Parallel SAW Filter Layout for Wider Attenuation Bands
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Solution Overview
Problem
Existing filter devices in mobile communication devices have a narrow frequency range for increasing attenuation outside of passbands, limiting their effectiveness in mobile communication devices where frequency widths between channels are decreasing.
Innovation Solution
A filter device with a band pass filter connected in parallel to a delay element, specifically a transversal elastic wave filter with a distance of 12λ or less between IDTs, which provides the same amplitude and opposite phase characteristics, effectively widening the frequency range for increased attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a delay element is connected in parallel with a band pass filter to increase attenuation at a desired frequency, then attenuation at that frequency is improved, but the frequency range across which attenuation is increased remains narrow
Solution Approach 1:
The patent changes the physical parameter of the delay element by reducing the distance between IDTs to 12λ or less, which modifies the phase characteristic across a broader frequency range. This parameter change enables the delay element to provide opposite phase characteristics over a wider bandwidth, thereby widening the frequency range for increased attenuation while maintaining effective attenuation at desired frequencies
Solution Approach 2:
The patent introduces a slanted or inclined finger configuration for the IDTs, adding a geometric dimension to the delay element structure. This dimensional change creates a transversal elastic wave filter that achieves both wide bandwidth attenuation and maintains the required phase opposition characteristics across multiple frequency bands
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 significantly widens the frequency range across which attenuation is increased, enhancing the filter's performance by achieving higher attenuation across a broader range of frequencies, as demonstrated by the comparison of transmission and reception characteristics.
Implementation Method 1
the delay element is formed by a surface acoustic wave (SAW) filter of a transversal type
Implementation Method 2
direct waves at the desired frequency cancel each other out and attenuation can be increased at that frequency
Implementation Method 3
a delay element that is connected in parallel with the band pass filter and has a same amplitude characteristic as and an opposite phase of the band pass filter at a desired frequency inside an attenuation range of the band pass filter. The delay element preferably includes a transversal elastic wave filter
Data Source
AI summary
In a filter device, a transversal elastic wave filter, which defines a delay element, is connected in parallel with a band pass filter. The transversal elastic wave filter has the same amplitude characteristic as and the opposite phase to the band pass filter at a desired frequency inside an attenuation range of the band pass filter. When a wavelength determined by an electrode finger period of IDTs and is denoted by λ, the distance between the first IDT and the second IDT of the elastic wave filter is about 12λ or less.