Investigation of Robust CMOS Amplifiers for Josephson-CMOS Hybrid Memories

In this paper, we investigated three types of robust and high-speed cryogenic CMOS amplifiers for Josephson-CMOS hybrid memories. One is a cascaded CMOS amplifier and the others are source-follower CMOS amplifiers. The source-follower CMOS amplifiers consist of a first-stage PMOS-input source-follower to shift the input voltage level, and a second-stage self-biased differential amplifier. For the first-stage source-follower, we employed two types of circuits: a single-ended source-follower and a self-biased differential source-follower. We compared their performance and robustness by circuit simulations using a cryogenic device model. It was found that the amplifier with the self-biased differential source-follower has better characteristics in terms of speed, power consumption and robustness. We also measured transient characteristics of the amplifiers at liquid helium temperature and showed that the amplifier with the self-biased differential source-follower has wider and robust bias margins.