Cascaded Monolithic Crystal Filter for Anharmonic Mode Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current monolithic crystal filters are limited to low frequencies due to fabrication difficulties, resulting in high insertion loss and poor out-of-band rejection at high frequencies, making it challenging to extend their application into the GHz range while effectively suppressing anharmonic modes.
Innovation Solution
A cascaded monolithic crystal filter design is implemented, where the first filter includes two resonators with electrodes featuring tabs or cut-outs that selectively shift anharmonic modes, and a second filter is acoustically coupled to enhance out-of-band rejection without affecting the fundamental mode, allowing for improved frequency suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single mode quartz filter is used to achieve good out-of-band rejection at low frequency, then the filter dimension becomes smaller than a few microns with a gap of 1 micron or less at high frequency, making fabrication error tolerance costly and difficult to attain
Solution Approach 1:
The filter is divided into multiple resonators (first resonator and second resonator) that are acoustically coupled. This segmentation allows each resonator to be larger in dimension while maintaining the overall compact filter size, thereby improving fabrication error tolerance without sacrificing high-frequency performance
Solution Approach 2:
The patent employs a nested structure where resonators are arranged in a cascaded configuration with acoustic coupling between them. This nested arrangement enables the filter to achieve high out-of-band rejection through multiple resonant stages while keeping the overall footprint compact, resolving the contradiction between small size and manufacturing precision
2Manufacturing precision
If conventional processing is used for high frequency filters, then the suppression of anharmonic modes becomes critical but difficult to achieve, resulting in poor out-of-band rejection
Solution Approach 1:
The patent introduces specific structural features (such as electrode periphery modifications) on individual resonators that locally affect anharmonic mode frequencies. These localized quality changes shift anharmonic modes away from the passband without requiring complex conventional processing, thereby improving anharmonic mode suppression while maintaining ease of manufacture
Solution Approach 2:
The patent changes the physical parameters of the resonators (such as electrode geometry and acoustic coupling characteristics) to selectively suppress anharmonic modes. By adjusting these parameters, the filter achieves high out-of-band rejection through fundamental mode resonance while pushing anharmonic modes to unwanted frequency regions, resolving the contradiction between manufacturing precision and ease of manufacture
3Manufacturing precision
If low frequency MCF design is used, then good out-of-band rejection of about 60 dB is achieved, but insertion loss increases to 6-7 dB
Solution Approach 1:
The patent employs dynamically coupled resonators where the acoustic coupling between the first and second resonators is optimized to achieve sharp roll-off characteristics. This dynamic coupling allows the filter to achieve high out-of-band rejection (greater than 60 dB) while maintaining low insertion loss through resonant enhancement in the passband, resolving the contradiction between out-of-band rejection and insertion loss
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 design achieves high out-of-band rejection of up to 80 dB with low insertion loss, enabling the creation of high-performance GHz filters with minimal size and power consumption, suitable for wireless communication applications.
Implementation Method 1
An input voltage signal at 110 is coupled to the output 120 by acoustical coupling through the piezoelectric material 130
Implementation Method 2
The filter has a second resonator acoustically coupled to the first resonator
Data Source
AI summary
In one embodiment, a cascaded monolithic crystal filter is provided. A first filter includes two resonators having a pair of electrodes with the monolithic crystal between. At least one electrode has a periphery which includes a feature capable of shifting a frequency associated with an anharmonic mode in the filter. The filter has a second resonator acoustically coupled to the first resonator. A second filter is cascaded with the first filter. The second filter includes a pair of acoustically coupled resonators.