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manruru
Joined: 10 Mar 2008
Posts: 11
Helped: 1
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 25 Sep 2008 9:33 what happens if we dont follow the grid and snap spacing. |
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Hi all,
plz dont think that it is a stupid questions.
what happens if w dont follow the grid and snap spacing while doing laying out the devices.
will there be any impact while fabricating?????
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pbs681
Joined: 19 Aug 2004
Posts: 154
Helped: 11
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| 25 Sep 2008 13:04 Re: what happens if we dont follow the grid and snap spacing |
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| manruru wrote: |
Hi all,
plz dont think that it is a stupid questions.
what happens if w dont follow the grid and snap spacing while doing laying out the devices.
will there be any impact while fabricating????? |
no no, this is not a stupid question....
first of all, snap spacing should follow grid. so, the only issue is only grid spacing. If you draw layout with smaller than grid, then during fabrication, it will snap to the grid. this will cause a problem where u will not get what u draw. Besides, the OPC and mask writing process will have problem if u have such grid size. So, in summary, the grid size is very important issue that u have to deal with.
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rfsystem
Joined: 25 Feb 2002
Posts: 797
Helped: 85
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| 25 Sep 2008 21:33 Re: what happens if we dont follow the grid and snap spacing |
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The layout data coordinates should lay on a grid defined by the mask maker. Today typical 10nm or 5nm but depend. It will be checked before accepting GDS2 data. No way if not on the grid.
Here a smart hint:
Use for your own layout a greater grid. If you browse the design rules you can possible use a more unified grid. 10 years ago it was very easy to layout in lamda-rules. Today every nm is squeezed, layout is a mess. If you use own personal grid setting 2x then you can place contacts and paths still in the middle.
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chikva
Joined: 06 Feb 2008
Posts: 4
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| 29 Sep 2008 6:00 Re: what happens if we dont follow the grid and snap spacing |
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can someone please explain about snap spacing?
how is it related to grid spacing?
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erikl
Joined: 09 Sep 2008
Posts: 20
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| 29 Sep 2008 18:37 what happens if we dont follow the grid and snap spacing. |
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chikva asked:
can someone please explain about snap spacing?
how is it related to grid spacing?
Snap spacing controls the possible locations where you can act. It can be adjusted independently of the grid spacing, with arbitrary integer multiples or fractions relative to it. For layout, you could adjust snap spacing a factor 2 bigger than grid spacing, so you can keep the original grid, and still follow rfsystem's suggestion above.
For schematics, I normally use snap spacing with a fraction of 4 in relation to grid spacing. Thus I get 3 more access points (in one direction) between the shown grid.
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chikva
Joined: 06 Feb 2008
Posts: 4
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| 01 Oct 2008 8:15 Re: what happens if we dont follow the grid and snap spacing |
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what we will be giving to the foundry is the final gds2 only right?so does the grid of schematics mattter?
Also in the dispaly options am using i can see
Xminor spacing,
Y minor spacing ,
X snap spacing and
Y snap spacing.
Does that imply that my grid is half the snap spacing or is that grid and snap spacing here are the same?Also what does X minor spacing and y minor spacing imply?
(Am using cadence virtuoso)
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erikl
Joined: 09 Sep 2008
Posts: 20
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| 02 Oct 2008 13:07 Re: what happens if we dont follow the grid and snap spacing |
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| chikva wrote: |
what we will be giving to the foundry is the final gds2 only right?
so does the grid of schematics mattter?
Of course not. This was thought as an example only.
Also in the dispaly options am using i can see
Xminor spacing,
Y minor spacing ,
X snap spacing and
Y snap spacing.
Does that imply that my grid is half the snap spacing or is that grid and snap spacing here are the same?Also what does X minor spacing and y minor spacing imply?
(Am using cadence virtuoso) |
By minor & major spacing you can define 2 different SHOWN grids (dots or lines). Depending on your current zoom, either the minor (layer: grid drw) or the major grid (layer: grid dr1, a bit brighter) is shown.
The snap spacing defines the points where you can act on, i.e. define corners or start/end points of lines. This should be set to the (minimum) grid size set for the process by the fab - or a factor 2 above, to be on the safe side, as stated in the posts before.
(Personal) example: If the minimum grid size of the process, e.g., is 0.1 (prescribed by the fab for the given process), I normally adjust the minor spacing to this size (0.1) so I can see the minimum legal grid points when zooming in to the grid, the major spacing a factor of 10 above, i.e. to 1, and the (X & Y) snap spacing to 0.2. Normally, I draw all the polygone points on this 0.2*0.2 grid. Thus I have 5-1=4 additional access points (in each of the orthogonal directions) between 2 visible points of the shown major grid. If - later on - it should be necessary to access a (legal) point on the 0.1*0.1 grid, this can still be done by (evt. temporarily) resizing the snap spacing to 0.1 .
Hope, this is not too confusing!  - erikl
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