good layout in vlsi





a) In digital design, decide the height of standard cells you want to layout.It depends upon how big your transistors will be.Have reasonable width for VDD and GND metal paths.Maintaining uniform Height for all the cell is very important since this will help you use place route tool easily and also incase you want to do manual connection of all the blocks it saves on lot of area.

b) Use one metal in one direction only, This does not apply for metal 1. Say you are using metal 2 to do horizontal connections, then use metal 3 for vertical connections, metal4 for horizontal, metal 5 vertical etc…

c) Place as many substrate contact as possible in the empty spaces of the layout.

d) Do not use poly over long distances as it has huge resistances unless you have no other choice.

e) Use fingered transistors as and when you feel necessary.

f) Try maintaining symmetry in your design. Try to get the design in BIT Sliced manner.
Re: for a good layout in vlsi ?

Good lecture notes on cmos layout

cmos-layout-lecture-notes_01.pdf
Re: for a good layout in vlsi ?

One more lecture notes

cmos-layout-lecture-notes02.pdf
Re: for a good layout in vlsi ?

I want to know the reason of the 3rd tip:
Put as many substrate contacts in empty area as possible.
thx!

Re: for a good layout in vlsi ?

I think Andreas is wrong in somewhere with ” substrate contact as possible in the empty spaces of the layout. ”
Normally we are filling the empty space with decoupling capacitors .

Putting substrate contacts in empty space do not have any advantage , and have disadvantages like decrease the substrate isolation which will lead to more noise injection from the substrate.

disadvantage 2. You will make high ohmic substrate to low ohmic .

thanks
Augustin
Re: for a good layout in vlsi ?

Hi Rukia,
Thanks for your pointing the mistake. Already augstine explained the reason.
But I think I had gone through this topic in one of the analog layout book. not sure.
Sometimes it may be required as per the design rule to put more substrate contact , but
for a good layout this should be limited as per the layout rule.
Thanks augastine too
Andreas







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