FBAR Filter With Lamb Wave Cancellation for RF Isolation
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Solution Overview
Problem
Acoustic wave filters, particularly film bulk acoustic resonator (FBAR) filters, face challenges in achieving effective transmit/receive isolation and attenuation due to the large physical footprint and external implementation of LC circuits used in loop cancellation circuits, which hinder integration and increase power consumption.
Innovation Solution
Integration of Lamb wave loop circuits with FBAR filters, utilizing aluminum nitride (AlN) piezoelectric layers, which generate anti-phase signals to cancel target frequencies, thereby enhancing isolation and attenuation characteristics while reducing physical footprint and manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional LC circuits are used for loop cancellation, then transmit/receive isolation and attenuation can be achieved, but the physical footprint increases and integration becomes difficult
Solution Approach 1:
The patent merges the loop cancellation function with the FBAR filter structure by integrating the cancelation circuit within the filter itself. The shunt resonator and series resonator are combined into a single FBAR device, eliminating the need for separate external LC circuits while maintaining the isolation and attenuation functions.
Solution Approach 2:
The FBAR structure serves multiple functions simultaneously: it acts as both the main filter and the loop cancellation circuit. The piezoelectric layer and electrode structures perform both filtering and signal cancellation operations, reducing the overall component count and physical footprint.
2Reliability
If traditional LC circuits are used for loop cancellation, then attenuation can be achieved, but power consumption increases
Solution Approach 1:
The patent replaces the electrical LC circuit with a piezoelectric-based mechanical resonance system. The FBAR uses piezoelectric material to generate mechanical vibrations at resonant frequencies, which are then converted back to electrical signals for cancellation. This substitution reduces power consumption by utilizing the high Q-factor of piezoelectric resonance rather than continuous electrical oscillation.
3Adaptability or versatility
If external LC circuits are used for loop cancellation, then the function can be implemented, but manufacturing complexity and cost increase
Solution Approach 1:
The loop cancellation circuit is merged with the FBAR filter structure, allowing both functions to be manufactured using the same piezoelectric thin-film deposition processes. The shunt and series resonators share common structural elements, reducing the number of separate manufacturing steps and materials required.
Solution Approach 2:
The patent uses homogeneous piezoelectric material (such as aluminum nitride or zinc oxide) for both the main filter and the loop cancellation circuit. This uniform material selection simplifies the manufacturing process by eliminating the need for different material deposition techniques and reduces assembly 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
The Lamb wave loop circuits improve transmit/receive isolation and attenuation in acoustic wave filters, offering a cost-effective and efficient solution with a smaller physical footprint compared to traditional LC circuits, facilitating integration and reducing power consumption.
Implementation Method 1
an interdigital transducer electrode disposed on the piezoelectric layer, the piezoelectric layer including free edges
Data Source
AI summary
An acoustic wave device includes an acoustic wave filter configured to filter a radio frequency signal and a loop circuit coupled to the acoustic wave filter. The loop circuit is configured to generate an anti-phase signal to a target signal at a particular frequency. The loop circuit includes a Lamb wave resonator having a piezoelectric layer and an interdigital transducer electrode disposed on the piezoelectric layer. The piezoelectric layer includes free edges. An edge of the piezoelectric layer is configured to one of suppress or scatter reflections of acoustic waves generated by the interdigital transducer electrode from the edge of the piezoelectric layer.