4-bit rapid single-flux-quantum decoder

We describe the design of a fast single-flux-quantum decoder which can be used, e.g., in fast RAMs, general-purpose microprocessors, and communication channel switches. The core of the circuit is a tree of the single-bit SFQ demultiplexer with toggle (rather than the reset-set) control. Three new RSFQ cells: the demultiplexer, D flip-flop with complementary outputs, and serial XOR with large parameter tolerances (dc bias margins of /spl plusmn/25%, /spl plusmn/26%, and /spl plusmn/27%, respectively) have been developed for the decoder project. We have designed the first 16-bit prototype of the decoder for 1-kA/cm/sup 2/ niobium-trilayer technology and tested it at low frequencies. The circuit was completely operable except for 3 (of 16) output SFQ/DC converters. Simulations show that the circuit should allow data rate in excess of 60 Gbit/s and channel switching time below 20 ps.>