RF Multiplexer Capacitor Layout for Low-Band Insertion Loss
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Solution Overview
Problem
Existing multiplexers for cellular phones experience increased insertion loss in the pass band of low-frequency filters due to spurious signals generated by high-frequency filters, which can degrade the performance of radio-frequency signals.
Innovation Solution
A multiplexer design with a second capacitor having a higher Q value than the first pass band, connected between the common terminal and the high-frequency filter, to increase the Q value of the capacitance of the high-frequency filter, thereby reducing the insertion loss and reflection coefficient in the pass band of the low-frequency filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a high-frequency filter is connected to a common terminal in a multiplexer, then the filter can process high-frequency signals, but spurious signals are generated that overlap with the pass band of low-frequency filters, degrading insertion loss
Solution Approach 1:
A capacitor is introduced as an intermediary component between the common terminal and the high-frequency filter. This capacitor acts as a mediator that selectively affects different frequency ranges: it presents low impedance to high-frequency signals (allowing them to pass) while presenting high impedance to low-frequency spurious signals (blocking them from entering the high-frequency filter and contaminating the low-frequency pass band), thereby resolving the contradiction between multi-band adaptability and insertion loss degradation
2Adaptability or versatility
If multiple filters are connected to a common terminal to handle multiple frequency bands, then the multiplexer can support multiple modes, but the Q value of the capacitance in the first pass band is insufficient, leading to increased insertion loss
Solution Approach 1:
The capacitor is specifically designed with parameters optimized for the first pass band: its capacitance value and Q value are carefully selected so that in the first pass band frequency range, the capacitor presents sufficiently high impedance to block spurious signals while maintaining low loss characteristics. This parameter optimization ensures that the capacitance Q value in the first pass band exceeds that of the high-frequency filter, thereby improving signal quality and reliability without sacrificing multi-mode support
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
The proposed solution effectively reduces insertion loss within the pass bands of acoustic wave filters connected to a common terminal, improving signal propagation without the need for additional components like splitting/combining devices or phase adjusting circuits, resulting in a more compact and cost-effective radio-frequency front end circuit.
Implementation Method 1
a second capacitor that is serially arranged on a connection path between the common terminal and the second filter. When the second filter is regarded as a capacitance, a Q value of the second capacitor in the first pass band is higher than a Q value of the capacitance in the first pass band
Data Source
AI summary
A multiplexer (1) includes: a filter (13L) that is arranged between a common terminal (100) and an input/output terminal (130) and that has a first pass band; a filter (12H) that is arranged between the common terminal (100) and an input/output terminal (120), that is formed of at least one acoustic wave resonator, and that has a second pass band located at a higher frequency than the first pass band; and a capacitor (C2) that is serially arranged on a connection path between the common terminal (100) and the filter (12H). When the filter (12H) is regarded as a capacitance, the Q value of the capacitor (C2) in the first pass band is higher than the Q value of the capacitance in the first pass band.