Gain-Frequency characteristics of transistors based on flux flow in hysteretic Long Josephson Junctions (LJJ)

Transistors based on one dimensional flux flow in hysteretic Long Josephson Junctions (LJJ) and deriving output from the spatial average over the leng th can be modeled as a section of transmission line. Time domain analyses m ade on these transmission line sections with both the ends terminated with typical resistance values reveal a fundamental gain-frequency relationship unique to all devices whose output voltage is equal to the spatial average over the length of the junction. The maximum frequency of a transistor depe nds on the transit time of carriers and the parasitic elements. The analysi s shows that the frequency response of a flux flow transistor is related bu t not equal to the inverse of the transit time of fluxons. Secondly the ste p response of these transmission line sections varies linearly with time, w hich indicates a slew rate limitation. The slew rate that affects the high frequency response of a flux flow device is shown to be a function of the c ritical current density of the junction and material parameters. Analysis m ade on niobium-lead junctions indicates that the slew rate peaks at an opti mum current density level. The results of these analyses and performance co mparisons are presented.