
Implementation Method 1
a piezoelectric substrate and first to third IDTs disposed on the piezoelectric substrate in a surface wave propagating direction
Implementation Method 2
first to third IDTs disposed on the piezoelectric substrate in a surface wave propagating direction
Data Source
AI summary
A surface acoustic wave filter device includes an unbalanced terminal, first and second balanced terminals, and first, second and third IDTs. One end of the first IDT and one end of the third IDT are connected to the unbalanced terminal. The second IDT includes first and second divided IDT portions obtained by dividing the IDT in the surface wave propagating direction. The first and second divided IDT portions include sub-divided IDT portions and sub-divided IDT portions obtained by dividing the first and second divided IDT portions and in the crossing width direction. The first and second divided IDT portions are electrically connected in series. The first and second sub-divided IDT portions are electrically connected in series. The first and second sub-divided IDT portions are electrically connected in series. The second sub-divided IDT portion is connected to the first balanced terminal and the second sub-divided IDT portion is connected to the second balanced terminal.