DRAM cell operation

What is DRAM?

   Dynamic random-access memory (DRAM) is a type of random-access memory that stores each bit of data in a separate capacitor within an integrated circuit. The capacitor can be either charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1. Since capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically. Because of this refresh requirement, it is a dynamic memory as opposed to SRAM and other static memory.

Operation :

  •Write:

–1. Drive bit line

–2. Select row

•Read:

–1. Precharge bit line to Vdd/2

–2. Select row

–3. Cell and bit line share charges

»Minute voltage changes on the bit line

–4. Sense (fancy sense amp)

»Can detect changes of ~1 million electrons

–5. Write: restore the value

•Refresh

–1. Just do a dummy read to every cell.

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