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1. LPVLSI
Module V: Low-Voltage Low-Power Memories
 Basics of SRAM, Memory Cell, Precharge
and Equalization Circuit
 Low-Power SRAM Technologies
 Basics of DRAM
 Self-Refresh Circuit
 Future Trend and Development of
DRAM.

2. LOW-POWER CMOS RANDOM ACCESS
MEMORY CIRCUITS

3. Basics of SRAMs
In general the pins of a SRAM are:
1.Addresses (Ao ... An); which define the memory location;
2. Write Enable (WE); which selects between the read and
write modes;
3. Chip Select (CS); which selects one memory out of several
within a system;
4. Output Enable (DE); which is used to enable the output
buffer; and
5. Input/Output data (I/O).
6. Power supply pins.

4. Typical SRAM architecture

5. The memory array contains the memory cells
which are readable and writable.
The row decoder (X-decoder) selects I out of
n = 2K rows, while the column decoder (Y-
decoder) selects I = 2i out of m = 2j columns.
The address (row and column) are not
multiplexed as in the case of a DRAM.
Sense amplifiers detect small voltage
variations on the memory complementary
bit-line which reduces the reading time.

6. The conditioning circuit permits the
precharge of the bit-lines.
The access time is determined by the critical
path from the address input to the data
output as shown below.
This path contains address input buffer, row
decoder, memory cell array, sense amplifier
and output buffer circuits.
The word-line decoding and bit-lines sensing
delay times are critical delay components.

7. To reduce the sensing time during a read
operation, the swing on the bit-lines should
be as small as possible.

8. The critical path for read access in SRAM

9. Typical timing of a SRAM:
(a) read cycle
(b) write cycle

10. A timing diagram during read cycle is shown above.
 During this time the data stored in a specific
SRAM location (defined by the address) is read
out.
 For a read cycle, two times are shown in the
figure; the read cycle time, tRC, and the address
access time, tAA.
 Figure shows the write cycle which permits
change to the data in an SRAM.
 Two times are indicated, the write cycle time, tWC,
and the write recovery time, tWR.

11. (Word line)
(Bit line) (Bit line bar)
6T SRAM Cell
General diagram of 6T SRAM cell

12. READ operation:

13. READ operation:

14. Write operation:

15. Source: https://www.ques10.com/p/23593/explain-read-and-write-operation-of-6-t-sram-cell-/
Write operation: