RF Multiplexer Filter Layout for Lower Intermodulation Distortion
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Solution Overview
Problem
Multiplexers with acoustic wave filters suffer from deterioration in reception sensitivity due to intermodulation distortion (IMD) caused by the non-linear elastic constant of acoustic wave resonators, particularly in scenarios where multiple frequency bands are used, leading to reduced performance in signal transmission.
Innovation Solution
The multiplexer design incorporates a configuration with a common terminal and three filters, where the first and second filters have non-overlapping passbands, and the third filter has a passband overlapping with frequencies generated by the first two, utilizing a higher combined capacitance in the parallel arm resonance circuit compared to the serial arm resonance circuits to mitigate IMD, thereby reducing current density and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If acoustic wave resonators are used in filters to enable multiple frequency bands, then the multiplexer can transmit signals in a plurality of frequency bands, but intermodulation distortion occurs due to non-linear elastic constant, deteriorating reception sensitivity
Solution Approach 1:
The patent applies local quality by making the parallel arm resonance circuit have different characteristics (higher combined capacitance) compared to serial arm resonance circuits. Specifically, the parallel arm resonance circuit uses acoustic wave resonators with higher capacitance values to reduce current density and minimize intermodulation distortion, while serial arm circuits use lower capacitance resonators. This localized differentiation in resonator properties allows the filter to simultaneously support multiple frequency bands while suppressing IMD in the reception band.
Solution Approach 2:
The patent changes the capacitance parameter of acoustic wave resonators based on their position in the filter circuit. By setting the combined capacitance of parallel arm resonators higher than that of serial arm resonators, the patent optimizes the current distribution to reduce intermodulation distortion. This parameter change approach allows the same type of component (acoustic wave resonator) to serve different functions in different circuit locations, maintaining multi-band capability while improving reception sensitivity.
2Adaptability or versatility
If the number of filters is increased to support more frequency bands, then the multiplexer handles more bands, but insertion loss increases
Solution Approach 1:
The patent implements universality by designing filters that can operate in multiple frequency bands simultaneously. The first and second filters are configured with passbands that do not overlap, allowing them to handle different frequency bands without interference. The common terminal and shared acoustic wave resonators enable these filters to work together efficiently, reducing the need for separate dedicated filters for each band and thereby minimizing cumulative insertion loss while supporting multiple frequency bands.
3Measurement precision
If acoustic wave resonators with non-linear elastic constant are used, then the filter provides frequency selectivity, but intermodulation distortion occurs when two transmission signals are present
Solution Approach 1:
The patent converts the harmful non-linear effect into a beneficial outcome by strategically placing higher-capacitance acoustic wave resonators in the parallel arm configuration. The non-linear elastic constant of acoustic wave resonators inherently generates intermodulation distortion, but by positioning resonators with optimized (higher) capacitance values in the parallel arm circuit, the patent directs the current flow to minimize IMD generation in the reception band. This transforms the unavoidable non-linear property into a controllable characteristic that serves the overall system performance.
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 suppresses the deterioration of reception sensitivity by lowering current density in the parallel arm resonator, thereby reducing distortion and improving signal reception across multiple frequency bands.
Implementation Method 1
an acoustic wave resonator
Implementation Method 2
A combined capacitance of the first parallel arm resonance circuit is higher than a minimum value of a combined capacitance of each of the at least one first serial arm resonance circuit
Data Source
AI summary
A multiplexer includes a common terminal, a first terminal, a second terminal, and a third terminal, a first filter, a second filter, and a third filter. With a frequency f3 being defined as M×f1±N×f2 or M×f2±N×f1, M and N being natural numbers, f1 being a frequency included in a first passband of the first filter and f2 being a frequency included in a second passband of the second filter, at least a part of a range of frequency f3 overlaps a third passband of the third filter. No acoustic wave resonator is connected between the common terminal and a first parallel arm resonance circuit. A combined capacitance of the first parallel arm resonance circuit is higher than a minimum value of a combined capacitance of each of at least one first serial arm resonance circuit.