Design and component test of SFQ shift register memories

The lack of a high-density and high-speed memory is a serious impediment for realization of large-scale RSFQ digital systems. A shift resister memory, which has high throughput and simple circuit structure, is one candidate to overcome this drawback. We show a design framework of the shift register memory, which is usable for the high-speed register files and the main memories of the RSFQ microprocessor. The proposed system consists of an array of shift registers and a packet decoder that switches a high-speed serial data stream into the specified shift register. The target clock frequency is 16 GHz assuming 2.5 kA/cm² Nb standard process. We have estimated the propagation delay and the circuit area of the data-driven self-timed (DDST) packet decoder. Based on this estimation, we have also evaluated the access time and the area of the memory system. Several key components, including the one-to-two packet switch and the one-to-four DDST packet decoder, were implemented and their correct operations were confirmed.