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, has a function of storing a program for the Josephson computer ETL-JCl. The ROM plane has been designed using two-junction dc-SQUID type ROM cells, in which the zero ROM cell has no junction and no superconducting loop and the one ROM cell has a damping resistor. The peripheral circuits have been designed using a 4JL family of or, AND, INVERT, and AMP gates. The IROU chip was fabricated using a Nb/AIOx./Nb Josephson tunnel junction IC technology with a 3-µm 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 the total power dissipation of 1.63 mW. The minimum total access time was measured to be 390 ps. © 1990 IEEE