Balanced Duplexer Reception Filter for Impedance Matching
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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 to output impedance, leading to ripple in the passband, and they suffer from insufficient power handling performance, which can result in damage from electric power supplied by the transmission filter.
Innovation Solution
A balanced duplexer with a reception filter using a 3-IDT longitudinally coupled resonator elastic wave filter, where the ratio of output impedance to input impedance is greater than one, and the input terminal is connected in parallel to multiple IDTs or elastic wave filter portions, ensuring phase matching between the transmission and reception filters without the need for additional phase matching elements, thereby improving power handling performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the reception filter uses a balanced-to-unbalanced conversion function with 1:1 impedance ratio, 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 from 1:1 to a value larger than one (e.g., 2:1 or higher) in the reception filter design. This parameter change enables both improved power handling performance and proper impedance matching with subsequent stages, resolving the technical contradiction by finding an optimal intermediate value that satisfies both requirements simultaneously.
2Reliability
If the reception filter is connected in parallel to multiple IDTs or elastic wave filter portions, then power handling performance is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple IDTs or elastic wave filter portions into a single integrated reception filter structure with parallel connections. This combining approach distributes power handling across multiple elements while maintaining a unified filter design, improving power handling performance without proportionally increasing overall device complexity.
3Volume of moving object
If the duplexer achieves miniaturization by combining RF stage components, then device size is reduced, but power handling performance deteriorates due to high power from transmission filters
Solution Approach 1:
The patent segments the reception filter into multiple parallel-connected IDTs or elastic wave filter portions, each capable of handling a portion of the total power. This segmentation allows the compact duplexer design to distribute power handling responsibilities, preventing any single element from being overwhelmed by high transmission filter power while maintaining miniaturization benefits.
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 enables easy impedance matching with subsequent stages, reduces ripple in the passband, and enhances power handling performance, preventing damage from electric power supplied by the transmission filter, resulting in a reliable and low-loss duplexer.
Implementation Method 1
a piezoelectric substrate with 3-IDT longitudinally coupled resonator elastic wave filter portions
Implementation Method 2
3-IDT longitudinally coupled resonator elastic wave filter portions
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A duplexer including a ladder-type transmission filter (4) and a reception filter (151) with a balanced-to-unbalanced conversion function can easily achieve impedance matching between the reception filter and a circuit including balanced input terminals connected to first and second reception output terminals (7,8) of the reception filter, and has high power handling performance. The reception filter includes first (154) and second (155) filter elements, each being a longitudinally-coupled-resonator filter element. The first elastic wave filter portion (154) includes second (154b), first (154a), and third (154c) IDTs, and the second elastic wave filter portion (155) includes fifth (155b), fourth (155a), and sixth (155c) IDTs. The first to sixth IDTs (154a-c,155a-c) are configured so that a phase difference between input and output signals in the first elastic wave filter portion (154) differs by 180 degrees from a corresponding phase difference in the second elastic wave filter portion (155). The first and fourth IDTs (154a,155a) are connected to the input terminal. The second and third IDTs (154b,154c) are connected in series and connected to the first reception output terminal (7), and the fifth and sixth IDTs (155b,155c) are connected in series and connected to the second reception output terminal (8).