Shift registers and correlators using a two-phase single-flux quantum pulse clock

A two-phase clocking scheme for rapid single flux quantum logic circuits, in particular, shift registers and correlators, is discussed. The two-phase pulse clock is generated on chip with one external clock line. The use of a two-phase clock improves the clock operating margins and eliminate the racethrough problem. A 32-b shift register has been built and tested up to a clock frequency of 21.6 GHz. A one-bit digital correlator with 32 stages has also been tested at low speed. The chips are fabricated using a Nb process.<>