High-Frequency Switch Module Isolation via Capacitive Coupling
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Solution Overview
Problem
High-frequency signal leakage occurs between closely arranged selected terminals in switch modules, degrading transmission characteristics due to harmonic interference between communication bands, and existing solutions increase the size of the switch module by requiring high inductance to achieve isolation.
Innovation Solution
A high-frequency switch module configuration with a switch element, filter element, and inductor, where transmission conductors are positioned to enhance capacitive coupling without increasing inductance, using a multilayer circuit board with overlapping conductors and a spiral-shaped inductor to maintain resonant frequency and ensure isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If selected terminals are arranged close to each other along one side of the housing, then the switch element structure is compact, but high-frequency signal leakage occurs between terminals degrading transmission characteristics
Solution Approach 1:
An inductor is introduced as an intermediary component connected between transmission lines of different selected terminals. This inductor forms a parallel resonant circuit with the capacitive coupling between terminals, creating a high-impedance barrier that blocks high-frequency signal leakage while allowing the terminals to remain closely arranged for compact structure.
Solution Approach 2:
The patent adjusts the inductance value of the added inductor to achieve parallel resonance at the problematic harmonic frequency. By changing the inductance parameter to match the resonant frequency condition (1/(2π√(LC))), the system creates maximum impedance at that frequency, effectively blocking signal leakage without requiring increased terminal separation.
2Object-generated harmful factors
If an inductor is added between transmission lines to ensure isolation between selected terminals, then signal leakage is reduced, but the inductance L must be increased which enlarges the switch module size
Solution Approach 1:
The patent optimizes the inductance value by utilizing the existing small capacitance from terminal coupling. Since resonant frequency is determined by 1/(2π√(LC)), the small C value allows for a smaller L value to achieve the same resonant frequency, thus reducing the inductor size compared to conventional designs that don't exploit this capacitive coupling effect.
Solution Approach 2:
The capacitive coupling that naturally exists between closely arranged selected terminals is not treated as a problem to be eliminated, but rather utilized as a beneficial resource. This inherent capacitance serves as one half of the resonant circuit, eliminating the need to add separate capacitors and allowing the system to achieve isolation with a smaller inductor.
3Volume of moving object
If the capacitance C from capacitive coupling between selected terminals is used, then the inductance L can be reduced, but the capacitance value is extremely low requiring precise control
Solution Approach 1:
The patent employs transmission conductors with specific geometric configurations (parallel arrangements, overlapping sections, controlled spacing) to create the capacitive coupling effect. This geometric approach to controlling capacitance is more manufacturable and stable than trying to control tiny capacitor values, as it relies on physical dimensions that are easier to control during PCB fabrication and assembly.
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 solution enables high-frequency switch modules with improved isolation and superior transmission characteristics while maintaining a small size, reducing the risk of harmonic leakage and fluctuations in capacitive coupling.
Implementation Method 1
Isolation between the first selected terminal and the second selected terminal is ensured by parallel resonance between this inductor (inductance L) and a capacitor (capacitance C) provided by capacitive coupling between the first selected terminal and the second selected terminal.
Implementation Method 2
a capacitor (capacitance C) provided by capacitive coupling between the first selected terminal and the second selected terminal
Data Source
AI summary
A high-frequency switch module includes a switch element, a filter element, an inductor, and first and second transmission conductors. The switch element includes a common terminal and first and second selected terminals selectively connected to the common terminal. The first transmission conductor connects the first selected terminal and a SAW filter of the filter element. The second transmission conductor connects the second selected terminal and a SAW filter of the filter element. The inductor is connected between the first and second transmission conductors. A separation distance between at least a portion of the first transmission conductor and a portion of the second transmission conductor is shorter than a separation distance between a land conductor of the first selected terminal and a land conductor of the second selected terminal, and the transmission conductors are capacitively coupled.