Ultra-low noise and low power 18.7 GHz radiometer LNAs in a 0.5 THz SiGe technology utilizing back-side etched inductors

This paper presents two 18.7 GHz low-noise amplifiers (LNAs) for radiometer applications designed in a SiGe technology featuring HBTs with peak fT / fMAX of 300/500 GHz. Back-side substrate etching is utilized to reduce inductor losses and improves the noise figure (NF) of the LNAs by an average of 0.12 dB across the measured band. At 18.7 GHz, the first LNA achieves 1.10 dB NF, 17.1 dBm OIP₃, and 8.6 dB gain while consuming only 5 mW of power. The second LNA achieves 1.48 dB NF, 11.5 dBm OIP₃, and 13.9 dB gain while consuming 10 mW of power. To the authors´ best knowledge, these amplifiers have the lowest measured NF of all silicon-based LNAs at this frequency and are competitive with the best III-V LNAs.