3. introduction
1. Data storage essential for processing.
2. Binary storage.
3. Switches.
4. Random & Efficient access to all memory location.
5. Data access is fast so less data access time.
6. Data accessed by means of binary memory address
applied to chip’s address pins.
'0'
'1'
Read
Write
4. Requirements
1. Easy reading.
2. Easy Writing.
3. High density.
4. Speed, more speed and still more speed.
5. Bulkier data processing.
6. Minimizing the amount of error.
5. Memory Chip
Configuration
RowDec
Memory Cell Array
Row Address
N bits
Complete Address
N+M Bits
2
M
Cells
Din
Dout
I/O Control
din
dout
Column Dec.
2
N
Cells
WL
DL
Cell
Control
Signals
I/OInterface
Column Address
M Bits
7. RAM
1. Random write and read operation for any cell
2. Volatile data
3. Most of computer memory
4. DRAM
Low Cost
High Density
Medium Speed
5. SRAM
High Speed
Ease of use
Medium Cost
8. 1-Transistor DRAM Cell
CS
M1
BL
WL
CBL
WL
X
BL
VDD VT
VDD/2
VDD
GND
Write "1" Read "1"
sensing
VDD/2
V VBL VPRE– VBIT VPRE–
CS
CS CBL+
------------------------= =
Write: CS is charged or discharged by asserting WL and BL.
Read: Charge redistribution takes places between bit line and storage capacitance
Voltage swing is small; typically around 250 mV.
10. ROM
1. Non-volatile Data
2. Method of Data Writing
3. Mask ROM
Data written during chip fabrication
4. PROM
Fuse ROM: Non-rewritable
EPROM: Erase data by UV rays
EEPROM: Erase and write through electrical means
o Speed 2-3 times slower than RAM
o Upper limit on write operations
o Flash Memory – High density, Low Cost
13. Non-Volatile Memories
The Floating-gate transistor
(FAMOS)
Floating gate
Source
Substrate
Gate
Drain
n+ n+_
p
tox
tox
Device cross-section Schematic symbol
G
S
D
14. Floating-Gate Transistor
Programming
0 V
- 5 V 0 V
DS
Removing programming
voltage leaves charge trapped
5 V
- 2.5 V 5 V
DS
Programming results in
higher VT.
20 V
10 V 5 V 20 V
DS
Avalanche injection
23. CONCLUSION
Use of microprocessor controlled items has
increased with time, so the requirement of
semi conductor memory has increased.
It is the additional driver, that has made the
software associated with computers more
sophisticated .
