Acoustic Wave Ladder Filter With Bridged-T Upper Band Edge Sharpening
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Solution Overview
Problem
Conventional acoustic wave resonator ladder filters struggle to achieve a very sharp upper passband edge, which is necessary for certain applications, as they fail to provide a sufficient transition from high transmission to high attenuation within a small frequency range proximate the upper limit of the passband.
Innovation Solution
Incorporating a bridged-T circuit configuration into the filter design, where capacitors are used to connect identical acoustic wave resonators in series and shunt configurations, effectively altering the anti-resonance frequencies and sharpening the upper band edge by reducing the anti-resonance frequency without significantly changing the resonance frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional acoustic wave resonator ladder filters are used, then the filter structure is simple, but the upper band edge sharpness is insufficient
Solution Approach 1:
The filter structure is segmented into multiple identical acoustic wave resonators arranged in series and shunt configurations. Each resonator is designed with specific resonance and anti-resonance frequencies, and their collective arrangement creates the desired sharp upper band edge transition while maintaining modular simplicity
Solution Approach 2:
The invention changes the frequency parameters of the acoustic wave resonators by adjusting their physical dimensions and material properties. Specifically, resonators are designed with anti-resonance frequencies positioned above the passband to create the sharp upper band edge, while resonance frequencies are positioned within the passband to maintain low insertion loss
2Manufacturing precision
If the passband transmission is maintained at high levels, then the insertion loss is reduced, but the upper band edge transition becomes less sharp
Solution Approach 1:
The invention utilizes mechanical vibration principles through acoustic wave resonators that exhibit strong resonance at specific frequencies. By positioning the resonance frequencies within the passband and anti-resonance frequencies above the passband, the resonators naturally amplify signals within the passband (maintaining low insertion loss) while providing sharp attenuation at the upper band edge
Solution Approach 2:
The Q-factor and frequency parameters of the resonators are carefully adjusted to achieve the desired balance. Higher Q-factor resonators provide sharper transitions, while their resonance frequencies are positioned to ensure minimal insertion loss within the passband, creating an optimized trade-off between transmission efficiency and edge sharpness
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 bridged-T circuit significantly improves the sharpness of the upper band edge transition, achieving a steep drop from high transmission to low transmission, as demonstrated by simulation results showing a transition from -1 dB to less than -27 dB within a 15 MHz frequency span, enhancing the filter's ability to meet specific application requirements.
Implementation Method 1
acoustic wave resonators... exhibit both a resonance and an anti-resonance
Implementation Method 2
acoustic wave resonators... exhibit both a resonance and an anti-resonance
Implementation Method 3
surface acoustic wave resonators (SAWs)
Implementation Method 4
bulk acoustic wave (BAW) resonators
Implementation Method 5
film bulk acoustic wave (FBAW) resonators
Data Source
AI summary
Bandpass filters are disclosed. A bandpass filter includes a plurality of series resonators and a plurality of shunt resonators. The series resonators are connected in series between a first port and a second port. The plurality of series resonators includes a first series resonator and a second series resonator connected at a node. The plurality of shunt resonators includes a first shunt resonator coupled between the node and a ground. A capacitor bridges the first and second series resonators.