Ladder Filter Circuit With Capacitive Path for Lower Attenuation Pole
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Solution Overview
Problem
Existing filter devices struggle to shift the attenuation pole generated by sub-resonance to the lower frequency side without increasing the device size, particularly in wireless communication apparatuses like cellular phones, due to the need to adjust the capacitance of parallel arm resonators.
Innovation Solution
Incorporating a capacitor-connected second path in parallel with the ladder filter circuit, which includes a grounded resonator and a capacitor, allows for adjusting the attenuation pole without increasing the device size by providing additional parameters for generating a cancel signal with inverted phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the capacitance of a parallel arm resonator is increased to shift the attenuation pole to the lower frequency side, then the frequency adjustment is achieved, but the device size increases making it difficult to reduce the filter device size
Solution Approach 1:
The invention divides the capacitance function into two separate components: the original parallel arm resonator capacitance and an additional capacitor connected in the third path. This segmentation allows independent optimization - the resonator maintains its original size while the additional capacitor provides the necessary capacitance value to shift the attenuation pole frequency without increasing the resonator's physical dimensions.
Solution Approach 2:
The invention introduces a third path as an intermediary element that connects the parallel arm resonator to the ground terminal through an additional capacitor. This intermediary path enables frequency adjustment by adding capacitance in series with the resonator, achieving attenuation pole shifting without modifying the resonator's physical structure or increasing overall device size.
2Reliability
If a loop circuit is disposed in parallel with the ladder filter circuit to improve isolation characteristics, then the isolation between frequency bands is enhanced, but the device complexity increases
Solution Approach 1:
The invention merges the isolation function with the existing ladder filter circuit structure by adding the third path and capacitor in parallel with the parallel arm resonator. This integration achieves improved isolation characteristics without requiring a separate loop circuit, thereby reducing device complexity while maintaining the desired isolation performance between frequency bands.
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 shifts the attenuation pole to the lower frequency side, enhancing signal isolation and reducing the likelihood of signal leakage between frequency bands without enlarging the filter device.
Implementation Method 1
a parallel arm resonator in a ladder filter circuit generates an attenuation pole by utilizing sub-resonance formed in a radio-frequency band
Implementation Method 2
One end of the capacitor is connected to the second path, and the other end of the capacitor is connected to a third path which connects the parallel arm resonator and the ground terminal
Data Source
AI summary
A filter device includes a first path, a second path, and a capacitor. The first path includes at least one ladder filter circuit and connects a first terminal and a second terminal. The at least one ladder filter circuit includes a parallel arm resonator connected to a ground terminal. The second path includes a grounded resonator and is connected in parallel with any of the at least one ladder filter circuit. One end of the capacitor is connected to the second path, and the other end of the capacitor is connected to a third path which connects the parallel arm resonator and the ground terminal.