Elastic-Wave Ladder Filter Layout for Wider Passbands With Lower Loss
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Solution Overview
Problem
Existing surface-acoustic-wave ladder filters in cellular phones face challenges in extending passbands, increasing attenuation, and reducing loss, particularly in high frequency regions within the passband, due to diffraction loss affecting antiresonance characteristics.
Innovation Solution
The elastic-wave ladder filter design includes series arm resonators with varying resonant frequencies, where the aspect ratio of the resonator with the lowest resonant frequency is larger than the average, and the resonator with the highest resonant frequency has a smaller aspect ratio, optimizing electrode finger overlap and number of pairs to reduce loss and enhance attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the resonant frequencies of series arm resonators are made different from each other to extend passbands and increase attenuation, then the passband width and attenuation are improved, but the loss within the passband particularly in high frequency region is increased
Solution Approach 1:
The patent applies local quality by assigning different aspect ratios to different series arm resonators based on their specific resonant frequencies. The resonator with the lowest resonant frequency is given a larger aspect ratio than average, while the resonator with the highest resonant frequency is given a smaller aspect ratio than average. This localized optimization of aspect ratios for different resonators compensates for the increased loss in high frequency regions, allowing the passband to be extended without suffering from excessive loss.
2Loss of energy
If the overlap width of electrode fingers is reduced and the number of pairs is increased to reduce electrical resistance, then electrical resistance and loss are reduced, but diffraction loss is increased which affects antiresonance characteristics
Solution Approach 1:
The patent applies parameter changes by optimizing the aspect ratio parameter for each series arm resonator based on its resonant frequency characteristics. By changing the aspect ratio parameter locally for different resonators (larger for lowest frequency, smaller for highest frequency), the patent achieves a balance between reducing electrical resistance and maintaining antiresonance characteristics, preventing excessive diffraction loss while keeping ohmic loss low.
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 configuration effectively reduces loss within the passband, particularly in high frequency regions, while increasing passband width and attenuation, by improving return loss and antiresonance characteristics.
Implementation Method 1
surface-acoustic-wave filters have been widely used as band-pass filters of cellular phones for RF stages
Implementation Method 2
the resonant frequency frs of series arm resonators and the antiresonant frequency fap of parallel arm resonators are set adjacent to the central frequency in a passband
Implementation Method 3
loss caused by diffraction of surface acoustic waves is increased when the overlap width is extremely reduced
Data Source
AI summary
An elastic-wave ladder filter significantly reduces loss within a passband while also increasing the passband and attenuation. The elastic-wave ladder filter includes a series arm that connects an input end and an output end and a parallel arm that connects the series arm and a ground potential. The series arm includes at least three series arm resonators connected to each other in series. The resonant frequencies of the at least three series arm resonators differ from each other. An aspect ratio of the series arm resonator having the lowest resonant frequency is larger than an average of the aspect ratios of all the series arm resonators when the aspect ratio is defined as a ratio of an overlap width of electrode fingers of a series arm resonator to a number of pairs of the electrode fingers.