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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