CMOS TX/RX RF Switch Biasing for Low Loss and Isolation
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Solution Overview
Problem
Conventional CMOS single port double throw (SPDT) transmit receive radio frequency switches suffer from additional losses and non-linear distortions in the reception and transmission paths due to shunt transistors, which compromise the linearity and isolation between transmission and reception ports.
Innovation Solution
The design incorporates a combination of transistors with bulk-source connections for transmission transistors and bulk-ground connections for reception transistors using high-impedance resistors, along with virtual grounding and common biasing, to reduce PN junction effects and prevent RF leakage, thereby enhancing linearity and isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shunt transistors are used to improve isolation between transmission and reception ports, then isolation is improved, but insertion loss increases and linearity deteriorates
Solution Approach 1:
The patent removes shunt transistors from the conventional SPDT switch architecture. By extracting these harmful components, the design eliminates the source of additional losses and non-linear distortions while maintaining isolation performance through alternative means such as careful transistor sizing and switching control.
Solution Approach 2:
The patent divides the switch into separate transmission path transistors and reception path transistors with distinct sizing and biasing strategies. Transmission transistors are optimized for low loss and high linearity, while reception transistors are optimized for isolation, allowing each segment to be independently optimized without the compromising effect of shunt transistors.
2Reliability
If shunt transistors are used to improve isolation between transmission and reception ports, then isolation is improved, but linearity deteriorates
Solution Approach 1:
The patent removes shunt transistors which are the primary source of non-linear distortions. By extracting these components, the design eliminates the PN junction effects and charge storage phenomena that cause non-linearity, resulting in superior linearity performance while maintaining isolation through alternative architectural approaches.
Solution Approach 2:
The patent applies different design qualities to different parts of the switch: transmission transistors are designed with larger sizes and optimized biasing for high linearity, while reception transistors are designed for isolation performance. This local optimization allows each part to excel at its specific function without the compromising non-linear effects of shunt transistors.
Data Source
AI summary
A TX/RX RF switch that may include a reception path; and a transmission path that has an antenna port, a transmission input port, and transmission transistors. The transmission transistors have source-bulk connections. The reception path has an antenna port, a reception output port, and reception transistors. The reception path includes a first reception transistor that is closest to the antenna port, out of the reception transistors, and has a source-bulk connection, and at least one other reception transistor that has a bulk-to-ground connection. The reception transistors and the transmission transistors are CMOS transistors.