A Josephson 10-b instruction 128-word ROM unit

A Josephson instruction read-only memory unit (IROU) has been demonstrated. The IROU, which is composed of a 10-b*128-word ROM plane, a 6-64 decoder, two multiplexers, and several buffers, stores a program for the Josephson computer ETL-JC1. The ROM plane was designed using two-junction DC-SQUID-type ROM cells, in which the zero ROM cell has no junction and no superconducting loop and one ROM cell has a damping resistor. The peripheral circuits were designed using a 4JL family of OR, AND, INVERT, and AMP gates. The IROU chip was fabricated using a Nb-AlO/sub x/-Nb Josephson tunnel junction IC technology with a 3- mu m design rule. There were 1280 ROM cells and 789 4JL gates integrated on the 5-mm*3.45-mm chip. All 128 words of the ROM plane could be read with a total power dissipation of 1.63 mW. The minimum total access time was measured to be 390 ps.>