Acoustic Wave Ladder Filter Topology for Interference Band Rejection
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Solution Overview
Problem
Existing filter devices for cellular phones, which are multi-band and multi-mode, face limitations in attenuation characteristics outside the pass band, leading to potential radio wave interference with other communication devices due to insufficient attenuation poles.
Innovation Solution
The implementation of a filter device with a first and second acoustic wave resonator positioned on the lower or higher frequency side of the pass band, creating an attenuation band that overlaps with a predetermined frequency band to increase insertion loss, and optionally using a second ladder filter with an attenuation pole or band to enhance attenuation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitors are connected in parallel to predetermined ones of the serial resonators and the parallel resonators, then the attenuation pole can be adjusted, but the number of attenuation poles that can be formed is limited and attenuation characteristics in predetermined frequency bands are insufficient
Solution Approach 1:
The invention divides the filter structure into multiple ladder filters, each capable of forming attenuation poles independently. By segmenting the filter into first and second ladder filters with separate resonator configurations, the system can generate multiple attenuation poles across different frequency bands, overcoming the limitation of a single ladder filter structure.
Solution Approach 2:
The invention nests multiple ladder filters within a single filter device, where the first ladder filter and second ladder filter are integrated together. This nesting approach allows the filter device to contain multiple attenuation pole-forming structures, enabling sufficient attenuation characteristics across predetermined frequency bands while maintaining a compact overall structure.
2Object-affected harmful factors
If more attenuation poles are added to improve attenuation characteristics in predetermined frequency bands, then radio wave interference is reduced, but the device complexity and number of components increase
Solution Approach 1:
Each ladder filter in the invention is designed to serve multiple functions: filtering signals in the pass band and simultaneously forming attenuation poles in predetermined frequency bands. The resonators in each ladder filter contribute to both the main filtering function and the attenuation characteristics, allowing a single component to perform multiple roles and reducing the need for additional dedicated attenuation components.
Solution Approach 2:
The invention merges the attenuation pole-forming function with the main filter structure by integrating capacitors into the resonator configurations of the ladder filters. This combining approach allows attenuation poles to be generated as part of the normal filter operation without requiring separate, additional components, thereby reducing overall device complexity while achieving sufficient attenuation of radio wave interference.
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 significantly improves attenuation characteristics in predetermined frequency bands outside the pass band, reducing radio wave interference and enhancing the filter's ability to prevent interference with other communication devices.
Implementation Method 1
a resonance point and an anti-resonance point of the first acoustic wave resonator are both positioned on the lower frequency side or the higher frequency side of a pass band of the first ladder filter
Implementation Method 2
a resonance point and an anti-resonance point of the second acoustic wave resonator are both positioned on the lower frequency side or the higher frequency side of the pass band of the first ladder filter and on the same side as the side in which the resonance point and the anti-resonance point of the first acoustic wave resonator are positioned
Data Source
AI summary
A filter device includes a first ladder filter including serial resonators disposed in a terminal-to-terminal path and parallel resonators disposed in connection paths, a first acoustic wave resonator disposed in parallel to the parallel resonator, and a second acoustic wave resonator disposed in parallel to the serial resonator. Resonance points and anti-resonance points of the first and second acoustic wave resonators are both positioned on the lower frequency side or the higher frequency side of a pass band of the first ladder filter, and on the same side of the pass band of the first ladder filter, when viewed from the pass band of the first filter.