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 com munication channel switches. The core of the circuit is a tree of the single-bit SFQ demultiplexer with toggle (rather than the reset-set) c ontrol. Three new RSFQ cells: the demultiplexer, D flip-flop with comp lementary outputs, and serial XOR with large parameter tolerances (dc bias margins of +/-25%, +/-26%; and +/-27% respectively) have been dev eloped for the decoder project. We have designed the first 16-bit prot otype of the decoder for 1-kA/cm(2) niobium-trilayer technology and te sted it at low frequencies. The circuit was completely operable except for 3 (of 16) output SFQ/DC converters. Simulations show that the cir cuit should allow data rate in excess of 60 Gbit/s and channel switchi ng time below 20 ps.