Cryogenic Characterization of RF Low-Noise Amplifiers Utilizing Inverse-Mode SiGe HBTs for Extreme Environment Applications

The cryogenic performance of radiation-hardened radio-frequency (RF) low-noise amplifiers (LNAs) is presented. The LNA, which was originally proposed for the mitigation of single-event transients (SETs) in a radiation environment, uses inverse-mode silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) in its core cascode stages. In this prototype, the upper common-base SiGe HBT is configured in inverse mode for balanced RF performance and reduced SET sensitivity. In order to better exploit the inverse-mode LNAs in a variety of extreme-environment applications, the RF performance of the LNA was characterized using liquid nitrogen to evaluate cryogenic operation down to 78 K. While the SiGe LNA exhibits acceptable RF performance for all temperature conditions, there is a noticeable gain drop observed at 78 K compared to the conventional forward-mode design. This is attributed to the limited high-frequency performance of an inverse-mode SiGe HBT. As a guideline, compensation techniques, including layout modifications and profile optimization, are discussed for the mitigation of the observed gain degradation.