Transcript Memory
Memory ETEG 431 SG Semiconductor Memory Classification • Size: Bits, Bytes, Words. • Timing Parameter: • Function: Read, Write Cycle… ROM, RWM, Volatile, Static, … • Access Pattern: RAM, FIFO, LIFO,… • Input/Output Architecture: • Application: Multiport… Embedded, Secondary, … Memory ETEG 431 SG Semiconductor Memory Classification Read-Write Memory Non-Volatile Read-Write Read-Only Memory Memory Random Access Non-Random Access EPROM 2 E PROM SRAM FIFO DRAM LIFO Shift Register CAM Mask-Programmed FLASH Programmable (PROM) Memory ETEG 431 SG Memory Architectures M bits S0 Word 0 S1 Word 1 S2 Word 2 words N SN 2 2 SN 2 1 Word N 2 2 Word N 2 1 Input-Output (M bits) Storage cell • N-word memory • M-bits • Select bits (So-SN-1) • Good for Small Memories • Not for Large ones • Too many Select Signals Memory ETEG 431 SG Memory Architectures: Decoder M bits S0 A0 Word 1 A1 Word 2 A K2 1 • K address bits Word 0 DecoderWord N- 2 Word N - 1 K = log2N Input-Output (M bits) Storage cell • N = 2K • Decoder reduces the number of select signals Memory ETEG 431 SG Memory Architectures: Decoder (Contd.) • Reduces the number of external address lines. • Memory Aspect Ratio??? • Shape of storage cell is approximately square. • Excessively long vertical wires. Memory ETEG 431 SG Memory Architectures: Array ll • Aspect ratio approaches Unity • Logic swing, noise margin, fanout, … Amplify swing to rail-to-rail amplitude Selects appropriate word Memory ETEG 431 SG Hierarchical Memory Architecture Memory ETEG 431 SG Hierarchical Memory Architecture (Contd..) • Larger Memories: Slower. • Add one extra dimension. • Block address. • Shorter wires within blocks. • Power Saving: Block address activates only one block. Memory ETEG 431 SG CMOS SRAM Cell WL V DD M2 M5 Q M1 BL M4 Q M6 M3 BL 6 Transistor CMOS SRAM Cell Memory ETEG 431 SG CMOS SRAM: Read Operation • Pre-charge bit lines to … VDD/2. • Assert the word line. • Read Upset. • Small sized cell: Very slow discharge. • Sense Amplifier. Memory ETEG 431 SG CMOS SRAM: Write Operation • NMOS: Strong 0. • Pull voltage below the threshold value. Memory ETEG 431 SG 1-T DRAM