Page: Module 4 : Unit 2
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Semiconductor memories

SRAM DRAM
Retained stored info as long as power supply On. Content is lost as soon as supply is removed loses its stored info in a few milli sec even though its power supply is on
Uses conventional flip Flop to store bit 0 or 1 store info in the form of charge on a cap
6 transistor to form A mem cell Low packing density 1 transistor per mem cell high packing density
Faster cheaper

6T SRAM

=> write 1

• Make WL= 1

• M3 and M4 =on

• Force data line to “1” and data to “0”

• VQ=0 M1÷off and VQ

• 1 is written (Vq=1)

=> write ‘0’ opreation

• Force data =0 and data=’1’

=> VQ=0 M2=off and VQ M1 om

=> VQ=0 and VQ=1

• Data and data precharged to Vcc

• WL is activated

• M3 and M4 =on

• Vq=1 and Vq=0 i.e. M2= on and M1- off

• Vq > Vq is read as logic 1

• Vq=0 and Vq=1 i.e. M2-off and M1-on

• Vq<Vq is read as logic ‘0’</p>

IT DRAM

• Prior to lead ops DL is precharged to Vdd/2 now WL is activated

• If DRAM is storing ‘1’ i.e. the cap data is charged than this charge is shared with dataline capacitor

• Senseamp senses this charge and generates a valid output data.

When volt at DL increases stored bit is ‘1’ and when volt DL decreases stored bit is ‘0’

3T DRAM

=> write ‘1’ ops

• Force D=1 & D=0

• Wriwriline is activated M1- on

• C1 &C share the charges

• A &teb write aps wordline is mode ‘0’

• Precharge C1 &C2 to logic 1 level

• activate read line (R) =3 -DN

• -1 is stored M2= on

• C2 discharge (M2 & M3)

• voltage at ‘0’ decreases interpreted ad ‘1’

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