Subject :- VLSI Design

Topic :- MOS Circuit Design Styles

Difficulty :- Low

• To ensure read stability of the 6T cell shown below in Fig-4, the voltage across $M_8$ should be less than the threshold voltage when the charge on BLBAR is discharged through $M_8$ and $M_{11}$. Intuitively, read stability can be met by choose the size of $M_{8}$ to be greater $M_{11}$.

• The exact size of $M_{8}$ can be determined from the CR has to be greater than 1.2 to ensure read stability. A CR value of 1.5 is chosen for the design of 6T cell.

• To ensure write stability, the voltage across $M_{10}$ should be less than the threshold voltage when BL is pulled low to write a ‘0’ into the 6T cell. Similarly to read stability, the exact size of $M_{10}$ can be determined from the pull-up ratio (PR), where

• CR has to be at least less than 1.8 to ensure read stability. A CR value of 1 is chosen for the design of 6T cell.

• The end result of transistor sizing after stability analysis is shown below: $W_4 = W_5 = W_{10} = W_{11}$ minimum layout width $= 0.48µm W_8 = W_9 = 1.5\,\,W_5 = 0.72µm$