Duplexer Reception Filter Impedance Matching
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Solution Overview
Problem
Existing balanced duplexers face challenges in achieving impedance matching and power handling performance, with reception filters either experiencing impedance mismatch or being damaged due to high power from transmission filters.
Innovation Solution
A balanced duplexer design incorporating a reception filter with a longitudinally-coupled-resonator type elastic wave filter, where the input terminal is connected in parallel to multiple IDTs, and the phase of output signals differs by 180 degrees between filter elements, ensuring a higher output impedance ratio and improved power handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a reception filter with 1:1 impedance ratio is used in a balanced duplexer, then power handling performance is improved, but impedance matching with subsequent stages cannot be achieved
Solution Approach 1:
The patent changes the impedance ratio parameter of the reception filter from the conventional 1:1 to a new ratio where output impedance is higher than input impedance. This parameter change enables both improved power handling performance and proper impedance matching with subsequent stages, resolving the technical contradiction between these two requirements.
2Reliability
If a reception filter with higher output impedance is used, then impedance matching with subsequent stages is achieved, but power handling performance deteriorates
Solution Approach 1:
The reception filter is segmented into multiple filter elements connected in parallel between the input terminal and output terminal. This segmentation allows the filter to achieve higher output impedance for better impedance matching while the parallel configuration maintains power handling capability by distributing the power load across multiple elements.
3Area of stationary object
If miniaturization is achieved by combining RF components, then device size is reduced, but complexity of impedance matching and power handling increases
Solution Approach 1:
The reception filter is designed with multi-functionality to simultaneously achieve impedance matching and power handling within a compact structure. By incorporating multiple filter elements with specific impedance ratios in parallel, the filter performs multiple functions (impedance transformation and power distribution) that would otherwise require separate components, thus reducing overall device size while managing 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
The design achieves easy impedance matching with subsequent stages and enhances power handling performance, preventing damage to the reception filter from transmission filter power, while reducing the duplexer's size and mounting area.
Implementation Method 1
a piezoelectric substrate, and a plurality of IDTs formed on the piezoelectric substrate
Implementation Method 2
an elastic wave filter device composed of a plurality of IDTs formed on a piezoelectric substrate
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
There is provided a duplexer with high power handling performance which includes a transmission filter having a ladder circuit configuration and a reception filter with a balanced-to-unbalanced conversion function and is capable of easily achieving the impedance matching between the reception filter and a circuit including a balanced input terminal connected to first and second reception output terminals of the reception filter and preventing the reception filter from being damaged due to electric power supplied from the transmission filter to the reception filter. A duplexer (1) includes a transmission filter (4) having a ladder circuit configuration and a reception filter (5). The reception filter (5) includes an input terminal (6) connected to an antenna terminal (3), a first reception output terminal (7), and a second reception output terminal (8). A first filter element (11) and a second filter element (12), each of which is a longitudinally coupled resonator filter element including a plurality of IDTs, are connected in parallel to the input terminal (6) so that IDTs (11a and 12a) are connected to the input terminal (6). The first filter element (11) and the second filter element (12) are connected to the first reception output terminal (7) and the second reception output terminal (8), respectively.