Duplexer Filter Layout for Wider Attenuation Bandwidth
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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 transversal elastic wave filter, where the distance between interdigital transducers (IDTs) is set to 12λ or less, and optionally using slanted IDTs or varying electrode finger pitches, to achieve the same amplitude and opposite phase characteristics across a wider frequency range, thereby increasing attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a delay element is connected in parallel with a band pass filter, then attenuation at desired frequencies is increased, but the frequency range for which attenuation is effective remains narrow
Solution Approach 1:
The patent changes the physical parameters of the delay element by reducing the distance between IDTs to 12λ or less and using slanted IDT configurations. These parameter changes enable the delay element to provide opposite phase characteristics across a wider frequency range, thereby widening the frequency range for effective attenuation while maintaining high attenuation effectiveness at desired frequencies.
Solution Approach 2:
The patent introduces slanted IDTs that are inclined at an angle θ with respect to the propagation direction of surface acoustic waves. This dimensional change in the IDT configuration creates a frequency-dependent phase characteristic that varies with both frequency and angle, enabling broader frequency range coverage for attenuation while maintaining effectiveness across multiple frequency bands.
2Adaptability or versatility
If the distance between IDTs is reduced to 12λ or less, then the frequency range for increased attenuation is widened, but the device complexity increases
Solution Approach 1:
The patent optimizes the distance parameter between IDTs to 12λ or less, which is a specific quantitative parameter change. This parameter optimization achieves the dual benefit of widening the frequency range for attenuation while controlling device complexity through precise dimensional specification rather than complex structural arrangements.
Solution Approach 2:
The patent employs slanted IDTs with asymmetric inclination angles θ with respect to the wave propagation direction. This asymmetric configuration creates frequency-dependent phase characteristics that widen the effective attenuation frequency range without requiring multiple symmetric delay elements, thereby controlling overall device 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
This configuration effectively widens the frequency range for increased attenuation, improving signal isolation and reducing interference across multiple frequency bands, enhancing the performance of duplexer systems in mobile communication devices.
Implementation Method 1
the delay element is formed by a surface acoustic wave (SAW) filter of a transversal type
Implementation Method 2
a transversal elastic wave filter including a first IDT and a second IDT
Implementation Method 3
a transversal elastic wave filter including a first IDT and a second IDT, and a distance between the first IDT and the second IDT is 12λ or less when a wavelength determined by an electrode finger period of the IDT is denoted by λ
Implementation Method 4
The delay element has a characteristic that it has substantially the same amplitude characteristic but a phase that differs by (2n−1)π (n is a positive integer) at a desired frequency inside an attenuation range of the main filter. Therefore, direct waves at the desired frequency cancel each other out and attenuation can be increased at that frequency.
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.