Large gds file

[Sharon Oh]

I am having problems streaming my layout to gds. I have a very simple
unit cell, which is a pcell with just two circles. Within this pcell,
I have set x and y repetition. This generates a lot of circles
(almost
a million polygons) in the final layout. When I export to gds, the
file is large (around 600 Meg). Is this normal? The file is a bit
unwieldy to ftp... is there any way to reduce its size (before zipping
it, that is)?

Sharon

[Roger Light]

Sharon Oh wrote:

I am having problems streaming my layout to gds. I have a very simple
unit cell, which is a pcell with just two circles. Within this pcell,
I have set x and y repetition. This generates a lot of circles (almost
a million polygons) in the final layout. When I export to gds, the
file is large (around 600 Meg). Is this normal? The file is a bit
unwieldy to ftp... is there any way to reduce its size (before zipping
it, that is)?

By default, pcells are flattened when they are exported as gds2 (gds2
does not support the notion of pcells). This means your simple pcell
with repetitions becomes a very large layout cell that does not take
advantage of the redundancy of your design.

Would it be possible to simply create a mosaic of your two circle pcell?
Obviously this depends on how your repetition works.

If you can do this, the gds2 file will contain one structure that is
your pcell and another structure that is the mosaic and will hence be
much smaller. Your current gds2 file effectively has a million
structures whereas what I have proposed would have two.

Hope this helps.

Regards,

Roger

[gennari]

I assume you want to change the size or other parameters of the circles, and
that's why you made them into pcells. If this is the case, then I don't
think you can use a mosaic (array). However, an instance (SREF) in GDSII
takes around 60 bytes, so you either have more like 10 million circles or
the circles themselves are being flattened. There are two things you can try
to reduce file size if you cannot use a mosaic:
1. Make the cellname as short as possible. GDSII stores the cellname in each
instance, and if the cellname is long then that name (duplicated at least a
million times in the GDSII file) probably takes up much of the size. GDSII
is so inefficient.
2. Gzip the GDSII. Gzip typically has a 5.5:1 compression ratio, but because
your file is so regular then the ratio may be 10:1 or more. It's always a
good idea to gzip a lage file such as a GDSII layout before sending it to
someone.

Also, the circles will likely be written as polygons with a large number of
vertices. I believe it is legal to represent circles as singe point paths
with rounded corners, but I don't know if Cadence does/can do this.

Frank

"Roger Light" <roger.lightDOESNTLIKESPAM@nottingham.ac.uk> wrote in message
news:ckj31q$hor$1@oyez.ccc.nottingham.ac.uk...

Sharon Oh wrote:

I am having problems streaming my layout to gds. I have a very simple
unit cell, which is a pcell with just two circles. Within this pcell,
I have set x and y repetition. This generates a lot of circles (almost
a million polygons) in the final layout. When I export to gds, the
file is large (around 600 Meg). Is this normal? The file is a bit
unwieldy to ftp... is there any way to reduce its size (before zipping
it, that is)?

By default, pcells are flattened when they are exported as gds2 (gds2
does not support the notion of pcells). This means your simple pcell
with repetitions becomes a very large layout cell that does not take
advantage of the redundancy of your design.

Would it be possible to simply create a mosaic of your two circle pcell?
Obviously this depends on how your repetition works.

If you can do this, the gds2 file will contain one structure that is
your pcell and another structure that is the mosaic and will hence be
much smaller. Your current gds2 file effectively has a million
structures whereas what I have proposed would have two.

Hope this helps.

Regards,

Roger