A resonant switch for LNA protection in watt-level CMOS transceivers

An integrated resonant switch designed to protect low-noise amplifier (LNA) circuits in CMOS transceivers is reported. The design implements the receive-path portion of a transmit/receive switch protecting 3-V-process transistors from 5 W (22-V peak) transmit signals while simultaneously helping to achieve a good LNA noise figure on receive and low power loss on transmit. Since the approach is to combine an LNA´s matching network and switch functions, the design has no traditional insertion loss on receive. The effective loss to the transmitted signal is less than 0.5 dB using moderate quality inductors (Q>6) and 0.1 dB using Q=12 inductors achievable in most RF-aware CMOS silicon-on-insulator foundries at UHF through S-band frequencies.