Acoustic Wave Filter Ladder Layout for Wider Pass Bands
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Solution Overview
Problem
In acoustic wave filter devices, widening the pass band of one band pass filter while maintaining low insertion loss is challenging due to the influence on the partner band pass filter, leading to increased return loss outside the pass band.
Innovation Solution
The design includes a first filter section with a ladder circuit and a second filter section, where the second filter section has a smaller fractional bandwidth, larger inductance values, and an inductor connected between the parallel arm resonator and the reference potential, while the first filter section lacks such an inductor, allowing for band widening and improved insertion loss in the partner filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an inductor is connected between a parallel arm resonator and the reference potential to widen the band of an acoustic wave filter, then the fractional bandwidth is improved, but the return loss outside the pass band increases causing worsened insertion loss in the pass band of the partner band pass filter
Solution Approach 1:
The patent applies local quality by differentiating the inductor configuration between the first and second band pass filters. The first filter includes an inductor connected between the parallel arm resonator and reference potential to widen its band, while the second filter deliberately omits this inductor. This localized differentiation allows each filter to have optimized characteristics for its specific function, resolving the contradiction between bandwidth expansion and insertion loss maintenance in partner filters.
2Adaptability or versatility
If the pass band of one band pass filter is widened by connecting an inductor, then the bandwidth is improved, but the filter characteristics of the partner band pass filter are influenced causing increased return loss
Solution Approach 1:
The patent extracts the inductor element from the second band pass filter while retaining it in the first filter. By removing (taking out) the inductor from the second filter's parallel arm resonator connection, the harmful influence on the partner filter's return loss is eliminated, while the first filter maintains its bandwidth-widening capability through the inductor.
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 widens the pass band while reducing return loss and improving insertion loss in the partner band pass filter, achieving better filter characteristics across the frequency range.
Implementation Method 1
the second filter section includes an inductor connected between at least the one parallel arm resonator and the reference potential
Implementation Method 2
a first filter section including a ladder circuit that includes at least one serial arm resonator and at least one parallel arm resonator wherein the serial arm resonator and the parallel arm resonator are each defined by an acoustic wave resonator
Data Source
AI summary
An acoustic wave filter device includes a second filter section connected to a first filter section. The second filter section includes acoustic wave resonators in a ladder circuit configuration. Of the acoustic wave resonators in the first and second filter sections, the acoustic wave resonator having the smallest fractional bandwidth is included in the second filter section. In the second filter section, inductors are respectively connected between parallel arm resonators and a reference potential. Attenuation near a pass band in the second filter section is larger than attenuation near a pass band in the first filter section.