Acoustic Filter Topology for Low-Reflection Stopband Matching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Traditional acoustic filters often exhibit high reflection coefficients in their stopbands, requiring quarter wavelength lines or LC equivalent circuits, which are undesirable due to size and loss issues, and typically need inductors to resonate out static capacitance, degrading the steepness of passband transition regions.
Innovation Solution
The development of reflectionless acoustic filters that do not require quarter wavelength lines or LC equivalent circuits and omit inductors, utilizing bulk acoustic wave (BAW) or surface acoustic wave (SAW) resonators with associated matching components to achieve reduced reflections and improved return loss, allowing for smaller size and steeper passband transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If quarter wavelength lines or LC equivalent circuits are used to reduce reflection coefficients, then return loss is improved, but device size increases and energy loss increases
Solution Approach 1:
The patent extracts and eliminates the quarter wavelength lines and LC equivalent circuits from the filter design, achieving reduced reflections and improved return loss through an alternative acoustic resonator configuration that does not require these traditional impedance matching components
Solution Approach 2:
The patent replaces the electrical impedance matching mechanisms (quarter wavelength lines and LC circuits) with an acoustic field-based solution using acoustic resonators, substituting a mechanical/acoustic system for the electrical system to achieve the same reflection reduction goal
2Reliability
If inductors are added to resonate out static capacitance, then reflection coefficients are reduced, but passband transition steepness degrades
Solution Approach 1:
The patent removes inductors from the filter design, achieving reduced reflection coefficients through the acoustic resonator configuration alone, thereby maintaining sharp passband transitions without the need for inductive components that would degrade transition steepness
3Ease of manufacture
If traditional acoustic filter design is used, then manufacturing is simpler, but reflection coefficients are high and return loss is poor
Solution Approach 1:
The patent changes the fundamental operating parameters by using acoustic resonators configured to operate in specific modes that inherently provide impedance matching and reflection reduction, eliminating the need for additional matching components while improving return loss
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
These filters achieve significantly reduced reflections and improved return loss across a frequency range, maintaining the size and steepness of passband transitions while minimizing insertion loss and Q values, with the option to tune return loss for specific frequency ranges.
Implementation Method 1
utilizing bulk acoustic wave (BAW) or surface acoustic wave (SAW) resonators
Implementation Method 2
utilizing bulk acoustic wave (BAW) or surface acoustic wave (SAW) resonators
Implementation Method 3
utilizing bulk acoustic wave (BAW) or surface acoustic wave (SAW) resonators with associated matching components
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
Embodiments of an acoustic filter are disclosed. In some embodiments, a bandpass filter is included in a passband signal path, the passband signal path is connected between a first terminal and a second terminal. A first bandstop filter is located in a first stopband signal path, the first stopband signal path connected at the first terminal. Additionally, a second bandstop filter is located in a second stopband signal path, the second stopband signal path is connected at the second terminal.