Acoustic Wave Filter IDT Capacitance Tuning for Lower Insertion Loss
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Solution Overview
Problem
Acoustic wave filter devices face challenges in maintaining impedance for signals outside the pass band while minimizing insertion loss, as increasing inductance to adjust phase leads to increased resistive components and degraded bandpass characteristics.
Innovation Solution
The acoustic wave filter device incorporates a longitudinally coupled resonator with IDT electrodes, where the total capacitance or intersecting area of the input-side IDT electrodes is greater than that of the output-side IDT electrodes, reducing the inductance and resistive component of the series inductor, thereby maintaining impedance without increasing insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inductance of the series inductor is increased to adjust phase, then the phase of reflection characteristics approaches that of an open state, but the insertion loss increases due to increased resistive component
Solution Approach 1:
The patent changes the capacitance parameters of IDT electrodes to achieve impedance matching. Specifically, the first IDT electrode has a larger capacitance value than the second IDT electrode, which allows the system to achieve the desired phase characteristics without requiring high inductance values that would increase insertion loss.
Solution Approach 2:
Instead of using a series inductor to achieve impedance matching (conventional approach), the patent inverts the approach by using capacitive elements (IDT electrodes with different capacitance values) to achieve the same goal. This inversion allows impedance matching without the harmful resistive effects of high-inductance components.
2Ease of operation
If a series inductor is used for impedance matching, then the phase adjustment is achieved, but the resistive component increases degrading bandpass characteristics
Solution Approach 1:
The patent changes from inductive parameter adjustment to capacitive parameter adjustment. By setting the capacitance of the first IDT electrode larger than that of the second IDT electrode, the system achieves phase adjustment through capacitive reactance rather than inductive reactance, thereby avoiding the resistive losses associated with high-inductance components.
Solution Approach 2:
The patent substitutes the mechanical/physical inductor component with an equivalent electrical function achieved through capacitive elements. The series inductor is replaced by a capacitive divider formed by IDT electrodes with different capacitance values, achieving the same phase adjustment function without the harmful resistive component.
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 maintains impedance for signals outside the pass band while reducing insertion loss, improving the bandpass characteristics of the acoustic wave filter device.
Implementation Method 1
at least one first IDT electrode coupled to the first terminal, and at least one second IDT electrode connected to the second terminal
Implementation Method 2
acoustic wave filter device including a longitudinally coupled resonator
Data Source
AI summary
An acoustic wave filter device includes first and second terminals, an inductor connected to the first terminal, and a longitudinally coupled resonator coupled between the inductor and the second terminal. The longitudinally coupled resonator includes at least one first IDT electrode coupled to the first terminal, and at least one second IDT electrode connected to the second terminal. A total capacitance value of the at least one first IDT electrode is greater than a total capacitance value of the at least one second IDT electrode.