Split Ladder Acoustic Filter Using Separate Series and Shunt Chips
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Solution Overview
Problem
Current RF filters using acoustic wave resonators face challenges in achieving optimal performance across various parameters such as insertion loss, rejection, isolation, power handling, and temperature stability due to the need for a single material stack that meets the distinct requirements of series and shunt resonators, leading to suboptimal filter performance in communications devices.
Innovation Solution
The implementation of a split ladder filter design, where series and shunt resonators are fabricated on separate chips with different material stacks, allowing for separate optimization of each, thereby improving temperature stability and reducing spurious modes that affect filter performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single material stack is used for both series and shunt resonators, then device complexity is reduced, but filter performance deteriorates due to inability to meet distinct requirements of series and shunt resonators
Solution Approach 1:
The filter is divided into two separate modules: a first module containing series resonators with a first material stack optimized for series resonator requirements, and a second module containing shunt resonators with a second material stack optimized for shunt resonator requirements. This segmentation allows each material stack to be independently optimized for its specific function, resolving the contradiction between device complexity and filter performance.
2Reliability
If series and shunt resonators are optimized separately with different material stacks, then filter performance improves, but device complexity increases due to multiple material stacks
Solution Approach 1:
The first module containing series resonators and the second module containing shunt resonators are combined into a single integrated filter device. This merging allows the filter to achieve optimal performance through separate material stack optimization while maintaining a unified device structure, thus improving filter performance without excessive increase in overall device complexity.
3Stability of the object's composition
If bonded-wafer series resonators are used, then temperature stability improves, but manufacturing complexity increases
Solution Approach 1:
The bonded-wafer construction is applied specifically to the series resonators in the first module where temperature stability is critical for maintaining resonance characteristics. The shunt resonators in the second module can use alternative construction methods. This localized application of bonded-wafer technology provides temperature stability where needed without unnecessarily complicating the entire manufacturing process.
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 enhances the stability of the filter passband over a wide temperature range, reduces power dissipation, and meets specific insertion loss requirements, such as those for LTE Band 2, while maintaining lower costs by using bonded-wafer series resonators and non-bonded SAW shunt resonators.
Implementation Method 1
The first resonator includes a first piezoelectric material and the second resonator includes a second piezoelectric material
Implementation Method 2
acoustic wave resonators face challenges in achieving optimal performance
Data Source
AI summary
Filter devices. A first chip includes a first base, a first piezoelectric membrane having a first thickness, and a first acoustic Bragg reflector sandwiched between the first piezoelectric membrane and the first base. A first interdigital transducer (IDT) of a first solidly-mounted membrane resonator is formed on a surface of the first piezoelectric membrane. A second chip includes a second base, a second piezoelectric membrane having a second thickness less than the first thickness, and a second acoustic Bragg reflector sandwiched between the second piezoelectric membrane and the second base. A second IDT of a second solidly-mounted membrane resonator is formed on a surface of the second piezoelectric membrane. A circuit card is coupled to the first chip and the second chip, the circuit card including at least one conductor for making an electrical connection between the first IDT and the second IDT.