Balanced SAW Band-Elimination Filter With Steep Cutoff
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Solution Overview
Problem
Conventional band elimination filters for mobile communication devices, particularly those using surface acoustic wave (SAW) elements, face challenges in achieving balanced input and output with a reduced number of configuration elements and a steep cut-off characteristic to filter out the one-segment broadcast frequency band without interfering with WCDMA transmission signals.
Innovation Solution
A novel band elimination filter structure featuring balanced input and output with a minimal number of elements, including at least one resonator connected in series between input and output terminals and an impedance element connected between these terminals, allowing for compact design and steep cut-off characteristics using acoustic wave elements like SAW, BAW, or FBAR resonators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional ladder-type band elimination filter is used, then the filter can eliminate the WCDMA transmission signal band, but the input and output terminals are unbalanced requiring additional converters
Solution Approach 1:
The patent applies asymmetry by using different configurations for the signal path (series resonators) and reference path (parallel resonators with impedance elements). This asymmetric structure enables balanced input and output terminals while maintaining the band elimination function, resolving the contradiction between balanced terminals and structural simplicity.
2Reliability
If a ladder-type filter with balanced input and output is used, then balanced terminals are achieved, but the number of resonator elements becomes large reducing compactness
Solution Approach 1:
The patent merges the functions of multiple resonators by configuring them in series and parallel combinations. The signal path uses series resonators while the reference path uses parallel resonators with impedance elements, combining multiple functions into a compact structure that maintains balanced terminals with fewer elements.
Solution Approach 2:
The filter structure achieves multi-functionality by using the same basic resonator and impedance element configurations for both signal path and reference path. This universal approach allows the filter to provide band elimination, balanced input/output, and compact size simultaneously.
3Measurement precision
If the cut-off characteristic is made steep to separate one-segment broadcast from WCDMA signals, then signal separation is improved, but filter complexity increases
Solution Approach 1:
The patent applies local quality by concentrating the steep cut-off characteristic generation in specific locations: series resonators in the signal path and parallel resonators with impedance elements in the reference path. This localized approach achieves precise frequency separation without requiring complex structures throughout the entire filter.
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 enables a compact filter device with balanced input and output, achieving a steep cut-off characteristic that effectively filters out the one-segment broadcast frequency band while minimizing interference from WCDMA signals, and allows for miniaturization and high resonance Q values.
Implementation Method 1
a filter device constituted of an acoustic wave element such as a surface a coustic wave (SAW) element having a resonance characteristic in the VHF and UHF bands
Implementation Method 2
SAW element having a resonance characteristic
Data Source
AI summary
A filter device has a novel structure, satisfying requirements to have balanced input and output, with a small number of configuration elements. The above filter device includes first and second balanced signal terminals on the input side to be connected to an external balance circuit; first and second balanced signal, terminals on the output side to be connected to an external balance circuit; at least one first resonator connected in series between the first balanced signal terminal on the input side and the first balanced signal terminal on the output side; at least one second resonator connected in series between the second balanced signal terminal on the input side and the second balanced signal terminal on the output side; and at least one impedance element connected between the first balanced signal terminal on the output side and the second balanced signal terminal on the input side.