Acoustic Wave Multiplexer Impedance Matching With Shunt Capacitance
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Solution Overview
Problem
In multiplexers supporting multiple bands, achieving impedance matching and low insertion loss is challenging due to the insertion loss caused by series inductors used for impedance adjustment, especially when larger inductance values are required.
Innovation Solution
Incorporating a capacitance element between the signal path and ground electrode of an acoustic wave filter with a parallel resonator, which allows for impedance adjustment using a smaller inductance value and improves return loss by moving impedance positions on a Smith chart, thereby achieving better impedance matching and reducing insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a series inductor is used for impedance adjustment in a multiplexer, then impedance matching in the pass band is improved, but insertion loss increases
Solution Approach 1:
The patent changes the impedance adjustment approach by introducing a shunt capacitor connected between the signal path and ground, rather than using a series inductor. This parameter change in the circuit configuration allows for impedance matching without the insertion loss penalty associated with series inductors, as the capacitor provides a different impedance transformation mechanism that preserves signal energy.
Solution Approach 2:
The shunt capacitor acts as an intermediary element that mediates the impedance matching between the acoustic wave filter and the common terminal. By providing an alternative current path to ground, the capacitor enables impedance transformation without requiring a series inductor that would directly impede the signal path and cause insertion loss.
2Measurement precision
If a larger inductance value is used in the series inductor for impedance adjustment, then impedance matching is improved, but insertion loss increases
Solution Approach 1:
The patent fundamentally changes the circuit parameter by replacing the series inductor configuration with a shunt capacitor configuration. This parameter change eliminates the direct relationship between inductance value and insertion loss, as the capacitor provides impedance matching through a different physical mechanism that does not introduce series resistance losses.
3Adaptability or versatility
If multiple acoustic wave filters are connected at a common terminal, then multi-band functionality is achieved, but impedance matching becomes difficult
Solution Approach 1:
The patent applies local quality by introducing individual shunt capacitors at specific locations within the multiplexer circuit, particularly at the common terminal where multiple acoustic wave filters converge. This localized impedance adjustment allows each filter connection point to be optimized independently, enabling multi-band functionality while maintaining accurate impedance matching at each frequency band.
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 enables accurate impedance matching and low-loss properties in multiplexers, reducing the need for larger inductance values and minimizing unnecessary wave outflow from high-order modes.
Implementation Method 1
a first capacitance element connected between a signal path between the one end of the parallel resonator and the inductance element, and a ground electrode
Implementation Method 2
the first acoustic wave filter includes a parallel resonator of which one end is connected to the first input/output terminal and another end is connected to a ground electrode
Implementation Method 3
the first input/output terminal being connected to the common terminal via the inductance element
Data Source
AI summary
A multiplexer includes a common terminal, a first acoustic wave filter having a first frequency band as a pass band, and having a first input/output terminal connected to the common terminal, a second acoustic wave filter having a second frequency band higher than the first frequency band as a pass band, and having a second input/output terminal connected to the common terminal, an inductance element, and a first capacitance element. The first acoustic wave filter has a parallel resonator of which one end is connected to the first input/output terminal and another end is connected to a ground electrode, and the first input/output terminal is connected to the common terminal via the inductance element, and the first capacitance element is connected between a signal path between the one end of the parallel resonator and the inductance element, and a ground electrode.