LC and Acoustic Wave Filter Layout for IMD Suppression
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Solution Overview
Problem
Acoustic wave resonators exhibit nonlinear distortion and inferior intermodulation distortion (IMD) characteristics when used in communication systems operating within the 3 GHz to 4 GHz band, leading to potential degradation of receiving sensitivity and non-compliance with communication standards, especially in dual connectivity scenarios and simultaneous operations with LTE and wireless LAN bands.
Innovation Solution
A filter circuit configuration is implemented, where an LC filter is placed closer to the antenna terminal to attenuate out-of-band signals, thereby suppressing IMD generated by acoustic wave resonators, while maintaining a wide-band transmission characteristic. This configuration includes a first filter with an LC circuit for a pass band and a second filter using an acoustic wave resonator for attenuation of specific frequency bands, ensuring steepness from the pass range to the attenuation range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If acoustic wave resonators are used to achieve steep attenuation characteristics, then the steepness from pass range to attenuation range is improved, but intermodulation distortion increases and receiving sensitivity degrades
Solution Approach 1:
The filter circuit is divided into two separate filter sections: a first filter using acoustic wave resonators to provide steep attenuation characteristics, and a second filter using an LC circuit to provide wide-band transmission and reduce intermodulation distortion. This segmentation allows each filter to perform its specialized function without compromising the other.
Solution Approach 2:
The LC circuit filter acts as an intermediary between the antenna terminal and the acoustic wave resonator filter. It pre-filters wide-band signals and reduces intermodulation distortion before signals reach the acoustic wave resonators, thereby protecting the resonators from generating excessive distortion while still allowing the resonators to provide their steep attenuation characteristics.
2Measurement precision
If acoustic wave resonators with higher energy density are designed for 3 GHz to 4 GHz band, then frequency selectivity is improved, but distortion increases
Solution Approach 1:
The filtering function is segmented between two different technologies: LC circuits handle wide-band frequency selection with low distortion, while acoustic wave resonators provide steep attenuation at specific frequency bands. This allows high frequency selectivity without the penalty of high distortion.
Solution Approach 2:
The LC circuit serves as an intermediary that performs initial frequency selection and signal conditioning before signals reach the acoustic wave resonators. This reduces the burden on the resonators and minimizes the distortion they generate while maintaining their frequency selectivity advantages.
3Reliability
If LC filter is used for wide-band transmission, then transmission characteristic is improved, but attenuation steepness deteriorates
Solution Approach 1:
The filter circuit is segmented into two functional sections: the LC circuit filter provides wide-band transmission characteristics with low intermodulation distortion, while the acoustic wave resonator filter provides steep attenuation characteristics. Each section excels at its designated function.
Solution Approach 2:
The patent merges two different filter technologies (LC circuits and acoustic wave resonators) into a single integrated filter circuit. The LC circuit section handles wide-band transmission, while the acoustic wave resonator section provides steep attenuation, creating a composite filter that achieves both wide-band transmission and steep attenuation characteristics simultaneously.
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 suppresses IMD at acoustic wave resonators, maintains wide-band transmission characteristics, and ensures compliance with communication standards by securing steepness from the pass range to the attenuation range, particularly in the 3 GHz to 6 GHz band, allowing for selective attenuation of frequency bands like Band n77 and Band n79.
Implementation Method 1
a second filter that attenuates at least part of one of a second frequency band (n77) and a third frequency band (n79) using an attenuation pole produced by a resonance or an antiresonance of an acoustic wave resonator
Implementation Method 2
a first filter including an LC circuit in which a first frequency band is a pass band and a frequency band not higher than the first frequency band is an attenuation band
Data Source
AI summary
A filter circuit that secures the steepness from a pass range to an attenuation range while maintaining a wide-band transmission characteristic and a filter device including this filter circuit are formed. A filter circuit includes a first filter and a second filter. The first filter is a filter including an LC circuit in which a first frequency band is a pass band and a frequency band not higher than the first frequency band is an attenuation band. The second filter is a filter that attenuates a second frequency band within the first frequency band by using an attenuation pole produced by a resonance or an antiresonance of an acoustic wave resonator. Further, the first filter is placed closer to an antenna terminal than the second filter.