How to export GDS file of PCell instance (submaster)

You can't directly stream out a subMaster, but either way you've got to generate that subMaster somehow - and that means instantiating the PCell in a layout cellView (it doesn't need to be a "temporary library") and then streaming out the cellView containing those instances.

The simplest way would be to take the schematic you have which has the sets of variant parameters you want, and then Launch->Layout XL, create a new cellView, and then in that use Connectivity->Generate->All From Source and generate all the instances corresponding the to schematic. Save this layout and then stream that out.

Andrew

Thank you, Andrew. One thing I noticed with your suggestion is that after creating a layout cell view and calling generate->all from source, the Skill code in the other post from you that I referenced above worked, reporting the parameters for all the variants. So I see that querying pcell properties from a layout is different than querying from a schematic.

After generating the new cell view, I was able to generate a GDS file of the whole schematic with File->Export Stream from VM (not what I wanted but good to know about). I also found that I could right click a cell in the layout view and do Hierarchy->Make cell. Then I could use File->Export->Stream from the console window and specify the new cell name that I had just set to export a single cell as a GDS (what I had wanted).

I want to automate this so I will hunt down the Skill commands for these steps and walk the variants like the code in your other post I linked to. A couple questions about this:

1. Is Hierarchy->Make cell the best way to export the GDS for a cell or is there another way to make a variant a top level cell for export?

2. So I will generate a new layout for the library to export the pcell GDS files. Can that be an expensive step? I am wondering if I should remove the layout afterwards or if it could be used again if a user modifies the schematic and wants to re-run my export function.

There are several things to unpick in this post, so let me quote sections of your last reply and respond to them in turn. What you're trying to do here seems rather odd.

wsha said:

One thing I noticed with your suggestion is that after creating a layout cell view and calling generate->all from source, the Skill code in the other post from you that I referenced above worked, reporting the parameters for all the variants. So I see that querying pcell properties from a layout is different than querying from a schematic.

That's because that code only prints pcell parameters, and the symbols are unlikely to be be pcells (symbol pcells are a thing, but they're normally only needed if you want the symbol to have variable pins or appearance). So commonly you'd have a static symbol with a set of parameters, and those parameters get transferred to a layout pcell when you use generate all from source in VLS XL.

wsha said:

After generating the new cell view, I was able to generate a GDS file of the whole schematic with File->Export Stream from VM (not what I wanted but good to know about).

If you'd saved the resulting cellView, you could have used stream out from the command line or Export Stream without the VM option turned on. I'm not quite sure why this would not be what you wanted...

There's no such thing as a "GDS file of the whole schematic" since GDS is a storage format for layout and not for schematic data, so odd terminology here.

wsha said:

I also found that I could right click a cell in the layout view and do Hierarchy->Make cell. Then I could use File->Export->Stream from the console window and specify the new cell name that I had just set to export a single cell as a GDS (what I had wanted).

Yes, you could do that.  The approach I mentioned above would have given you a single GDS file with multiple cells in it. I'm not really sure why you would really want each variant in a separate stream (GDS) file - you've not really explained why that's important

wsha said:

1. Is Hierarchy->Make cell the best way to export the GDS for a cell or is there another way to make a variant a top level cell for export?

Given this is a rather weird thing to want to do - exporting a stream file of a single variant - then it's hard for me to comment as to whether it's the "best" way to export this. There's no direct way of exporting a single variant only. It rather depends on what you're trying to do with the resulting stream file I guess.

wsha said:

2. So I will generate a new layout for the library to export the pcell GDS files. Can that be an expensive step? I am wondering if I should remove the layout afterwards or if it could be used again if a user modifies the schematic and wants to re-run my export function.

I struggle to understand why somebody would want to keep exporting GDS for each variant of a pcell, and whether it's expensive or not depends on how often you would re-generate this from a schematic (or why on earth you'd do it in the first place).

Andrew

Here is some background of what I am trying to do. We are using Cadence for design and layout of devices. In the initial design phase, we will run RF simulations of the schematic with Spectre while iterating on component parameters. However, some of the components which are specified as PCells (which I generalized as all PCells in previous posts; I will figure out how to filter out the necessary cells) need to be simulated with an external tool in order to determine their RF parameters. The way the information will flow is that a GDS file of the component will be input into an external tool and then the resulting S-parameters will be read back into Cadence and attached to the netlist (I think that is where it goes) for the RF simulation. There will be some iteration of PCell parameters and RF simulation. Once the parameters are determined, a final layout can be generated.

My goal is to automate the process of sending the GDS files from the schematic to the external tool and receiving the S-parameter data back.

Andrew Beckett said:

That's because that code only prints pcell parameters, and the symbols are unlikely to be be pcells (symbol pcells are a thing, but they're normally only needed if you want the symbol to have variable pins or appearance). So commonly you'd have a static symbol with a set of parameters, and those parameters get transferred to a layout pcell when you use generate all from source in VLS XL.

Okay, so the instances in the schematic are not PCells. I found that I can access the parameters of the components in the schematic with cdfGetInstCDF and then looking at the "parameters" property. This answers what I was trying to ask at the beginning of my original post of how to get the parameters of a component in a schematic (which I called a PCell but maybe is not a PCell until it is part of a layout). Currently, one approach I am considering is looking up the parameters with cdfGetInstCDF and generating layout cells to stream out with dbOpenCellViewByType, and the other approach is the generate all from source method.

Andrew Beckett said:

There's no such thing as a "GDS file of the whole schematic" since GDS is a storage format for layout and not for schematic data, so odd terminology here.

Yes, that was sloppy language on my part. I was able to generate a GDS file of a layout of the schematic. Since I am not interested in the layout of the whole device at this stage, I wasn't thinking about that layout too concretely.

Andrew Beckett said:

Given this is a rather weird thing to want to do - exporting a stream file of a single variant - then it's hard for me to comment as to whether it's the "best" way to export this.

Regarding the "best" way to do this, the main factors I was thinking about were speed, volume of code, and robustness. For speed, I don't know yet if anything is slow enough to worry about, but only generating GDS files of the components that were modified rather than all components might be one example. For volume of code, using a small number of built in functions would be better than writing a larger amount of my own code. For robustness, perhaps making the fewest modifications to the schematic's library would be best.

Andrew Beckett said:

I struggle to understand why somebody would want to keep exporting GDS for each variant of a pcell, and whether it's expensive or not depends on how often you would re-generate this from a schematic (or why on earth you'd do it in the first place).

I only need to export the GDS of a variant once as long as it does not change. However, that requires that I can track when it changes. If it is okay speed-wise, I could generate all GDS files each time and try to deduplicate the simulation work keeping track of which GDS file content has been previously simulated. Also, I am not sure if the generate all from source method will require generating the layout for the full schematic each time.

I think it's highly unlikely that the time taken to create an instance with the right parameters and streaming it out will be the bottleneck in the process - if you're using some kind of electromagnetic simulator, that will probably be the time-limiting part. So you may want to do some caching to avoid re-creating/streaming-out/re-simulating something for that reason.

The generate all from source is unlikely to be the slow part either. Anyway, hopefully you can figure this out now - whether you do it that way or create a layout and instance yourself with the same parameters.

Andrew 

I think it's highly unlikely that the time taken to create an instance with the right parameters and streaming it out will be the bottleneck in the process - if you're using some kind of electromagnetic simulator, that will probably be the time-limiting part. So you may want to do some caching to avoid re-creating/streaming-out/re-simulating something for that reason.

The generate all from source is unlikely to be the slow part either. Anyway, hopefully you can figure this out now - whether you do it that way or create a layout and instance yourself with the same parameters.

Andrew