I'm a beginner trying to understand the working of SRAM and DRAM.

According to sources, DRAMs use a single transistor along with a capacitor(1T1C) to store a single bit, where the capacitor holds the charge that denotes the state (1 or 0) of the particular memory cell(and of-course the capacitor needs to be refreshed periodically to overcome leakage).

Now in case of an SRAM, how does a flip-flop(assuming transistor only circuit) retain its state (1 or 0) after the input signal is cut-off?

Please correct me if my understanding of DRAM/SRAM is wrong.

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    \$\begingroup\$ Flipflop is a bi-stable circuit. \$\endgroup\$ – Eugene Sh. Dec 20 '17 at 15:35
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    \$\begingroup\$ "..how does a flip-flop in an SRAM.." An SRAM does not use FFs for storing data. It uses six CMOS gates. Look up SRAM on WIKI! \$\endgroup\$ – Oldfart Dec 20 '17 at 15:38
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    \$\begingroup\$ @user3535598 And the first sentence on Wikipedia says "Static random-access memory (static RAM or SRAM) is a type of semiconductor memory that uses bistable latching circuitry (flip-flop) to store each bit" \$\endgroup\$ – Finbarr Dec 20 '17 at 15:42
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    \$\begingroup\$ I'm voting to close this question as off-topic because lack of research effort. \$\endgroup\$ – winny Dec 20 '17 at 17:03
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    \$\begingroup\$ @winny I don't believe that's actually a reason to close a question here. The goal of stack exchange is to become the repository of all great info. Regardless of how basic a question is, I believe stack exchange would love to be the first google hit. \$\endgroup\$ – horta Dec 20 '17 at 18:02

It's two inverters that use positive feedback to retain a bit. Once the bit is setup and there remains power, the two inverters will forever be stuck in that same state. To change the bit, you have to override the internal positive feedback of the system. You would do that through M5 and M6. enter image description here


An SRAM cell is actually two crossed feedback loops. Look at its schematic and you will immediately see it. As long as the SRAM has power, the loops are running and maintain their state, even without any input signal.


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