What does the layout word refer to?

I'm getting a bit confused these days about the word "layout"
is it the making of the mask layers for the IC ?
or is it the process of floorplanning and place & route ?

or are they at the end allll extensions to each other???

in an ASIC, when exactly do I do the mask layout for each transistor?
when it's a small design, or it's always done this way....???

should i see the P&R plan then do according to it the mask layout or what?

I'm confused about terminology and hierarchy of steps


thanks,
Salma

layout

hi, I am beginer of layout. As I know, the basic layout is draw each transistor by youself.But now,we have some EDA tools such SE/Astro,this tools can auto P&R.

Re: layout

salma ali bakr said:

I'm getting a bit confused these days about the word "layout"
is it the making of the mask layers for the IC ?
or is it the process of floorplanning and place & route ?

or are they at the end allll extensions to each other???

in an ASIC, when exactly do I do the mask layout for each transistor?
when it's a small design, or it's always done this way....???

should i see the P&R plan then do according to it the mask layout or what?

I'm confused about terminology and hierarchy of steps


thanks,
Salma

Click to expand...

in an ASIC design you'll only do layout design (I am talking in digital context) when you are designing a standard cell.and in place and route you are just placing these already designed cells and making interconnection between these cells...and about the rest of your questions...(placement-just placing these cells
routing - making interconnection between these cells)..

Re: layout

ahaaaa
so i do the "each single transistor" layout when it's just the first time to do this design (full custom), cause there isn't a previous designed cell to be placed nor routed....but if the cells are already there (standard cells), then obviously i just need to connect them and no need for the making of their masks since they're already ready in the fab of course

what are the output file types of each stage please?

thanks,
Salma

Re: layout

vary a lot....layout is always gds,sometimes tool specific format also as Magma gives lava(they are very inspired by the geographical terms I guess) as output ..
but it is not easy to give you view list..can you please streamline it to some specific design steps...

layout

hello salma

at every stage the layout file is given out as .gds only . along with other files like .lef or .sdf or .spef ./.many files are generated at this stage for various verfication like timing.

Suresh

Re: layout

i was just confused about the fact that we say layout about p&r and also about the mask layout
but now i know the difference between them, for instance if i have a full custom ASIC, i'll be doing the mask layout for my cells (cause they'll be somehow unique) and then i'll generate a symbol (i guess) which is then used in a library for the p&r tool (if it isn't custom then the p&r tool will use the fab standard cells)...
and if i have a standard cell ASIC, then i won't need to do the mask layout for my cell cause they'll be already designed by the fab

and now also i know that it's usually a GDS extension for layout (representing the geomertical shapes and the labels of the layout)....but for p&r ? what's the output ? is it also GDS or any other tool specific extension or something else???

am i missing something guys? or confusing stuff?

Salma

Re: layout

salma ali bakr said:

i was just confused about the fact that we say layout about p&r and also about the mask layout
but now i know the difference between them, for instance if i have a full custom ASIC, i'll be doing the mask layout for my cells (cause they'll be somehow unique) and then i'll generate a symbol (i guess) which is then used in a library for the p&r tool (if it isn't custom then the p&r tool will use the fab standard cells)...
and if i have a standard cell ASIC, then i won't need to do the mask layout for my cell cause they'll be already designed by the fab

and now also i know that it's usually a GDS extension for layout (representing the geomertical shapes and the labels of the layout)....but for p&r ? what's the output ? is it also GDS or any other tool specific extension or something else???

am i missing something guys? or confusing stuff?

Salma

Click to expand...

there is no symbol as such for gds you will use it as a whole(otherwise debugging will becomes very hard)...The standard output of the place and route tool is gds-graphics data system (tapeout)...But several tools have their internal databases which is mostly used when you are working on a tool and not sure whether you'll go for tapeout or not...Or some other pnr optimization have to be applied....

Added after 1 minutes:

the reason for this is gds stream-in and stream-out is cpu intensive tasks..

Added after 15 minutes:

just for your reference (gds as viewed in a viewer):

layout

hello salma

please check the following link . may be u can get a good picture of P&R steps.

**broken link removed**

BEST OF LUCK

Suresh

Re: layout

Hi Suresh,
can you please share some more links???
Thanks...

layout

hello deh

There are lot of simple tutorials thse are mostly university slides .. i will try to send u more .. but from ur side i suggest u to look into the uni slides which offer vlsi courses ..

