CMOS Transmit Receive Switch Transformer Reuse
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Solution Overview
Problem
Designing a CMOS transmit/receive (T/R) switch with low insertion loss, high linearity, and high isolation at GHz frequencies is challenging, especially in achieving good transmitter efficiency and receiver noise figure while maintaining isolation between transmitter and receiver.
Innovation Solution
A CMOS T/R switch architecture that reuses the PA transformer as part of the low noise amplifier (LNA) input matching network, improving insertion loss in TX mode and saving chip area while maintaining isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a CMOS T/R switch is designed to achieve low insertion loss and high linearity, then transmitter efficiency is improved, but isolation between TX and RX deteriorates
Solution Approach 1:
The T/R switch is segmented into separate TX and RX signal paths with independent switching mechanisms. The TX path uses a shunt switch configuration while the RX path uses a series switch configuration, allowing each path to be optimized independently for its specific performance requirements without compromising the other path's performance
Solution Approach 2:
An intermediate switching network is introduced between the TX and RX paths that provides galvanic isolation and impedance transformation. This intermediary structure enables low insertion loss in the TX path while maintaining high isolation to protect the RX path, resolving the contradiction between these two performance metrics
2Reliability
If a CMOS T/R switch is designed to achieve high isolation between TX and RX, then receiver protection is improved, but transmitter efficiency deteriorates
Solution Approach 1:
Different switching topologies are applied to different parts of the circuit: shunt switches with specific capacitance values are used in the TX path to minimize insertion loss, while series switches are used in the RX path to maximize isolation. Each component is locally optimized for its specific function rather than using a uniform approach throughout
Solution Approach 2:
The switch configuration is made dynamic through CMOS transistor control, allowing the circuit to switch between TX and RX modes with optimized characteristics for each mode. The switching action dynamically reconfigures the impedance and connection topology to achieve high transmitter efficiency during TX mode while maintaining high isolation during mode transitions
3Reliability
If external T/R switch components are used, then performance is improved, but bill of material cost and chip area increase
Solution Approach 1:
The T/R switch functionality is merged with the existing LNA input matching network by integrating the switching transistors directly into the matching circuit topology. This combination eliminates the need for separate external T/R switch components while maintaining the performance benefits, thereby reducing both BOM cost and chip area
Solution Approach 2:
The LNA input matching network is designed to serve dual functions: impedance matching for the receiver and T/R switching for both TX and RX paths. This multi-functional design eliminates redundant components and integrates the T/R switch functionality into the existing circuit architecture, reducing overall chip area while maintaining performance
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
The solution enhances transmitter efficiency, reduces noise figure, and conserves chip area by effectively integrating the transformer into the LNA input matching network, addressing the limitations of existing CMOS T/R switches.
Implementation Method 1
a transformer that includes a primary winding and a secondary winding
Data Source
AI summary
A transmit/receive switch architecture is provided which reuses a power amplifier's transformer as part of the low noise amplifier (LNA) input matching network. A front-end circuit includes a transmit/receive switch. The transmit/receive switch includes a transformer that includes primary winding and secondary winding. The transmit/receive also includes a transistor, where a drain of the transistor is connected to the secondary winding and a gate of the transistor is configured to receive a control signal. The transmit/receive switch operates as a receive switch when the control signal is low and inputs of the primary winding are either shorted or at open circuit. The transmit/receive switch operates as a transmit switch when the control signal is high.