RF Front End Using Quadrature PA for TX-RX Isolation
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Solution Overview
Problem
Existing radio frequency front ends that use a single antenna for both transmitting and receiving face challenges in providing sufficient isolation between the transmit and receive paths without bulky components, limited bandwidth, and high costs, especially when integrating with Monolithic Microwave Integrated Circuits or Radio Frequency Integrated Circuits.
Innovation Solution
A radio frequency front end employing a quadrature balanced power amplifier with input and output couplers that divide and combine signals to achieve isolation between the transmit and receive paths, eliminating the need for bulky elements like circulators and allowing integration with RF ICs, while maintaining low insertion loss and adequate power handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If commercial circulators made of ferrite/magnetic materials are used to provide isolation between transmit and receive paths, then good isolation and low insertion loss are achieved, but the device becomes bulky and tall, incompatible with integration technology, and expensive
Solution Approach 1:
The patent replaces the mechanical/ferrite-based circulator with an electrical circuit implementation using transmission line transformers and switching elements. This substitution eliminates the need for bulky magnetic materials while achieving the same isolation function through electrical circuitry that can be integrated on a PCB or integrated circuit.
Solution Approach 2:
The patent combines the isolation function with the existing transmit and receive path circuitry by using the transmission line transformers and switches that are already part of the RF front-end architecture. This merging eliminates the need for a separate bulky circulator component while maintaining the isolation function.
2Ease of manufacture
If magnetic-free circulators based on 3λ/4 transmission line are used for integration, then compatibility with integration technology is achieved, but power handling capability is limited and loss is relatively high
Solution Approach 1:
The patent segments the signal path into multiple transmission line sections with specific impedance transformations. By using multiple stages of transmission line transformers rather than a single long 3λ/4 line, the design achieves better power handling while maintaining integration compatibility.
Solution Approach 2:
The patent optimizes the transmission line characteristic impedances and electrical lengths to achieve both good power handling and low loss. By carefully selecting the impedance values and physical dimensions of the transmission lines, the design overcomes the limitations of conventional magnetic-free circulators.
3Reliability
If signal switches are used to alternatingly connect antenna to transmit and receive paths in half-duplex mode, then isolation is provided, but transmitting and receiving cannot occur simultaneously
Solution Approach 1:
The patent uses dynamic switching elements that can rapidly transition between connecting the antenna to the transmit path or receive path. This dynamic switching enables full-duplex operation where both paths are simultaneously connected to the antenna, unlike static switching arrangements that require half-duplex operation.
Solution Approach 2:
The transmission line transformers act as intermediaries between the antenna and the transmit/receive paths. These transformers provide the necessary isolation and impedance matching to enable simultaneous connection of both paths to the antenna, facilitating full-duplex operation while maintaining signal integrity.
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
This solution provides significant isolation between the transmit and receive paths with minimal loss, enabling efficient wireless communication without bulky components, supporting integration and reducing size, weight, and cost, while maintaining low insertion loss and wide bandwidth compatibility.
Implementation Method 1
A radio frequency front end employs a quadrature balanced power amplifier with input and output couplers that divide and combine signals to achieve isolation between the transmit and receive paths
Data Source
Figure 1a~1c
Figure 2
AI summary
The present invention relates to a radio frequency front end for wireless communication, es- pecially to a radio frequency front end (100) in which transmitting and receiving is performed using the same antenna. The front end comprises an antenna port (111) adapted to connect the antenna (110), a receive path (140) comprising a receive signal input (141) adapted to receive a receive signal (150), and a transmit path (120) adapted to supply a transmit signal (130) to the antenna port (111), the transmit path (120) comprising a quadrature balanced power amplifier (160) having a transmit signal output port (163) connected to the antenna port (111) and an output isolated port (164) connected to the receive signal input (141).