| 摘要 |
PURPOSE:To provide a multi-valued read-only memory (ROM) device requiring no additional process, having excellent affinity with a CMOS process and having fast working speed. CONSTITUTION:The channel length of ROM cells is represented by four kinds of L1, L2, L3, L4 respectively in order to show the states of quaternary (00), (01), (10), (11), and transistors RTR1, RTR2, RTR3. RTR4 for specifying reference voltage formed in the same channel length as channel length for discriminating these quaternary states are mounted. That is, quaternary is discriminated by using the transistors in four kinds of channel length as a whole. Outputs from ROM cells selected in a ROM cell array 14A are compared with reference voltage REF1-REF4 by comparison circuits CMP1-CMP4, and either of quaternary is discriminated by a decoder circuit 20A. |
