Elastic Wave Filter Layout for Wider Out-of-Band Attenuation
Find Innovative SolutionsGenerate Solutions
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, 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 for 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 and enables the delay element to provide opposite phase over a wider frequency range, thereby resolving the contradiction between maintaining reliable attenuation and expanding the applicable frequency range
Solution Approach 2:
The patent introduces a slanted or inclined finger configuration for the IDTs, adding a spatial dimension (angle) to the traditional parallel finger structure. This dimensional change modifies the wave propagation characteristics and phase response, enabling broader frequency range attenuation while maintaining the core function of the delay element
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 effectively widens the frequency range for increased attenuation, achieving up to 17 MHz of frequency range for opposite phases compared to 8 MHz in existing technologies, and provides improved out-of-band attenuation across a broader spectrum.
Implementation Method 1
the delay element is formed by a surface acoustic wave (SAW) filter of a transversal type
Implementation Method 2
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
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
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.