Split Ladder Acoustic Resonator Filter for Stable RF Passbands
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Solution Overview
Problem
Conventional RF filters using acoustic wave resonators face challenges in achieving optimal performance across various parameters such as insertion loss, rejection, isolation, power handling, linearity, size, and cost, particularly in achieving stable passbands over a wide temperature range and minimizing spurious modes that affect filter performance.
Innovation Solution
The implementation of a split ladder filter design, where series and shunt resonators are fabricated on separate chips with distinct material stacks, allowing for separate optimization of each, and using bonded-wafer resonators with low thermal expansion and high thermal conductivity to reduce temperature sensitivity and spurious modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional RF filters use a single material stack for all resonators, then manufacturing is simpler, but temperature stability and spurious mode suppression are compromised
Solution Approach 1:
The filter is divided into multiple sections, each with resonators using different material stacks optimized for specific frequency ranges. Series resonators use one material stack while shunt resonators use another, allowing independent optimization of each section for temperature stability and spurious mode suppression.
Solution Approach 2:
Different material stacks are assigned to different parts of the filter based on local requirements. Series resonators in certain sections use material stacks with specific thermal expansion properties, while shunt resonators use different material stacks, enabling localized optimization of temperature compensation and spurious mode control.
2Reliability
If series and shunt resonators use the same material stack, then manufacturing is easier, but individual optimization of each resonator type is prevented
Solution Approach 1:
Series resonators and shunt resonators are segmented into different groups, each using material stacks specifically optimized for their functional requirements. This allows series resonators to be optimized for one set of performance parameters while shunt resonators are optimized for different parameters.
Solution Approach 2:
Different material parameters are selected for series and shunt resonators based on their specific performance requirements. Material stacks are chosen with different thermal expansion coefficients, acoustic impedances, and other parameters to optimize each resonator type's contribution to overall filter performance.
3Stability of the object's composition
If resonators are optimized for wide temperature range, then temperature stability improves, but spurious modes increase
Solution Approach 1:
Different material stacks with different thermal properties are assigned to series and shunt resonators to achieve temperature stability while controlling spurious modes. The local material properties are selected to compensate for temperature effects in each resonator type without generating harmful spurious responses.
Solution Approach 2:
Composite material stacks are used in the resonators, combining multiple layers with different thermal and acoustic properties. These composite structures provide temperature compensation while suppressing spurious modes through controlled acoustic impedance mismatches and resonant frequency separation.
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 spurious modes, and meets specific insertion loss requirements, such as those for LTE Band 2, while also offering cost-effective solutions by optimizing resonator types based on their specific requirements.
Implementation Method 1
Each resonator includes a piezoelectric material
Implementation Method 2
acoustic wave resonators... pass some frequencies and to stop other frequencies
Implementation Method 3
bonded-wafer resonators with low thermal expansion and high thermal conductivity to reduce temperature sensitivity
Data Source
AI summary
Filter devices. A first chip includes a first interdigital transducer (IDT) of a first acoustic resonator formed on a surface of a first piezoelectric wafer having a first thickness, interleaved fingers of the first IDT disposed on a portion of the first piezoelectric wafer spanning a first cavity in a first base. A second chip includes a second IDT of a second acoustic resonator formed on a surface of a second piezoelectric wafer having a second thickness less than the first thickness, interleaved fingers of the second IDT disposed on a portion of the second piezoelectric wafer spanning a second cavity in a second base. A circuit card coupled to the first chip and the second chip includes at least one conductor for making an electrical connection between the first IDT and the second IDT.