Ladder Filter Circuit With Grounded Resonator Pole Shifting
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Solution Overview
Problem
Existing filter devices face challenges in adjusting the attenuation pole generated by sub-resonance to the lower frequency side without increasing the device size, particularly for Wi-Fi communication, as increasing capacitance complicates reducing the device's size.
Innovation Solution
Incorporating a first path with a ladder filter circuit and a second path connected in parallel, featuring a grounded resonator and a capacitor that adjusts the attenuation pole by generating a cancel signal with inverted phase, allowing the attenuation pole to be shifted to the lower frequency side without enlarging the device.
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 attenuation pole frequency is reduced, but the device size increases
Solution Approach 1:
The patent divides the capacitance function into two separate components: the original parallel arm resonator and an additional capacitor connected in series. This segmentation allows the capacitance value to be adjusted by changing the series capacitor rather than increasing the size of the resonator itself, thereby shifting the attenuation pole frequency without increasing device volume.
Solution Approach 2:
The patent introduces a series capacitor as an intermediary element between the parallel arm resonator and ground. This intermediary component enables frequency adjustment of the attenuation pole without requiring changes to the resonator's physical dimensions, thus resolving the contradiction between frequency control and size reduction.
2Reliability
If a loop circuit is added in parallel with the ladder filter circuit to improve isolation characteristics, then isolation characteristics are improved, but device complexity increases
Solution Approach 1:
The patent combines the isolation improvement function with the existing parallel arm resonator structure by adding a series capacitor to it. Instead of creating a separate loop circuit, the invention merges the frequency adjustment and isolation functions into a single modified resonator branch, thereby improving isolation characteristics while minimizing the increase in device complexity.
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 effectively shifts the attenuation pole to the lower frequency side while maintaining a compact filter device size, enhancing isolation characteristics and reducing signal leakage between frequency bands.
Implementation Method 1
featuring a grounded resonator and a capacitor that adjusts the attenuation pole by generating a cancel signal with inverted phase
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.