SRAM and flash memory
Which is an example of a "write assist" technique to prevent SRAM write failures at low voltage?
- APulling the bit line on the 0 side slightly below ground during a write
- BRaising the cell supply voltage during a write
- CLowering the word-line voltage
Show answer and explanation
Answer: A. Pulling the bit line on the 0 side slightly below ground during a write
At low voltage, the access transistor's drive becomes insufficient to overpower the cell's pull-up, so writes tend to fail. Pulling the bit line on the side being written to 0 down to a negative voltage (negative bit line) increases the access transistor's drive and makes writing easier. Lowering the cell supply during writes is also used.
- A. Correct. A negative bit line assists the write.
- B. Lowering, not raising, the cell supply during a write makes the cell easier to flip.
- C. Lowering the word line weakens the access transistor and makes writing harder.