Inductively Coupled Acoustic Filter With Wide Passband Control
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Solution Overview
Problem
Acoustic resonators, such as BAW and SAW 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 filter circuitry with inductive coupling and compensation circuits using negatively and positively coupled inductors, along with multiple acoustic resonators and compensation circuits, to create wide passbands and multiple passbands/stopbands, effectively suppressing spurious modes and enhancing filter performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional acoustic resonators are used, then the filter provides basic filtering function, but spurious modes reduce the quality factor and filter performance
Solution Approach 1:
The patent introduces compensation circuits with inductors that have coupling coefficients specifically designed to counteract the harmful spurious modes. The inductors are coupled to acoustic resonators with carefully selected coupling coefficients (e.g., K between 0.3-0.7) to cancel out the unwanted lateral standing waves and improve the overall filter performance.
Solution Approach 2:
The patent modifies the electrical parameters of the filter by introducing inductive elements with specific coupling coefficients. By adjusting the coupling coefficient K and the inductance values, the phase response and quality factor are optimized to eliminate spurious modes while maintaining the desired passband characteristics.
2Volume of moving object
If acoustic resonators operate at high frequencies, then the filter size decreases, but spurious modes become more prominent and reduce quality factor
Solution Approach 1:
The patent introduces inductor-based compensation circuits as intermediary elements between the acoustic resonators. These inductors act as mediators that cancel out the spurious modes generated by lateral standing waves, thereby preserving the high quality factor even at high operating frequencies where the filter size is reduced.
3Reliability
If filter circuitry uses inductive coupling with compensation circuits, then spurious modes are suppressed and passband bandwidth is improved, but device complexity increases
Solution Approach 1:
The patent divides the filter into multiple independent resonator circuits, each with its own compensation circuit. This segmentation allows each resonator-inductor pair to be optimized independently, suppressing spurious modes locally while maintaining overall filter performance. The modular structure makes the complexity manageable through systematic design.
Solution Approach 2:
The compensation circuits with inductors serve multiple functions: they cancel spurious modes, improve the quality factor, and shape the passband response. By using the same basic compensation circuit topology across different resonators with adjusted coupling coefficients, the design achieves multiple performance goals without proportionally increasing complexity.
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 approach significantly improves the filter's passband bandwidth, maintains flat passbands with steep skirts, and provides excellent rejection outside the passbands, addressing the limitations of traditional acoustic resonator filters.
Implementation Method 1
The first inductor and the second inductor are positively coupled with one another... The third inductor and the fourth inductor are negatively coupled with one another
Implementation Method 2
The transducer 16 rests on the reflector 14 and includes a piezoelectric layer 18, which is sandwiched between a top electrode 20 and a bottom electrode 22... applying electrical signals across the top electrode 20 and the bottom electrode 22 excites acoustic waves in the piezoelectric layer 18
Data Source
AI summary
Disclosed in one embodiment is filter circuitry having first and second paths extending between first and second nodes. The first path has a first inductor and a second inductor coupled in series between the first node and the second node, wherein the first inductor and the second inductor are positively coupled with one another, and a first common node is provided between the first inductor and the second inductor. First shunt acoustic resonators are coupled between the first common node and a fixed voltage node. The second path includes a third inductor and a fourth inductor coupled in series between the first node and the second node. The third inductor and the fourth inductor are negatively coupled with one another, and a second common node is provided between the third inductor and the fourth inductor. Second acoustic resonators are coupled between the second common node and a fixed voltage node.