DRAM

Why is a boosted voltage (VPP), higher than the supply voltage, used to drive DRAM word lines?

  1. ATo make refresh unnecessary
  2. BTo avoid losing a threshold voltage across the cell transistor so the capacitor is written with a full voltage
  3. CTo lower the bit-line voltage
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Answer: B. To avoid losing a threshold voltage across the cell transistor so the capacitor is written with a full voltage

The cell transistor is an nMOS device, so if its gate were driven only to the supply voltage, the capacitor could be written only to a voltage one threshold voltage lower. Driving the word line with VPP, at least a threshold voltage above the supply, writes a full "1" voltage to the capacitor and secures read margin.

  • A. Refresh is still required even with boosting.
  • B. Correct. It avoids the threshold voltage drop.
  • C. It is not meant to lower the bit-line voltage.
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More DRAM questions

  1. Which correctly describes the structure of a typical 1-bit DRAM memory cell?
  2. Why does DRAM need periodic refresh operations?
  3. Which correctly describes the read operation of DRAM?
  4. Which pair of three-dimensional structures has been used in DRAM cells to secure capacitor capacitance?
  5. Which correctly describes a property of DRAM?