Ladder SAW Filter Additional Pole for SH Mode Suppression
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Solution Overview
Problem
SAW filters with compensation layers face reduced coupling, leading to parasitic SH mode propagation that causes interference and premature wear, especially in broadband filters and front-end modules handling multiple frequency bands.
Innovation Solution
A SAW filter with a ladder-type structure incorporating additional resonators connected in parallel to series resonators, allowing for capacitive tuning at the center frequency and shifting the interfering SH mode out of the passband range, while maintaining bandwidth and insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a compensation layer is added to reduce temperature response, then temperature stability is improved, but coupling is reduced
Solution Approach 1:
The patent changes the physical parameters of the resonators by adding an additional resonator with specific resonance and anti-resonance frequencies. This allows tuning the filter's frequency response to compensate for the coupling reduction caused by the temperature stability layer, thereby maintaining both temperature stability and coupling performance.
Solution Approach 2:
The filter employs a composite structure combining multiple resonators with different electrical characteristics (series and parallel resonators with varying Q-factors and frequency responses). This composite approach allows the system to achieve both temperature stability through the compensation layer and adequate coupling through the resonator network configuration.
2Object-affected harmful factors
If filter geometry is optimized for maximum SH mode suppression, then SH mode interference is reduced, but manufacturing precision requirements increase due to tolerance-related geometric deviations
Solution Approach 1:
The additional resonator acts as an intermediary element that provides frequency-selective filtering. By introducing a resonator with specifically designed anti-resonance frequency, the system can suppress SH modes through electrical filtering rather than relying solely on precise geometric optimization, thereby reducing the stringency of manufacturing tolerance requirements.
Solution Approach 2:
The patent changes the electrical parameters of the filter by adding a resonator with tailored resonance and anti-resonance frequencies. This allows suppression of SH modes through frequency domain filtering rather than geometric optimization, making the system more robust to manufacturing variations while maintaining effective SH mode rejection.
3Measurement precision
If additional resonators are added to improve attenuation at disturbance frequencies, then selectivity is improved, but device complexity increases
Solution Approach 1:
The filter is segmented into functionally distinct resonators: series resonators for passband formation and parallel resonators for stopband enhancement. Each resonator is optimized for its specific function, allowing the system to achieve high frequency selectivity through modular design while keeping individual component complexity low.
Solution Approach 2:
The additional parallel resonators serve multiple functions: they provide attenuation at disturbance frequencies, maintain passband characteristics, and can be tuned to suppress specific interference frequencies. This multi-functionality allows a single additional component to address multiple performance requirements without proportionally increasing overall system 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 solution effectively suppresses interfering frequencies and shifts the SH mode above the passband edge, enhancing the performance of SAW filters by improving attenuation and reducing thermal stress without compromising passband characteristics.
Implementation Method 1
The pitch of this additional resonator is dimensioned to be capacitive at the center frequency of the filter, but forms with its anti-resonance at an interfering frequency an additional pole for improved attenuation of the interference frequency.
Implementation Method 2
forms with its anti-resonance at an interfering frequency an additional pole for improved attenuation
Implementation Method 3
The resonance frequency of the acoustic Rayleigh mode is used on this substrate material.
Implementation Method 4
The resonance frequency of the acoustic Rayleigh mode is used on this substrate material.
Implementation Method 5
In order to reduce the temperature response of SAW filters, they are provided with a compensation layer—typically comprising SiO2.
Data Source
AI summary
In order to suppress an interference frequency in a ladder-type filter, an additional resonator (RZ1) that acts as a capacitance is connected in parallel to a series resonator (S1). The antiresonance of the additional resonator creates an additional pole in order for the interference frequency to be attenuated more effectively.