BAW Filter Topology With Parallel Resonators for Steep Skirts
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Solution Overview
Problem
Bulk acoustic wave (BAW) filters face challenges in achieving low-loss and high-skirt characteristics, which are difficult to implement compared to metal cavity filters and wave guides.
Innovation Solution
The acoustic wave filter design includes a series of first series resonators, shunt resonators, second series resonators connected in parallel, and an inductor connected between a shunt resonator and ground, with specific resonant frequency relationships to enhance inband flatness and skirt characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If BAW filter structure is used, then small size and lightweight are achieved, but RF performance (low-loss and high-skirt characteristics) deteriorates
Solution Approach 1:
The filter is divided into multiple resonator units (series resonators and shunt resonators) with specific configurations. Each resonator is designed with particular resonant frequency relationships to collectively achieve low-loss and high-skirt characteristics while maintaining compact size
Solution Approach 2:
The patent optimizes specific parameters including resonant frequencies of different resonators, coupling coefficients, and impedance values to achieve the desired RF performance. The resonant frequency relationships (e.g., fs2 < fs1, fs3 = fs1) are carefully controlled to improve loss and skirt characteristics
2Speed
If bandwidth is increased, then pass bandwidth improves, but loss increases and skirt characteristics worsen
Solution Approach 1:
The filter employs a dynamic resonator configuration where second series resonators are connected in parallel with first series resonators at specific nodes. This creates adaptive impedance transformation that maintains low loss across wide bandwidth while preserving sharp skirt characteristics
Solution Approach 2:
Shunt resonators are introduced as intermediary elements between series resonators and ground. These shunt resonators with specific resonant frequencies act as mediators to control signal distribution, reducing loss and improving skirt characteristics across the bandwidth
3Reliability
If inband flatness is improved, then signal quality improves, but device complexity increases
Solution Approach 1:
Each resonator unit is designed to serve multiple functions: series resonators provide both impedance matching and frequency selection, while shunt resonators simultaneously control flatness and rejection. This multi-functionality achieves good inband flatness without proportionally increasing complexity
Solution Approach 2:
The patent applies different resonator configurations at different locations within the filter. Specific nodes have second series resonators connected in parallel, while other nodes have shunt resonators to ground. This localized optimization achieves uniform inband flatness across the entire passband
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 design achieves improved inband flatness and steeper skirt characteristics, enhancing the performance of RF signals by compensating frequency band flatness and forming additional poles for better signal transmission.
Implementation Method 1
acoustic wave filter includes: a plurality of first series resonators connected in series between a first port and a second port; a plurality of shunt resonators, each shunt resonators being connected between a different node disposed between the first port and the second port and the ground
Implementation Method 2
A resonant frequency of the shunt resonator connected to the inductor is the same as a resonant frequency of at least one of the plurality of first series resonators
Data Source
AI summary
An acoustic wave filter includes: a plurality of first series resonators connected in series between a first port and a second port; a plurality of shunt resonators, each shunt resonators being connected between a different node disposed between the first port and the second port and the ground; at least one second series resonator connected in parallel to at least one of the first series resonators; and an inductor connected between one of the shunt resonators and the ground. A resonant frequency of the shunt resonator connected to the inductor is the same as a resonant frequency of at least one of the plurality of first series resonators.