QBPA RF Front End With Feed-Forward Cancellation for T/R Isolation
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Solution Overview
Problem
Existing RF front ends for wireless communication systems face challenges in achieving high isolation, low insertion loss, and wide-bandwidth performance, particularly in the presence of transmit antenna reflections, and there is a lack of dual mode RF front ends suitable for both full and half duplex operations.
Innovation Solution
A dual mode RF front end utilizing a Quadrature Balanced Power Amplifier (QBPA) with equal signal paths and a feed-forward cancellation signal to cancel transmit signal reflections, eliminating the need for circulators and switches, and ensuring high T/R isolation and wide-band capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a circulator is used for T/R isolation in FD mode, then isolation is improved, but device complexity, size, and cost increase
Solution Approach 1:
The patent extracts and eliminates the circulator component from the RF front end design. Instead of using a circulator for T/R isolation, the invention employs a T/R switch combined with a feed-forward cancellation network that cancels transmit signal leakage and antenna reflections through destructive interference, thereby achieving high isolation without the bulky and expensive circulator
Solution Approach 2:
The patent introduces a feed-forward cancellation network as an intermediary mechanism. This network includes a cancellation signal generator and combiner that create an inverted copy of the transmit signal to cancel out leakage and reflections at the receive port, serving as a mediator to achieve isolation without direct component isolation
2Device complexity
If a T/R switch is used for HD mode, then device complexity is reduced, but insertion loss increases with frequency
Solution Approach 1:
The patent designs a dual-mode RF front end that can operate in both HD and FD modes using the same T/R switch architecture. The switch is configured to provide isolation in HD mode and works in conjunction with the feed-forward cancellation network to provide isolation in FD mode, making the system universal for both operating modes while maintaining low insertion loss
Solution Approach 2:
The patent optimizes the T/R switch parameters and the feed-forward cancellation network parameters to minimize insertion loss across the operating frequency band. By adjusting the cancellation network coefficients and switch timing, the system achieves low loss performance that varies optimally with frequency
3Reliability
If SIC filter is added for FD operation, then T/R isolation is improved, but device complexity and signal loss increase
Solution Approach 1:
The patent merges the isolation function and the cancellation function into a single integrated feed-forward network. Instead of adding a separate SIC filter stage, the cancellation signal generation and combination is integrated with the T/R switch architecture, achieving both isolation and cancellation in one unified structure that reduces overall device complexity
Data Source
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AI summary
The present relates to a Radio Frequency (RF) front end for wireless communications, in particular for use in a Half Duplex (HD) and/or Full Duplex (FD) transceiver. The RF front end of the invention is especially based on a Quadrature Balanced Power Amplifier (QBPA). The RF front end comprises an antenna port for outputting a transmit signal to and receiving a receive signal from an antenna, and a receive port for outputting the receive signal to a signal processing section. Further, it comprises the QBPA, which is configured to: receive a transmit input signal at a first port, receive a cancellation input signal at a fourth port, and receive the receive signal at a second port connected to the antenna port. Further, the QBPA is configured to generate the transmit signal from the transmit input signal and output the transmit signal at the second port, and generate a cancellation signal from the cancellation input signal and output the cancellation signal and the receive signal at a third port connected to the receive port.