Coupled Lamb Wave Resonator Filter for Narrow IF Passbands
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Solution Overview
Problem
Coupled resonator filters face challenges in achieving narrow passbands for intermediate frequencies and channel filtering due to high input/output impedances and large dimensions, which complicates manufacturing and increases costs and size, especially when filtering at intermediate frequencies.
Innovation Solution
A coupled Lamb wave resonator filter is designed using at least two Lamb wave resonators with specific electrode configurations and acoustic coupling, allowing for integration onto an integrated circuit, with the ability to modulate resonance using control voltage and incorporating a Bragg mirror or periodic lattice to reduce parasitic resonances and improve manufacturing reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional coupled resonator filters are used for intermediate frequency filtering, then the filter can operate at the required frequency, but the dimensions become much too large for manufacturing
Solution Approach 1:
The patent changes the fundamental operating parameters by switching from bulk acoustic waves to surface acoustic waves (Lamb waves). This parameter change enables the filter to achieve the same intermediate frequency filtering performance with dramatically reduced dimensions, making the filter manufacturable while maintaining the required filtering precision
Solution Approach 2:
The patent substitutes the mechanical resonance mechanism from bulk acoustic wave resonators to surface acoustic wave resonators. This substitution allows the filter to maintain its frequency-selective function while reducing the physical size from millimeter-scale to micrometer-scale dimensions
2Measurement precision
If the resonator dimensions are reduced to achieve narrow passband filtering, then the filtering precision improves, but the manufacturing precision requirements become much more stringent
Solution Approach 1:
By changing to surface acoustic wave resonance, the patent achieves narrow passband filtering with relaxed manufacturing tolerances. The surface wave nature provides inherent mode confinement that reduces sensitivity to dimensional variations, allowing narrow passbands to be achieved without proportionally stringent manufacturing precision requirements
Solution Approach 2:
The patent utilizes the surface dimension for wave propagation rather than bulk dimensions. This dimensional change creates natural boundary conditions that confine the acoustic energy to the surface region, reducing the impact of bulk dimension variations on the resonant frequency and passband characteristics
3Ease of manufacture
If conventional resonator configurations are used, then the filter can be manufactured, but the input/output impedances are very high (about several kohms)
Solution Approach 1:
The patent introduces intermediary transformation layers and electrode configurations that act as impedance transformers. These intermediaries match the high-impedance resonator output to the lower-impedance circuit board traces, enabling reliable signal transfer while maintaining the manufactability of the resonator structure
Solution Approach 2:
The patent merges the resonator structure with the interconnection architecture by integrating the electrodes and transmission lines directly with the resonator fabrication process. This merging reduces the number of separate components and interfaces, improving reliability while maintaining ease of manufacture through a unified fabrication approach
4Volume of moving object
If the filter is designed for direct IC integration, then the circuit size and costs are reduced, but the signal losses increase
Solution Approach 1:
The patent uses thin film piezoelectric layers deposited directly on the IC substrate to create the resonator structure. This thin film approach enables direct integration with minimal additional height while maintaining high quality factor resonance, reducing signal losses despite the integrated configuration
Solution Approach 2:
The patent creates a surface acoustic wave resonance phenomenon on the integrated circuit substrate that replicates the beneficial properties of discrete surface wave resonators. This copying of the resonance mechanism to the integrated platform achieves compact size without proportionally increasing signal losses
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 solution provides a narrow passband filter suitable for intermediate frequencies and channel filtering, reducing signal losses and costs while enabling direct integration onto an integrated circuit, achieving a passband of 1-2 MHz with reduced parasitic resonances and improved manufacturing feasibility.
Implementation Method 1
manufacture resonators using these Lamb waves
Implementation Method 2
the signal to be filtered is propagated vertically in stacked resonant layers
Implementation Method 3
BAW (Bulk Acoustic Wave) filters can be made from coupled bulk acoustic wave piezoelectric resonators
Implementation Method 4
The first and second resonant layers may be acoustically coupled by acoustic coupling means or by an acoustic coupler
Implementation Method 5
incorporating a Bragg mirror or periodic lattice to reduce parasitic resonances
Data Source
AI summary
A coupled Lamb wave resonator filter includes first and second Lamb wave resonators. The first Lamb wave resonator includes a first resonant layer, and first and second electrodes on opposite sides of the first resonant layer. The second Lamb wave resonator includes a second resonant layer, and third and fourth electrodes on opposite sides of the second resonant layer. One of the sides of the first resonant layer belongs to a plane parallel to a plane corresponding to one of the sides of the second resonant layer. Both planes pass through the third and fourth electrodes of the second Lamb wave resonator. A periodic lattice acoustically couples the first and second resonant layers.