High-Speed Operation of Random-Access-Memory-Embedded Microprocessor With Minimal Instruction Set Architecture Based on Rapid Single-Flux-Quantum Logic

We present design and experimental results of a rapid single-flux-quantum (RSFQ) bit-serial microprocessor with reduced-size embedded random access memories (RAMs) and with a minimal instruction set, called CORE e2h. The microprocessors called CORE e series have been developed for demonstrating small-scale program execution, such as loop calculation and sorting, in order to show the first prototype of a stored-program computer using the RSFQ technology. The CORE e2h is the most simplified variation of the CORE e series, which is equipped with only two registers, and can execute 13 instructions. The target clock frequency for bit-serial operation is 50 GHz, while the designed system clock cycle is 2 GHz. We carefully designed every component, implementing functionality using a small number of Josephson junctions with a small footprint. We fabricated several chips of the CORE e2h microprocessor integrated with two 128-bit shift-register-based RAMs on the same die. We experimentally obtained correct operations for all the instructions, and confirmed high-speed transfer between the instruction memory and controller unit and between the data memory and datapath at around 50 GHz.