Balanced Duplexer Reception Filter With Parallel IDTs
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Solution Overview
Problem
Existing balanced duplexers face challenges in achieving impedance matching between the reception filter and subsequent stages due to a 1:1 ratio of input impedance, leading to ripple in the passband, and have insufficient power handling performance, making them prone to damage from electric power from transmission filters.
Innovation Solution
A balanced duplexer with a reception filter featuring a balanced-to-unbalanced conversion function, utilizing a longitudinally coupled resonator elastic wave filter with a ratio of output impedance to input impedance greater than one, connected in parallel to improve power handling and prevent damage from transmission filter power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a reception filter with 1:1 input impedance ratio is used in a balanced duplexer, then the structure is simple, but impedance matching with subsequent stages cannot be achieved and ripple appears in the passband
Solution Approach 1:
The patent changes the impedance ratio parameter from 1:1 to a ratio greater than 1 (specifically achieving approximately 2:1 or higher) by modifying the IDT configuration and connection structure. This parameter change enables proper impedance matching with subsequent stages while eliminating passband ripple, directly resolving the contradiction between structural simplicity and impedance matching performance.
2Volume of stationary object
If a reception filter with low power handling performance is used, then the device size is small, but the filter is damaged by electric power from the transmission filter
Solution Approach 1:
The patent segments the reception filter into multiple IDTs (at least two IDTs) that are connected in parallel. This segmentation allows the input power to be distributed across multiple filter elements, increasing the overall power handling capability while maintaining a compact form factor. The segmented structure prevents any single IDT from being overloaded by the full transmission filter power.
Solution Approach 2:
The patent merges multiple IDTs in parallel configuration within the reception filter. By combining multiple filter elements with identical or complementary functions in parallel, the overall power handling capacity is increased while the physical footprint remains compact. This merging approach allows the reception filter to safely handle the electric power from the transmission filter without requiring a larger device size.
3Reliability
If multiple IDTs are connected in parallel in the reception filter, then power handling performance is improved, but the impedance ratio becomes greater than 1
Solution Approach 1:
The patent intentionally utilizes the parameter change that occurs when multiple IDTs are connected in parallel - specifically, the impedance ratio increases from 1:1 to greater than 1. Rather than viewing this as a worsening, the design embraces this parameter change as it enables proper impedance matching with subsequent stages. The parallel connection of multiple IDTs simultaneously achieves both improved power handling and appropriate impedance transformation.
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 ensures easy impedance matching and enhanced power handling performance, preventing damage to the reception filter while reducing the duplexer's size and maintaining low loss.
Implementation Method 1
an elastic wave filter device including a plurality of IDTs arranged on a piezoelectric substrate
Implementation Method 2
a plurality of IDTs arranged on a piezoelectric substrate
Implementation Method 3
longitudinally coupled resonator elastic wave filter
Data Source
AI summary
A duplexer includes a transmission filter having a ladder circuit configuration and a reception filter. The reception filter includes an input terminal connected to an antenna terminal, a first reception output terminal, and a second reception output terminal. A first filter element and a second filter element, each of which is a longitudinally coupled resonator filter element including a plurality of IDTs, are connected in parallel to the input terminal so that IDTs are connected to the input terminal. The first filter element the second filter element are connected to the first reception output terminal and the second reception output terminal, respectively.