Ladder Piezoelectric Filter With Parallel Ground Paths for Wide Bandwidth
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Solution Overview
Problem
Conventional piezoelectric filters face limitations in achieving wide bandwidth and high rejection requirements for advanced communication frequency bands, as increasing the electromechanical coupling coefficient is no longer effective in expanding application bandwidth.
Innovation Solution
A piezoelectric filter design with a special parallel ground path, incorporating additional resonators and inductors, which enlarges the relative bandwidth without altering the electromechanical coupling coefficient or manufacturing complexity, and includes impedance matching devices for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the electromechanical coupling coefficient is increased to expand bandwidth, then the bandwidth increases, but the manufacturing complexity and device structure become more complex
Solution Approach 1:
The filter is divided into multiple resonator units (first resonators in series path, second resonators in parallel path) with different configurations. Each resonator type serves a specific function: first resonators provide series resonance for passband formation, while second resonators with parallel ground connections provide additional bandwidth extension through controlled parallel resonance frequencies. This segmentation allows bandwidth expansion without requiring a single complex high-coupling resonator structure.
Solution Approach 2:
The patent extends the traditional single-path resonator structure into a multi-dimensional configuration by adding parallel ground paths with second resonators. This creates an additional dimension of bandwidth control through the parallel resonance frequency (fp) of second resonators, which is set lower than the series resonance frequency (fs) of first resonators. This dimensional extension enables bandwidth expansion without increasing the coupling coefficient of individual resonators.
2Ease of manufacture
If conventional ladder-type structure is used, then the filter design is simple, but the bandwidth is limited and cannot meet wideband communication requirements
Solution Approach 1:
The filter structure integrates multiple functions into a unified design: first resonators handle series resonance for basic passband operation, while second resonators with parallel ground connections simultaneously provide bandwidth extension and impedance control. The auxiliary inductors serve dual purposes of impedance matching and bandwidth enhancement. This multi-functional integration allows the filter to achieve wideband performance while maintaining a systematic design approach that builds upon conventional ladder structures.
Solution Approach 2:
Auxiliary inductors are introduced as intermediary elements that connect resonators to input/output terminals and provide impedance matching. These inductors mediate between the resonator structures and the external circuit, enabling optimal power transfer and bandwidth extension without requiring complex direct connections. The inductors act as tuning elements that adjust the overall filter response to achieve wideband performance.
3Adaptability or versatility
If bandwidth is expanded using conventional methods, then the application bandwidth increases, but the out-of-band rejection performance deteriorates
Solution Approach 1:
Different resonators are assigned different quality characteristics based on their positions and functions. First resonators in the series path are optimized for passband transmission with appropriate Q-factors, while second resonators in parallel paths are configured with specific parallel resonance frequencies (fp2 < fs1) to provide targeted stopband rejection. This local optimization of resonator characteristics allows bandwidth expansion while maintaining or enhancing out-of-band rejection at specific frequency regions, particularly at the low-frequency side of the passband.
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 filter achieves a bandwidth exceeding conventional limits by at least 20% with maintained out-of-band rejection, particularly at the low-frequency side, meeting high-performance requirements for wideband communications.
Implementation Method 1
the invention relates to the field of filtering devices for communication, and in particular, to a piezoelectric filter manufactured based on the principle of the piezoelectric effect
Implementation Method 2
Resonators constituting such acoustic wave filters mainly include a FBAR (Film Bulk Acoustic Resonator), a SMR (Solidly Mounted Resonators) and a SAW (Surface Acoustic Wave)
Data Source
AI summary
A wideband piezoelectric filter with a ladder-type is provided, which is composed of a plurality of first resonators connected in series, a plurality of second resonators connected in parallel, an impedance matching device disposed near the input terminal or the output terminal of the filter, and at least one special parallel ground path led out from serial nodes. The special parallel ground path at least comprises one inductor having a larger inductance value, and a resonator having the same resonant frequency as a serial branch or a capacitor, wherein the larger inductor is connected to the resonator or capacitor in series in the parallel path. The ladder filter according to the invention can have a bandwidth which is more than twice that of the conventional ladder filter, and also has excellent out-of-band rejection characteristics.