Ladder Filter Impedance Matching for Low-Loss Multiplexers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-frequency filters and multiplexers face challenges in impedance matching between components with different input/output impedances, leading to increased complexity and insertion loss when trying to match the impedance from a low-noise amplifier (LNA) to a common terminal or antenna, which requires complex matching elements and larger filter sizes.
Innovation Solution
A high-frequency ladder filter design with series and parallel arm resonators, where the parallel arm resonator closest to the LNA has the highest anti-resonant frequency, functions as an inductive element in the pass band, allowing for impedance matching with a less complex matching element by adjusting the impedance viewed from the LNA terminal to be higher than from the antenna terminal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a complex matching element is used to match impedance between LNA and common terminal, then impedance matching is improved, but device complexity and filter size increase
Solution Approach 1:
The patent changes the impedance parameter distribution within the filter by making the impedance viewed from the LNA terminal higher than the impedance viewed from the common terminal. This is achieved by configuring the ladder filter with specific series arm resonators and parallel arm resonators where the parallel arm resonators have anti-resonant frequencies higher than the passband frequencies, creating an inductive effect that raises the input impedance. This parameter change eliminates the need for external complex matching elements.
Solution Approach 2:
The filter structure itself provides the impedance matching function through its internal configuration. The parallel arm resonators with anti-resonant frequencies above the passband automatically generate an inductive effect that raises the input impedance to match the LNA, making the filter self-matching and eliminating the need for separate matching components.
2Reliability
If a complex matching element is used to match impedance between LNA and common terminal, then impedance matching is improved, but insertion loss increases
Solution Approach 1:
By changing the impedance parameter distribution within the filter structure itself, the patent eliminates the need for external matching elements that would introduce additional insertion loss. The internal configuration of parallel arm resonators with high anti-resonant frequencies provides both impedance matching and low loss performance simultaneously.
3Reliability
If impedance as viewed from LNA terminal is made higher than from antenna terminal, then impedance matching with LNA is improved, but matching element complexity increases
Solution Approach 1:
The patent achieves higher impedance at the LNA terminal by configuring parallel arm resonators with anti-resonant frequencies higher than the passband frequencies. This creates an inductive effect that naturally raises the input impedance to match the LNA's higher input impedance requirement, all within the filter structure itself without external matching elements.
Solution Approach 2:
The filter structure autonomously provides the higher impedance at the LNA terminal through its internal resonator configuration, making the system self-matching and eliminating the need for additional matching components that would increase 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 design reduces the complexity of matching elements and filter size while maintaining low insertion loss and improving impedance matching between the LNA and other components, achieving optimal impedance characteristics for both the LNA and antenna terminals.
Implementation Method 1
the first parallel arm resonator connected closest to the second input/output terminal has the highest anti-resonant frequency
Implementation Method 2
the first parallel arm resonator is closest to the second input/output terminal and most significantly influences the impedance as viewed from the second input/output terminal of the high-frequency filter. Also, since having the highest anti-resonant frequency of the at least two parallel arm resonators, the first parallel arm resonator defines and functions as an inductive element in most portions of the pass band of the high-frequency filter
Implementation Method 3
an inductor connected in series to the at least one series arm resonator, the inductor being closer to the first input/output terminal than the at least one series arm resonator and the at least two parallel arm resonators are to the first input/output terminal
Implementation Method 4
at least one series arm resonator connected in a path between a first input/output terminal and a second input/output terminal; at least two parallel arm resonators each connected between a connection node in the path and a ground
Data Source
AI summary
A ladder filter includes at least one series arm resonator connected in a path between first and second input/output terminals, at least two parallel arm resonators each connected between a connection node in the path and a ground, and an inductor connected in series to the at least one series arm resonator. The inductor is closer to the first input/output terminal than are the at least one series arm resonator and the at least two parallel arm resonators. Of the at least two parallel arm resonators, a first parallel arm resonator connected closest to the second input/output terminal has the highest anti-resonant frequency.