Elastic Wave Tunable Filter for Wider Passband Stability
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Solution Overview
Problem
Tunable filters in communication systems face challenges with small electromechanical coupling coefficients and frequency-temperature coefficients, limiting the adjustability and stability of passband filters.
Innovation Solution
A tunable filter design incorporating an elastic wave resonator with a piezoelectric substrate, such as LiNbO3 or LiTaO3, and a bandwidth extending inductance, along with variable capacitors and matching elements, to enhance the electromechanical coupling coefficient and reduce frequency-temperature coefficients, allowing for adjustable passband width and improved temperature characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If surface acoustic wave resonators are used in tunable filters, then the filter can be tuned by varying capacitor values, but the electromechanical coupling coefficient remains small and the frequency-temperature coefficient is small, limiting performance
Solution Approach 1:
The patent changes the fundamental parameter of the resonator type from surface acoustic wave resonators to elastic wave resonators. This parameter change directly addresses the contradiction by providing a resonator with inherently larger electromechanical coupling coefficient and frequency-temperature coefficient, thereby improving reliability while maintaining tunability through capacitor variation
Solution Approach 2:
The patent employs composite material structure by combining elastic wave resonators with variable capacitors in a ladder filter circuit. This composite approach leverages the high coupling coefficient of elastic wave resonators while using variable capacitors to provide tunability, thus resolving the contradiction between adaptability and reliability
2Adaptability or versatility
If the passband width is increased, then the frequency variable range is improved, but the temperature characteristics become less stable
Solution Approach 1:
The patent changes the resonator parameter from surface acoustic wave type to elastic wave type, which fundamentally alters the temperature characteristics. Elastic wave resonators exhibit larger frequency-temperature coefficients that can be better controlled and compensated, allowing the passband width to be increased while maintaining stable temperature characteristics
Solution Approach 2:
The patent utilizes the inherent frequency-temperature coefficient of elastic wave resonators in a controlled manner. By selecting resonators with appropriate temperature coefficients and combining them with variable capacitors, the system achieves feedback-like compensation where temperature drift can be managed while maintaining wide passband and frequency variable range
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 increases the passband width and frequency variable range while maintaining stable temperature characteristics, enabling more precise control over the filter's frequency response.
Implementation Method 1
the resonator circuit portion includes an elastic wave resonator and a bandwidth extending inductance connected to the elastic wave resonator, the elastic wave resonator including a piezoelectric substrate, which includes LiNbO3 or LiTaO3, and an electrode located on the piezoelectric substrate
Data Source
AI summary
A tunable filter that is capable of magnifying a pass band width or increasing a frequency variable amount includes a resonator circuit portion provided in at least one of a series arm connecting an input terminal and an output terminal to each other and a parallel arm connecting the series arm and a ground potential to each other, a first variable capacitor is connected in series to the resonator circuit portion and a second variable capacitor is connected in parallel to the resonator circuit portion. The resonator circuit portion includes a piezoelectric substrate including LiNbO3 or LiTaO3, an elastic wave resonator including an electrode located on the piezoelectric substrate, and a bandwidth extending inductance Lx, Lx connected to the elastic wave resonator.