Feed-Forward Canceller Tuning for Antenna Impedance Changes
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Solution Overview
Problem
Conventional methods for isolating transmit and receive signals in communication systems, such as those using RF filters and duplexers, often fail to provide sufficient isolation, especially in systems with changing antenna impedances, leading to signal leakage that degrades receiver sensitivity and introduces noise.
Innovation Solution
A method for tuning feed-forward cancellers that adjusts variable attenuators and phase-shifters based on changes in the reflection coefficient, using a lookup table to correct for non-ideal effects, to maintain effective signal cancellation across dynamic environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional RF filters and duplexers are used for signal isolation, then the system structure is simple, but the isolation between transmit and receive signals is insufficient
Solution Approach 1:
The patent introduces a feed-forward canceller as an intermediary component between the transmit and receive paths. This canceller includes a subtractor that subtracts a canceled signal (generated by scaling and phase-shifting the transmit signal) from the receive signal, thereby actively removing transmit signal leakage from the receive path and improving isolation beyond what passive filters and duplexers can achieve
Solution Approach 2:
The patent employs variable attenuators and variable phase shifters within the feed-forward canceller to dynamically adjust the amplitude and phase of the canceled signal. These parameter changes allow the system to adapt to varying antenna impedances and environmental conditions, maintaining effective signal cancellation and isolation despite changes in the electromagnetic environment
2Stability of the object's composition
If fixed isolation methods are used, then the system is stable, but the isolation degrades when antenna impedance changes
Solution Approach 1:
The patent implements a feedback mechanism where the system continuously monitors the receive signal for residual transmit leakage and adjusts the variable attenuators and phase shifters accordingly. This feedback loop enables the system to maintain stable isolation levels by dynamically compensating for antenna impedance changes and environmental variations, ensuring consistent performance across different operating conditions
Solution Approach 2:
The patent transitions from static isolation components to dynamic adjustable components within the feed-forward canceller. The variable attenuators and phase shifters can be tuned in real-time to match changing antenna impedance conditions, providing both stability through active maintenance of isolation levels and adaptability to varying environmental conditions
3Object-generated harmful factors
If feed-forward canceller is added to improve isolation, then signal leakage is reduced, but the device complexity increases
Solution Approach 1:
The patent segments the signal processing function into distinct components: the main receive path, the transmit signal sampling path, the signal conditioning path with variable attenuators and phase shifters, and the subtraction path. This segmentation allows each component to perform its specific function efficiently, making the overall complex system more manageable and maintainable while achieving superior isolation performance
Solution Approach 2:
The patent creates a copy of the transmit signal through a coupler and processes this copied signal through variable attenuators and phase shifters to generate the canceled signal. This copying approach allows the system to generate an accurate replica of the transmit leakage for cancellation purposes without interfering with the main transmit path, achieving effective leakage reduction while maintaining system simplicity
Data Source
AI summary
A method for maintaining good cancelation in a passive feed-forward cancelation circuit is disclosed. The feed-forward cancelation circuit may include at least one path which may comprise a phase-shifter and a variable attenuator. This method uses the complex value of the reflection coefficient at the point where the communication device is connected to a transmission medium, such as an antenna, to determine the values for the phase shifter(s) and the variable attenuator(s).