Best of luck
suresh

Added after 2 minutes:

**broken link removed**

**broken link removed**

**broken link removed**

layout

Hi
full custom or standard cell designing is done only if the previous library cells could not meet your design characteristics like performance,power etc..,
If the previous library of cells could meet your design specifications then u need not go for designing the cells again, instead you can go for the existing ones.
hope this makes it clear.

Re: layout

pratap_v said:

Hi
full custom or standard cell designing is done only if the previous library cells could not meet your design characteristics like performance,power etc..,

Click to expand...

Well, I guess you meant only Full Custom
cause Standard Cell means you use the "already existing" cells


Thanks,
Salma

Re: layout

salma ali bakr said:

pratap_v said:

Hi
full custom or standard cell designing is done only if the previous library cells could not meet your design characteristics like performance,power etc..,

Click to expand...

Well, I guess you meant only Full Custom
cause Standard Cell means you use the "already existing" cells


Thanks,
Salma

Click to expand...

no it applies for both......

Re: layout

I don't understand
explain please
this is getting confusing !!!!

Re: layout

can you elaborate what thing is confusing you..........

Added after 2 minutes:

as pratap says:

pratap_v said:

full custom or standard cell designing is done only if the previous library cells could not meet your design characteristics like performance,power etc..,

Click to expand...

you can consider it full custom in case of ASIC-design(SOC or whatever design you have) and redesign in case of standard cells...

Re: layout

Full custom is when you do every single thing from scratch, right? Cause it's all unique and you need to meet certain constraints that aren't available otherwise

Semi custom has two types:
-Standard Cells: when you already have the cell libraries available and you just need to do the placement and the routing
-Gate Arrays: when you have the cells already placed and you just need to do the routing (interconnections)

He was just referring to Full Custom and Standard Cells as one thing
so I wanted to know his point of view and explain that it isn't the same

Re: layout

salma ali bakr said:

Full custom is when you do every single thing from scratch, right? Cause it's all unique and you need to meet certain constraints that aren't available otherwise

Semi custom has two types:
-Standard Cells: when you already have the cell libraries available and you just need to do the placement and the routing
-Gate Arrays: when you have the cells already placed and you just need to do the routing (interconnections)

He was just referring to Full Custom and Standard Cells as one thing
so I wanted to know his point of view and explain that it isn't the same

Click to expand...

Standard cell are designed using full-custom techniques...
I think pratap wants to specify that when you dont have standard cell library meeting the requisite performance parameters than you have to redesign the library (In case of module designer you only have to wait for circuit designer to complete it for you)......
As of now only very high performance circuits like microprocessors are designed using full-custom techniques.....
You can also take the advantage of full-custom (mixed signal techniques) where you have some blocks designed using standard cells and for very critical blocks you design each and every gate on your own and then integrate it on the chip manually(i dont know the exact details of mixed signal,may be some designer working on this domain may define it more clearly)......

Lets have an example :
Consider you have to design a chip (lets say for low power application),you'll look for all the alternatives available (full,semi)..Done some analysis stuff.. you'll find that you are losing a lot by going for semi-custom (you are gaining on TAT but performance is affected badly)..Then you'll start doing full custom..divide the cicuit in blocks draw the schematic ,simulation ,layout,post-layout simulation (after parasitic extraction),cross-talk anlaysis and then tape-out.Number of steps may vary.....

Now you want to know where the full-custom and Standard cell is different.no difference at all...this module can be used in the same way as a Standard cell (provided you have all the information regarding this module ,timing ,power,noise,etc..)you can define the functionality (number of timing arcs )and integrate it using semi-custom techniques in a large design, but the condition is this module can qualify for the requirement.. ...
In simple words designing NAND Standard cell for using in semi-custom techniques is same as you are designing a memory or microprocessor....

Re: layout

ok, it's obvious that Standard Cells are already done by using Full Custom techniques, they have to be available in the first place

But it's my first time to know that I can change in the standard cells, I thought it'd be much easier to change the library as a whole...But how can you change in the cells themselves, aren't they sort of IPs that can't be accessed, you just use them? Can you really change them???

Thanks,
Salma
PS: I always hit the Help Button
don't worry
I'm generous..LOL

Re: layout

its not a simple procedure to change the library ...you have to very clear about the development flow for that library...If this library is designed by some other division from your company then you are always free to ask them to made changes you want...like change the process technology from generic to low-power...