Common Mode Trap for Differential Duplexer Isolation
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Solution Overview
Problem
Wireless communication devices with duplexers often suffer from poor isolation between transmit and receive ports, leading to significant coupling of transmit signals to the receiver, which degrades performance and can cause receiver failure, especially due to the presence of common mode signal components.
Innovation Solution
A common mode trap is implemented in the impedance matching network of the duplexer, using series LC circuits to attenuate common mode signal components at the receive ports, with resonant frequencies set within the transmit signal range to effectively reduce transmit signal coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a duplexer is used to route RF signals between transmitter and receiver, then signal routing functionality is provided, but isolation between transmit and receive ports is poor causing transmit signal coupling to degrade receiver performance
Solution Approach 1:
The patent extracts and removes the harmful common mode signal components from the receive path by introducing a common mode trap. This trap specifically targets and eliminates the coupled transmit signals that would otherwise degrade receiver performance, separating the harmful common mode components from the useful differential mode receive signals.
Solution Approach 2:
The common mode trap acts as an intermediary element inserted into the receive signal path. It selectively interacts with common mode signals to attenuate them while leaving differential mode signals unaffected, thereby mediating between the coupled transmit signals and the receiver to protect the receiver without blocking the desired receive signals.
2Reliability
If isolation between transmit and receive ports is improved to reduce signal coupling, then receiver performance is enhanced, but device complexity increases due to additional filtering components
Solution Approach 1:
The patent applies local quality by making the impedance matching network differential while introducing a common mode trap that specifically targets common mode signals. This creates asymmetric handling of signal modes - differential mode signals pass through unaffected while common mode signals are selectively attenuated, achieving improved isolation without requiring complete redesign of the entire duplexer structure.
3Manufacturing precision
If common mode signal attenuation is increased to meet linearity requirements, then receiver specifications are met, but impact on differential mode signal handling must be minimized
Solution Approach 1:
The patent segments the signal handling into two independent pathways by using a differential impedance matching network combined with a common mode trap. This segmentation allows differential mode signals to be handled with high fidelity while common mode signals are separately targeted and attenuated, enabling independent optimization of both signal types without mutual interference.
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 common mode trap significantly attenuates common mode transmit signal components, improving receiver performance by reducing signal leakage and meeting stringent linearity requirements, while maintaining minimal impact on differential mode signal handling.
Implementation Method 1
The resonant frequencies of the series LC circuits may be set within a frequency range for the transmit signal in order to provide good attenuation of the common mode transmit signal components
Implementation Method 2
a common mode trap includes a first inductor coupled between the first node and a common node, a second inductor coupled between the second node and the common node, and a capacitor coupled between the common node and circuit ground
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
Techniques for attenuating undesired signal components from a differential duplexer are described. The duplexer provides a differential received signal at RX+ and RX- ports. This differential received signal includes an undesired common mode signal, which may come from a transmit signal. The common mode signal is attenuated with a common mode trap in an impedance matching network coupled to the RX+ and RX- ports. The matching network includes a first passive circuit coupled between the RX+ port and a first node, a second passive circuit coupled between the RX- port and a second node, and the common mode trap coupled between the first and second nodes. In one design, the common mode trap includes a first inductor coupled between the first node and a common node, a second inductor coupled between the second node and the common node, and a capacitor coupled between the common node and circuit ground.