QBPA RF Front End With Feed-Forward Leakage Cancellation
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Solution Overview
Problem
Current RF front ends for wireless communications, particularly in full duplex (FD) and half duplex (HD) transceivers, face challenges such as high insertion loss, limited isolation, and complexity due to the use of circulators and T/R switches, which are not suitable for wide-band signals and antenna reflections.
Innovation Solution
A dual mode RF front end utilizing a quadrature balanced power amplifier (QBPA) with equal transmit paths and a feed-forward cancellation signal injected into a previously unused port, which cancels leakage signals and reflections, eliminating the need for circulators and T/R switches, and enabling low complexity and wide-band operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a circulator is used for T/R isolation in FD transceiver, then transmit and receive can occur simultaneously, but the isolation is limited and cannot ensure sufficient LNA protection
Solution Approach 1:
The patent segments the T/R isolation function into multiple stages: a first isolation stage using a T/R switch and a second isolation stage using a circulator. This segmentation allows each stage to handle specific portions of the isolation requirement, with the T/R switch providing initial isolation and the circulator providing additional isolation to achieve sufficient LNA protection while managing overall system complexity.
Solution Approach 2:
The patent introduces a T/R switch as an intermediary component between the power amplifier and the circulator. This intermediary provides initial T/R isolation and protects the circulator from full transmit power, allowing the circulator to focus on providing additional isolation without being overwhelmed by the full power signal.
2Loss of energy
If a T/R switch is used for T/R isolation in HD transceiver, then transmit and receive are separated in time, but the switch must withstand full transmit power causing high insertion loss
Solution Approach 1:
The patent segments the power handling function by introducing an intermediate amplification stage between the T/R switch and the final power amplifier. This allows the T/R switch to operate at lower power levels during receive mode, reducing insertion loss, while the intermediate and final amplification stages handle the full transmit power when needed.
Solution Approach 2:
The patent employs dynamic power amplification stages that can be activated or deactivated based on transmit/receive mode. During receive mode, the amplification stages are deactivated or operate at low gain, allowing the T/R switch to handle signals with minimal loss. During transmit mode, the amplification stages are activated to provide the necessary power amplification.
3Reliability
If additional isolation stages are added to improve LNA protection, then T/R isolation improves, but insertion loss on TX and RX paths increases
Solution Approach 1:
The patent applies different isolation mechanisms at different locations in the signal path: a T/R switch is placed close to the power amplifier to handle high-power isolation requirements, while a circulator is placed closer to the LNA to provide additional isolation for the sensitive receive path. This localized application of isolation techniques optimizes the balance between isolation performance and insertion loss.
Data Source
AI summary
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 is based on a quadrature balanced power amplifier (QBPA). The RF front end includes 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, the QBPA 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 coupled to the antenna port.