Multimode SAW Filter Layout for Precise Attenuation Pole Tuning
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Solution Overview
Problem
Existing multimode filters with inductors connected between IDTs and ground experience large changes in attenuation pole frequencies with inductance adjustments, making it difficult to achieve desired attenuation characteristics on the low-frequency side of the passband.
Innovation Solution
A filter design where an inductor is connected to two or more and half or less IDTs, including at least one input and one output IDT, with the other IDTs connected directly to ground, allowing for controlled frequency adjustments of the attenuation pole.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an inductor is connected between all IDTs and ground, then the frequency of the attenuation pole on the high-frequency side can be adjusted, but the frequency of the attenuation pole on the low-frequency side changes significantly and it becomes difficult to adjust the desired attenuation characteristics
Solution Approach 1:
The patent segments the IDTs into two groups: those connected to the inductor and those connected directly to ground. Specifically, the inductor is connected to only a portion of the IDTs (either a specific number or a specific position), while other IDTs are connected directly to ground. This segmentation allows independent control of the attenuation poles, enabling precise adjustment of the high-frequency attenuation pole through the inductor without significantly affecting the low-frequency attenuation pole.
Solution Approach 2:
The patent applies local quality by creating different connection configurations for different portions of the IDTs. The IDTs connected to the inductor have different electrical characteristics compared to those connected directly to ground. This local differentiation allows the inductor to specifically influence the high-frequency attenuation pole while leaving the low-frequency attenuation pole relatively unaffected, thereby achieving precise frequency adjustment without compromising low-frequency attenuation characteristics.
2Adaptability or versatility
If inductance is adjusted to change attenuation pole frequency, then frequency adjustment is achieved, but the amount of change is large making fine adjustment difficult
Solution Approach 1:
By connecting the inductor to only a portion of the IDTs rather than all IDTs, the patent segments the influence of the inductor on the attenuation poles. This segmentation reduces the overall impact of inductance changes on the attenuation pole frequencies, enabling finer and more precise frequency adjustment. The segmented connection allows for gradual tuning of the high-frequency attenuation pole without causing excessive shifts in frequency.
3Measurement precision
If an inductor is connected to multiple IDTs, then the attenuation pole frequency can be adjusted, but the complexity of the circuit increases
Solution Approach 1:
The patent simplifies the circuit complexity by segmenting which IDTs are connected to the inductor. Instead of requiring complex interconnections, the inductor is connected to a specific, limited portion of the IDTs (either a predetermined number or a specific positional group). This segmented approach maintains straightforward circuit configuration while achieving effective attenuation pole frequency control.
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 enables precise adjustment of attenuation pole frequencies and improved attenuation characteristics on the low-frequency side of the passband with reduced variations in loss and ripple, enhancing filter performance.
Implementation Method 1
an inductor having a first end, which is connected to two or more and half or less IDTs of the input IDTs and the output IDTs, and a second end connected to a ground
Implementation Method 2
a multimode filter in which a plurality of interdigital transducers (IDTs) are arranged in a propagation direction of a surface acoustic wave (SAW)
Implementation Method 3
a multimode filter provided on the piezoelectric substrate, the multimode filter including input IDTs and output IDTs
Data Source
AI summary
A filter includes a piezoelectric substrate, a multimode filter provided on the piezoelectric substrate, the multimode filter including input IDTs and output IDTs, the input IDTs being connected to an input terminal, the output IDTs being connected to an output terminal and arranged alternately with the input IDTs, and an inductor having a first end, which is connected to two or more and half or less IDTs of the input IDTs and the output IDTs, and a second end connected to a ground, the two or more and half or less IDTs including at least one input IDT of the input IDTs and at least one output IDT of the output IDTs.