Elastic Wave Filter Common-Connection High-Order Mode Interference
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Solution Overview
Problem
Existing elastic wave filter devices experience increased insertion loss in the pass band of a reception filter when a high-order mode, such as Sezawa waves, is excited and positioned within the pass band of the reception filter, due to common-connection with a transmission filter.
Innovation Solution
The elastic wave filter device incorporates a first filter with a serial arm resonator or a longitudinally coupled resonator-type filter on the common connection point side, where the resonant frequency of the high-order mode is set to be lower than the second filter's pass band, using a configuration that includes a serial arm resonator with a non-highest resonant frequency or a parallel arm resonator with a non-lowest resonant frequency to reduce interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If one end of a transmission filter and one end of a reception filter are common-connected, then the filter device can be compact and share a common connection point, but the high-order mode generated in the transmission filter affects the filter characteristics of the reception filter, causing increased insertion loss
Solution Approach 1:
A mode separation filter is introduced as an intermediary component between the transmission filter and reception filter at the common connection point. This filter selectively passes the fundamental wave while blocking the high-order mode, thereby separating the unwanted mode from the reception filter input and preventing it from degrading reception filter characteristics
Solution Approach 2:
The high-order mode is extracted and removed from the signal path using the mode separation filter. By identifying and separating the harmful high-order mode component from the fundamental wave, the invention eliminates the source of interference before it can affect the reception filter
2Speed
If the resonant frequency of the high-order mode is positioned within the pass band of the reception filter, then the filter can operate at higher frequencies, but insertion loss in the reception filter pass band becomes large
Solution Approach 1:
The mode separation filter serves as a mediator that allows the reception filter to operate at higher frequencies while preventing the high-order mode from reaching it. The filter selectively blocks the high-order mode frequency components while passing the desired fundamental wave, enabling high-frequency operation without the penalty of increased insertion loss
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 configuration effectively reduces insertion loss in the pass band of the second filter by distancing the resonant frequency of the high-order mode from the second filter's pass band, thereby minimizing signal loss.
Implementation Method 1
an element closest to a common connection point is a serial arm resonator. A pass band of the reception filter is set to be higher than a pass band of the transmission filter... the first filter includes, on the common connection point side, a serial arm resonator including an IDT (interdigital transducer) electrode
Implementation Method 2
The transmission filter of the elastic wave filter device described in Japanese Unexamined Patent Application Publication No. 2015-111845 makes use of Rayleigh waves propagating in LiNbO3
Implementation Method 3
a serial arm resonator in which the resonant frequency is not the highest, (2) a parallel arm resonator, or (3) a longitudinally coupled resonator-type elastic wave filter, is provided
Data Source
AI summary
In an elastic wave filter device, a first filter including a first pass band and a second filter including a second pass band are common-connected at a common connection point. The first filter includes, on the common connection point side, a serial arm resonator, a parallel arm resonator, or a longitudinally coupled resonator-type elastic wave filter, and generates a fundamental wave and a high-order mode. A resonant frequency of the high-order mode on a higher frequency side relative to the first pass band of the first filter is smaller than the second pass band. On the common connection point side, a serial arm resonator in which the resonant frequency is not the highest, a parallel arm resonator, or a longitudinally coupled resonator-type elastic wave filter, is disposed.