Elimination of the feed-through effect in vortex flow transistors

The capacitive feed-through effect in a VFT (vortex flow transistor) has been identified as a major limiting factor for high-frequency distributed amplifier applications. Two techniques to eliminate this effect are proposed and discussed. They are the use of a balanced controlled VFT and the use of a modified super current injection transistor. The balanced controlled configuration consists of a pair of Josephson junctions driven by control lines excited by push-pull. The simulations show more than 100-dB improvement in S12 over a single-ended device up to 175 GHz. The modified superconducting current injection transistor is a current controlled current source allowing the output line to be fed against ground. Hence, capacitive feed-through effects are greatly reduced. Device layouts and fabrication techniques are discussed.