Mirror-Connected Ladder Filter With Unequal Terminal Impedance
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Solution Overview
Problem
Ladder filters in RF stages of cellular phones face challenges with impedance matching, leading to increased loss and footprint due to the need for multiple impedance matching devices when peripheral components have impedances different from the standard 50Ω.
Innovation Solution
A ladder filter design with multiple serial and parallel arm resonators, where ladder circuit units are mirror-connected and have varying impedances, reducing the need for multiple impedance matching devices by allowing impedance differences between the input and output terminals, and using a single inductor for impedance matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If impedance matching circuits with multiple devices are used to match peripheral components with non-50Ω impedance, then impedance matching is achieved, but loss increases and footprint becomes large
Solution Approach 1:
The patent changes the impedance parameters of the ladder filter terminals, allowing one terminal to have 50Ω impedance while the other has different impedance. This parameter change enables direct connection to peripheral components without requiring multiple impedance matching devices, thereby reducing loss while maintaining effective impedance matching where needed.
Solution Approach 2:
The patent extracts and eliminates the impedance matching circuit from the overall system by designing the ladder filter terminals with appropriate impedances directly. Instead of adding separate matching circuits, the filter itself is designed to provide the necessary impedance characteristics, removing the need for additional matching devices and reducing overall loss.
2Reliability
If impedance matching circuits with multiple devices are used to match peripheral components with non-50Ω impedance, then impedance matching is achieved, but footprint becomes large
Solution Approach 1:
The patent changes the impedance parameters of the ladder filter terminals, allowing one terminal to have 50Ω impedance while the other has different impedance. This parameter change enables direct connection to peripheral components without requiring multiple impedance matching devices, thereby reducing footprint while maintaining effective impedance matching where needed.
Solution Approach 2:
The patent merges the impedance matching function into the ladder filter structure itself by designing terminals with specific impedance values. The filter and impedance matching functions are combined into a single integrated structure, eliminating the need for separate matching circuits and reducing overall footprint.
3Device complexity
If all ladder circuit units have equal impedance, then impedance matching is simplified, but the ability to match different peripheral impedances is limited
Solution Approach 1:
The patent applies local quality by making the impedance characteristics of different ladder circuit units non-uniform. Specifically, adjacent ladder circuit units have different impedance values, allowing the filter to adapt to different peripheral component impedances at different locations while maintaining overall system performance.
Solution Approach 2:
The patent introduces asymmetry in the impedance values of adjacent ladder circuit units. Instead of uniform impedance throughout, the design uses asymmetric impedance distribution where neighboring units have different impedance values, enabling versatile impedance matching while managing complexity through systematic design.
Data Source
AI summary
A ladder filter includes serial arm resonators disposed along a serial arm and parallel arm resonators disposed along corresponding parallel arms. Ladder circuit units are disposed along a path from an input terminal, which is a first end, to an output terminal, which is a second end. Each of the ladder circuit units includes a single serial arm resonator and a single parallel arm resonator. The ladder circuit units are mirror-connected to one another. The impedance at the first end is different from the impedance at the second end.