CMOS T/R Switch Shunt-Series Architecture for 60 GHz Isolation
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Solution Overview
Problem
Designing a high-isolation, low-insertion-loss transmit/receive (T/R) switch for millimeter-wave frequencies is challenging due to CMOS technology's process variability, lower carrier mobility, and increased signal coupling through the silicon substrate, making it difficult to achieve efficient power handling and isolation at 60 GHz.
Innovation Solution
A CMOS monolithic T/R switch using a shunt-series single-pole double-throw (SPDT) architecture with impedance matching networks and shunt transistors to selectively ground RF ports, optimizing transistor sizing and biasing to balance insertion loss, isolation, and power handling capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a T/R switch is implemented in CMOS technology to reduce cost and improve integration, then manufacturing cost and integrability are improved, but isolation performance deteriorates due to process variability and substrate coupling
Solution Approach 1:
The T/R switch is segmented into separate transmit and receive signal paths with independent control mechanisms. The transmit path includes a transmit switch and the receive path includes a receive switch, allowing independent optimization of each path for its specific function while maintaining high isolation between them.
Solution Approach 2:
A receive signal leakage cancellation mechanism is introduced as an intermediary component that actively compensates for leakage signals. This mechanism detects and cancels transmit signal leakage that couples through the CMOS substrate, thereby maintaining high isolation performance despite the inherent substrate coupling in CMOS technology.
2Reliability
If high isolation is achieved in a CMOS T/R switch, then receiver saturation is prevented, but insertion loss increases due to the lossy nature of CMOS at millimeter-wave frequencies
Solution Approach 1:
The operating parameters of the transistors are optimized to balance isolation and insertion loss. Transistor sizing, biasing conditions, and gate voltages are carefully selected to achieve the required isolation performance while minimizing the impact on signal transmission efficiency.
Solution Approach 2:
The T/R switch employs dynamic switching control where the transmit and receive switches are activated in complementary fashion. During transmit mode, the transmit switch is closed and receive switch is open, and vice versa during receive mode. This dynamic operation ensures high isolation when switching between modes while minimizing insertion loss during active signal transmission.
3Area of stationary object
If a single antenna is shared between transmitter and receiver using a T/R switch, then antenna quantity and system size are reduced, but signal leakage from transmitter to receiver increases
Solution Approach 1:
The receive switch is designed with preliminary protective measures to block transmit signal leakage before it can reach the receiver. The receive switch maintains a high-impedance state during transmit mode, creating a preliminary barrier that prevents strong transmit signals from coupling into the sensitive receive circuitry through the shared antenna.
Solution Approach 2:
The receive signal leakage cancellation mechanism serves as an intermediary that actively counteracts signal leakage. It detects leakage signals that manage to couple through and applies an equal and opposite signal to cancel the leakage, thereby protecting the receiver from saturation while maintaining the benefit of antenna sharing.
Data Source
AI summary
A CMOS monolithic transmit/receive switch comprises a single pole double throw switch (SPDT) module operable to selectively connect an antenna port to either a transmit port or to a receive port. A transmit matching network comprising a first transmission line matches the impedance of the transmit port of the SPDT module to a transmit impedance, and a first shunt transistor is operable to selectively ground a transmitter end of the first transmission line. A receive matching network comprising a second transmission line matches the impedance of the receive port of the SPDT module to a receive impedance, and a second shunt transistor is operable to selectively ground a receiver end of the second transmission line.