Parallel SAW Filter Design for Low Insertion Loss and High Attenuation
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Solution Overview
Problem
Existing surface acoustic wave filters connected in parallel face challenges in achieving both low insertion loss in the pass band and high attenuation in frequencies outside the pass band, as optimizing electrode film thickness can lead to impedance deviations and degraded insertion loss.
Innovation Solution
A filter design featuring a first surface acoustic wave filter connected between input and output nodes in series, with a second filter connected in parallel, having a greater number of interdigital transducer pairs and a specific aperture length product, to achieve reduced insertion loss and increased attenuation outside the pass band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If surface acoustic wave filters are connected in parallel to reduce insertion loss in the pass band, then insertion loss is improved, but attenuation in frequencies outside the pass band deteriorates
Solution Approach 1:
The patent applies local quality by making the two parallel filters have different electrode configurations. The first filter has N1 pairs of electrode fingers while the second filter has N2 pairs, with N1 > N2. This creates local differences in the electrode structure that allow each filter to contribute differently to the overall frequency response, enabling simultaneous improvement of insertion loss and maintenance of attenuation characteristics.
Solution Approach 2:
The patent employs asymmetry by designing the parallel-connected filters with unequal numbers of electrode finger pairs. The first filter has N1 pairs and the second filter has N2 pairs, where N1 > N2. This asymmetric configuration breaks the symmetry that would otherwise cause both filters to respond identically to all frequencies, allowing optimized performance across different frequency ranges including both pass band and stop band.
2Object-generated harmful factors
If the film thickness of electrodes is optimized to improve attenuation, then attenuation is improved, but impedance deviates from target value and insertion loss in the pass band degrades
Solution Approach 1:
The patent applies parameter changes by varying the number of electrode finger pairs (N1 and N2) between the two parallel filters rather than changing film thickness. This parameter adjustment allows optimization of attenuation characteristics while maintaining the impedance and insertion loss performance that would be compromised by film thickness optimization alone.
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 effectively reduces insertion loss while enhancing attenuation at frequencies outside the pass band, maintaining target impedance and improving filter performance.
Implementation Method 1
surface acoustic wave filters
Implementation Method 2
interdigital transducers
Data Source
AI summary
A filter includes a first filter that is connected between an input node and an output node and is a surface acoustic wave filter, and a second filter that is provided between the input node and the output node and is connected in parallel with the first filter. The first filter has a total number N1 of pairs of electrode fingers of interdigital transducers and the second filter having a total number N2 of pairs of electrode fingers of interdigital transducers, in which N1 is greater than N2.