A Josephson junction to FET high speed line driver made of TlCaBaCuO

We have used a Tl-Ca-Ba-Cu-O superconducting flux flow transistor (SFFT) as an active impedance converter between Josephson and FET circuitry. The input of the flux flow device is a control line of low impedance that can be driven by a tunnel junction. The output is the signal across the SFFT which is made of a parallel array of weak links. The output impedance is typically greater than 5 Ohm with a maximum voltage swing of over 100 mV into a 50 Ohm system. The switching of an all-Nb junction induced a 90 mV voltage swing at the FET input and over 200 mV at the FET output. The line driver can operate anywhere between 4.2 and 85 K with minor changes in speed (plus or minus 5 ps) and output level (plus or minus 10 mV). The switching time measured was about 100 ps and was fixture limited.