Acoustic Coupled Resonator Filter for Wider Passbands
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Acoustic resonators, particularly BAW resonators, face challenges in achieving ideal phase curves due to spurious modes caused by lateral standing waves, which reduce the quality factor and filter performance, especially in high-frequency applications.
Innovation Solution
The implementation of a filter circuit with acoustically coupled resonators and compensation circuits, including negatively coupled inductors and shunt resonators, to compensate for capacitance and achieve wider passbands with flat responses and steep skirts, while minimizing the impact of adjacent antenna interference in mobile devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If acoustic resonators are used in high-frequency communication applications, then the filter operates at higher frequencies with smaller size, but spurious modes caused by lateral standing waves reduce the quality factor and filter performance
Solution Approach 1:
A coupling structure is introduced as an intermediary element between two acoustically coupled resonators. This coupling structure mediates the acoustic interaction between resonators, enabling controlled acoustic coupling that enhances filter performance while suppressing spurious modes caused by lateral standing waves within each individual resonator.
Solution Approach 2:
Two acoustically coupled resonators are merged into a single filter system with interconnected electrical and acoustic pathways. The resonators are coupled both electrically through circuit nodes and acoustically through the coupling structure, creating a unified system where the combined resonance characteristics improve the overall quality factor and suppress spurious modes.
2Productivity
If multiple resonators are coupled to achieve wider passbands, then the bandwidth increases, but the device complexity increases
Solution Approach 1:
Multiple resonators are merged into a unified filter structure with shared electrical nodes and acoustic coupling. This merging approach achieves wider passbands through the combined resonance characteristics of multiple resonators while reducing overall complexity compared to traditional cascaded filter designs, as the resonators share common electrical connections and acoustic pathways.
Solution Approach 2:
The filter design transitions from purely electrical coupling to a two-dimensional coupling approach, combining both electrical connections and acoustic coupling between resonators. This additional acoustic dimension enables wider passbands with fewer components, as the acoustic coupling provides an alternative energy transfer pathway that reduces the need for complex electrical interconnections.
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 significantly enhances the quality factor and filter performance by reducing spurious modes, achieving wider passbands and improved rejection of out-of-band signals, and effectively mitigates antenna interference in multi-band communication devices.
Implementation Method 1
applying electrical signals across the top electrode 20 and the bottom electrode 22 excites acoustic waves in the piezoelectric layer 18
Implementation Method 2
the first transducer and the second transducer are vertically aligned such that the first coupling structure vertically acoustically couples the first transducer and the second transducer
Implementation Method 3
Acoustic waves traveling downward are reflected back into the transducer 16 by the reflector 14 or by an air cavity
Data Source
AI summary
A filter circuit includes a first input node and a second input node for receiving an input signal, and a first output node and a second output node for providing an output signal. A first series acoustic resonator is coupled in series between the first input node and the first output node. At least one coupled resonator filter (CRF) includes first and second transducers, which may be acoustically coupled to one another. The first transducer has a first electrode coupled to the first input node, a second electrode coupled to the second input node, and a first piezoelectric layer between the first electrode and the second electrode. A second transducer has a third electrode coupled to the first output node, a fourth electrode coupled to the second output node, and a second piezoelectric layer between the third electrode and the fourth electrode.