100-W Cryogenic HEMT LNAs for Quantum Computing

Low-power cryogenic LNAs are of interest in future large-scale quantum computing where available cooling capability limits the number of active circuits. We present a comparison of small-signal noise models between two different 100-nm gate-length InP HEMTs at 4 K. The HEMTs were tested in the first stage of a three-stage hybrid cryogenic 4-6 GHz LNA operating at 100-mu W dc power. The better performing cryogenic LNA exhibited 23.2 dB average gain, 2.0 K average noise temperature, and -55 dBm input 1-dB compression point. The enhanced LNA performance was attributed to the improved transconductance of the first-stage HEMT. To the authors' knowledge, this is the lowest noise reported to date for a 100-mu W transistor-based LNA aimed for qubit readout.