These pages describe the development of a 4 to 8 GHz cryogenic low-noise amplifier (LNA), including simulations, design, assembly, and testing. The purpose of this document is to provide detailed explanations of the project to allow others to continue the development, assembly, and testing of similar LNAs.

The Quasi-Monolithic Microwave Integrated Circuit (QMMIC) amplifier consists of a thin-film passive circuit on a GaAs substrate with three 160 micron gate InP HEMTs bump-bonded to it. The measured amplifier gain is over 32 dB and noise is approximately 8 Kelvin from 4 to 8 GHz at a physical temperature of 4 Kelvin.

This amplifier was designed for use in a 690 GHz SIS receiver operating in a liquid helium cryostat. Design goals included low noise, high gain, low power consumption, unconditional stability, and a compact housing.