Duplexer Filter Layout for Wider Stopband Attenuation
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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.
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 12λ or less, and optionally featuring slanted IDTs or varying electrode finger pitches, to achieve the same amplitude and opposite phase characteristics across a wider frequency range.
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 appropriate phase shifts across a wider frequency range, thereby widening the frequency range over which attenuation is effective while maintaining attenuation effectiveness at desired frequencies.
Solution Approach 2:
The patent introduces dynamic characteristics by using slanted IDTs that create frequency-dependent phase shifts. This dynamic behavior allows the delay element to adapt its phase response across different frequencies, enabling effective attenuation across a broader frequency range rather than at a single fixed frequency.
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 dimensions are reduced
Solution Approach 1:
The patent deliberately changes the distance parameter between IDTs to 12λ or less, which is a specific parameter optimization that achieves the dual benefit of widening the frequency range for attenuation while maintaining a compact device length. This parameter change is the core of the invention that resolves the apparent contradiction between frequency range and device size.
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
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 includes a transversal elastic wave filter including a first IDT and a second IDT
Implementation Method 2
The delay element includes 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 3
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.