SAW Multiplexer Circuit With High-Q Capacitor for Lower Insertion Loss
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Solution Overview
Problem
In multiplexers with multiple surface acoustic wave filters connected to a common antenna terminal, the filter characteristics of one filter are significantly affected by another, leading to increased insertion loss and size/cost due to bulk wave radiation losses, especially on the high-frequency side, without prior demultiplexing/multiplexing or phase-adjusting circuits.
Innovation Solution
Incorporating a capacitor with a higher Q value than the surface acoustic wave resonators in the second pass band between the common terminal and the first filter, which compensates for bulk wave radiation loss, thereby increasing the reflection coefficient and reducing insertion loss in the second pass band without the need for additional circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple surface acoustic wave filters are commonly connected to an antenna terminal to support multiple frequency bands, then the multiplexer supports multiple bands and modes, but the filter characteristic of one filter is greatly affected by the filter characteristic of another filter, leading to increased insertion loss
Solution Approach 1:
The patent segments the common connection path by inserting a segmentation inductor between the antenna terminal and the first filter. This inductor electrically separates the filters while maintaining their common connection, reducing mutual interference and insertion loss in each filter's pass band.
Solution Approach 2:
The segmentation inductor acts as an intermediary element between the antenna terminal and the filters. It mediates the interaction between multiple filters by providing impedance transformation and reducing the direct coupling effect that causes insertion loss.
2Loss of energy
If demultiplexing/multiplexing devices or phase-adjusting circuits are arranged in stages prior to the filters to counteract filter characteristic interference, then the insertion loss is reduced, but the multiplexer is increased in size and cost
Solution Approach 1:
The patent extracts the phase adjustment function from separate demultiplexing/multiplexing devices and integrates it directly into the first filter through the segmentation inductor. This eliminates the need for additional standalone phase-adjusting circuits, reducing device complexity while maintaining low insertion loss.
Solution Approach 2:
The patent merges the phase adjustment function with the first filter by strategically placing the segmentation inductor in series with the first filter. This combination achieves both filtering and phase adjustment in a single integrated structure, avoiding additional components.
3Reliability
If the return loss seen from the antenna terminal side of one filter is increased in the pass band of another filter, then the reflection characteristic of one filter is improved, but the insertion loss in the pass band of the other filter is increased
Solution Approach 1:
The patent changes the electrical parameters of the connection path by introducing the segmentation inductor with specific inductance value. This parameter adjustment optimizes the impedance matching and reduces the harmful interaction between filters, simultaneously improving reflection characteristics and reducing 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 reduces high-frequency signal propagation loss and minimizes size and cost by enhancing the reflection coefficient and reducing insertion loss in the second pass band, while maintaining compactness and low cost.
Implementation Method 1
a capacitor that is serially arranged on a connection path between the common terminal and the first filter. A Q value of the capacitor in the second pass band is higher than a Q value in the second pass band of a capacitance obtained when treating the at least one surface acoustic wave resonator as a capacitance.
Implementation Method 2
a first filter that is formed of at least one surface acoustic wave resonator arranged between the common terminal and the first input/output terminal
Data Source
AI summary
A multiplexer (1) includes a plurality of filters connected to a common terminal (110). The multiplexer (1) includes: a low-frequency filter (11L) that is formed of at least one surface acoustic wave resonator arranged between the common terminal (110) and the input/output terminal (120) and has a first pass band; a high-frequency filter (12H) that is connected between the common terminal (110) and the input/output terminal (130) and has a second pass band located at a higher frequency than the first pass band; and a capacitor (CB1) that is serially arranged in a connection path between the common terminal (110) and the low-frequency filter (11L). The Q value of the capacitor (CB1) in the second pass band is higher than the Q value in the second pass band of a capacitance obtained by treating the at least one surface acoustic wave resonator of the low-frequency filter (11L) as a capacitance.