Acoustic Wave Filter Phase Shifting for Lower Return Loss
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Solution Overview
Problem
Acoustic wave filters using Shear Horizontal (SH) waves face issues with widened pass bands and increased insertion loss due to bulk waves in high-frequency ranges, leading to signal leakage and worsened return loss, making it difficult to achieve desired filter characteristics in duplexers and similar devices.
Innovation Solution
Incorporating a first phase-shift element, such as an inductor, and a second phase-shift element, such as a capacitor, between the common terminal and the filters, which allows the impedance to be adjusted closer to the outermost constant conductance circle in a Smith chart, reducing return loss and insertion loss by optimizing the phase and impedance matching across different pass bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If an SH wave is used to widen the pass band, then the pass band width is improved, but the return loss deteriorates due to bulk wave generation in high-frequency ranges
Solution Approach 1:
A phase-shift element is introduced as an intermediary component between the filter and the common terminal. This phase-shift element modifies the impedance characteristics in the high-frequency range, preventing bulk wave generation while maintaining the widened pass band. The phase-shift element acts as a mediator that transforms the impedance to reduce signal leakage to other filters.
2Area of moving object
If the pass band is widened using an SH wave, then the filter characteristic is improved, but signal leakage to other filters increases
Solution Approach 1:
The phase-shift element serves as an intermediary that prevents signal leakage by transforming the impedance characteristics. It is positioned between the filter and the common terminal to control the signal flow and prevent unwanted coupling between filters with adjacent pass bands.
3Loss of energy
If impedance matching is optimized for the pass band, then the insertion loss is reduced, but the return loss in high-frequency ranges deteriorates
Solution Approach 1:
The phase-shift element introduces local impedance transformation specifically in the high-frequency range. By adjusting the phase shift characteristics of this element, the impedance is optimized locally to prevent bulk wave generation and improve return loss without affecting the pass band insertion loss.
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 reduces signal leakage and insertion loss, improving the return loss and bandpass characteristics of filters with higher pass bands, allowing for wider pass bands and better impedance matching, thus enhancing the performance of acoustic wave devices and radio-frequency front-end circuits.
Implementation Method 1
the phase of an impedance when a first-terminal side is viewed from a branch-point side is easily caused to approach close to an outermost constant conductance circle in a Smith chart
Implementation Method 2
an SH (Shear Horizontal) wave that indicates a relatively large electromechanical coupling coefficient as compared to other types of acoustic waves is used as a propagation mode
Implementation Method 3
a bulk wave is caused in a particular frequency range on the high-pass-band side with respect to the pass band of the filter
Data Source
AI summary
An acoustic wave device includes a common terminal, a first terminal, a second terminal, a first filter, a second filter, and an inductor. The first filter has a pass band corresponding to a relatively low frequency range and includes a surface acoustic wave filter using an SH wave. The second filter has a pass band corresponding to a relatively high frequency range. The first filter is between a branch point and the first terminal on a path connecting the common terminal and the first terminal. The second filter is between the branch point and the second terminal on a path connecting the common terminal and the second terminal. The inductor is on a path connecting the branch point and the first filter.