High frequency operation of JTL ring oscillator with a passive transmission line

We have designed ring oscillators to test rapid single flux quantum (RSFQ) circuits with passive transmission lines at high frequencies. To reduce the width of the transmission line, design methods for increasing the characteristic impedance of the transmission line have been investigated and then we designed a 5-stage of Josephson transmission line (JTL) receiver which can transform the impedance from 1 to 4 Ω by changing the critical current and the inductance. The receiver, driver, and micro-strip line were inserted in a ring oscillator. The ring oscillator fabricated with the Nb/AlOx/Nb junction process was successfully operated at frequencies ranging from 6 to 10 GHz for line lengths of 0.6, 3, 6, and 9 mm. The usefulness of the impedance transformation was then confirmed experimentally. A propagation delay per unit length of 8.4 ps/mm was also obtained