How to different drive strength standard cells?

[BB11]

How to draw different drive strengths (2x, 4x) in standard cells?

Hi

Could anyone please show me how to draw a and gate with 2 inputs and different drive strengths of 2x,4x...pls!

Thanks
BB

 

[chris.mourad]

Hi

Basically the AND gate is made of a NAND gate + an inverter stage.
Usually the NAND gate transistor sizes are common to all drive strengths, and the inverter stage has an adapted drive strength.

For example:
- x1 : has an inverter stage with NMOS with W=1u and PMOS with W=2u
- x2 : has an inverter stage with NMOS with W=2u and PMOS with W=4u
- x4 : has an inverter stage with NMOS with W=4u and PMOS with W=8u

etc...

 

[BB11]

Hi Chris

Thanks for your reply. So I dont need to add anther nand gate from the output of the 1 st nand gate?
I assumed that I need to have 2 outputs from the first Nand Gate and each output will have a nand gate respectively.

Looking forward for your reply.

Thanks
BB

 

[chris.mourad]

Hi

No this is not needed because: the NAND is driving the output INVerter which gives the drive strength.

Cheers

 

[BB11]

Hi

No this is not needed because: the NAND is driving the output INVerter which gives the drive strength.

Cheers

same things applied to AND,OR as well right?

 

[chris.mourad]

Hi

AND GATE = NAND + INV
OR GATE = NOR + INV

now the NANDx2 gate differs from the NANDx1 gate in that the transistors have typically a size (W/L) 2 times bigger