Parallel SAW Filter Duplexer 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 passbands 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 maintains the same amplitude and opposite phase characteristics as the band pass filter, 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 desired frequencies, then attenuation at specific frequencies 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 fundamentally alters the phase characteristic across frequency. This parameter change enables the delay element to maintain opposite phase relationship with the band pass filter over a wider frequency range, thereby widening the frequency range for effective attenuation while maintaining reliable attenuation performance at desired frequencies
2Adaptability or versatility
If the distance between IDTs in a delay element is reduced to 12λ or less, then the frequency range for increased attenuation is widened, but the device structure becomes more compact with tighter spacing requirements
Solution Approach 1:
The patent explicitly sets the distance parameter between IDTs to 12λ or less (preferably 6λ or less) to achieve the desired phase characteristic. This parameter optimization allows the delay element to maintain opposite phase relationship across a wider frequency range, effectively widening the attenuation frequency range while accepting the compact dimension as a necessary design trade-off for achieving broader frequency coverage
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 signal isolation and reducing interference in mobile communication devices by maintaining close to opposite phases across a wide frequency range, thereby improving attenuation by up to 10 dB in specific bands.
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.