Hierarchical Parasitic Extraction & Cadence Tools

Hi Jimito13

First, a minor correction. it is not correct to say "perform hierarchical RCX with the Hierarchy Editor". It is not possible to do hierarchical RC extraction using the Hierarchical Editor (HE). It is meant for controlling the views to use for simulation netlisting, not parasitic extraction. Parasitic extraction can only be done using QRC parasitic extractor. I think you meant to say "perform mixed views simulation with the Hierarchy Editor".

You can do it as follows:
a. Do hierarchical Assura LVS for layout cell "A" with ?preserveCells avParameters option. The cell file should contain B1, B2, C1, C2, C3, C4, C5 & C6
b. Do hierarchical parasitic extraction with "excluded nets proper" option using QRC. Except for the required nets (e.g. C5-C6), exclude all other nets for RC extraction
c. Create testbench schematic "myTB" with cell A in it
d. Create a config view for "myTB" using HE
e. In HE, set views of A, B2, C5 and C6 as "av_extracted"
f. Do simulation using config view in ADE-L or ADE-XL

This should give you what you want. : )  It takes a bit of time to exclude the unwanted nets but there is no choice because hierarchical extraction only works with "excluded nets" and "excluded nets proper" options.

"excluded nets" option gives you R for the non-excluded nets and C on all nets. "excluded nets proper" options gives you RC on only the non-excluded nets. Please refer to $QRC_HOME/doc/qrcxUser/qrcxUser.pdf for more details.

Best regards
Quek

Hello Quek,

Thanks a lot for your helpful feedback :-) You are absolutely right with your first paragraph,QRC performs the extraction procedure and not HE,i formulated it wrong in my first message.I have a couple of additional questions before closing this topic.

1. ?preserveCells gives a drop-down menu with File & Cells choises.What should i select?Sould i syntax a file and input it into Assura via the menu below or i can insert the names of the cells manually?I would appreciate if you could send me a screenshot as an example or an example syntax of a file.

2.The Vss rail of my circuit is one and common to all cells from the lowest level to the top level via various interconnections from level to level.Is it possible to exclude it from extraction of some specific cells and not from others?I suppose that it is not feasible since in reality Vss i one entity (irrelevantly if it is created from Vss cables of individual low level cells and the interconnections among them) but i am wondering if there is a technique to cheat Assura QRC and make the selective extraction i desire...

Thanks in advance.

Best Regards,

Jimito13

Hi Jimito13

You can enter the names in a file if there are lots of cells to preserve. It would be easier editing a file. E.g. for spef/dspf flow, we can use SKILL to grap cellnames from the layout, dump them into a file and then use that file for ?preserveCells. If there are just a few cells to preserve, you can just enter them in the form.

It is possible to do the selective extraction of RC for a net but it would be quite an elaborate scheme that requires re-compilation of QRC tech directory with -res_blocking and -blocking options. Appropriate marker layers would most likely also have to be added to the layout in order to do the blocking. I think it is not really worth the effort. : )

Best regards
Quek

What you should see on the form:

Quek,

I do not know how to thank you..You have helped me a lot up to now and the least i can say is a BIG THANKS :-)

One final question.What is the difference between Cells & Exclude Cells White Boxes that i must fill in at the above ?PreserveCells option's form.

Thanks in advance again :-)

My Best Regards,

Jimito13

Hi Jimito13

You are welcome. : )

Assuming that you have cells A1, A2 and A3. If you enter only "A1" in "Cells" box, it means only cell A1 will be preserved. "Exclude" box is used to exclude specific cells when wildcards are used in "Cells" box. E.g. you have entered "A*" in Cells box to save a little typing but actually you do not want cell A1 to be preserved. In this case, you will also need to enter "A1" in Exclude box.

Best regards
Quek

Ok,for wildcards case i got it.For the example i gave you above,with the multiple cells of the hierarchy,if i fill in the cells B1,B2,C1,C2,C3 in the Cells box and the cells C4,C5,C6 in the Exclude Cells box,this means that LVS will be executed on B1,B2,C1,C2,C3?And how this choise affects the next step that is QRC?I am a little bit confused,sorry if i become annoying...

Thanks in advance.

My Best Regards,

Jimito13

It does not mean that lvs will be executed only on B1, B2, C1, C2 and C3. It means that during lvs, only cells B1, B2, C1, C2 and C3 will be preserved. During lvs, cells might sometimes be promoted to a higher level of hierarchy in order to match the schematic. As such, the cell will no longer be present in the final lvs database. This would create a problem for hierarchical QRC extraction because QRC works on the lvs database and if there are no cells in it, it would not be possible to do a hierarchical extraction. QRC normally gives a flat output unless hierarchical extraction is selected.

Hence in order to do QRC hierarchical extraction, the cells have to be present in the lvs database and in order to ensure that they are present, we use ?preserveCells option. You should not enter C4, C5 and C6 in the Exclude box because we want them to be preseved too. Otherwise you will not get the full cell hierarchy from QRC. C4, C5 and C6 should also be entered in the Cells box. You can then choose to use "av_extracted" or "schematic" for these cells in the Hierarchy Editor.

Best regards
Quek

Ok Quek,everything is clear now!Thank you once more for your time to answer my questions and for your precious help :-)

My Best Regards,

Jimito13

Good Morning Quek,

I am gonna need your precious advice one more time.When a create a config view with HE in order to post simulate my circuit with mixed views (that is : schematic for cell A,av_extracted for cell B,schematic for cell C etc...),how the interconnection among various cells are considered by the simulator?Are they taken as ideal like in a schematic only simulation or real as designed in the layout of the top level cell that contains all the individual sub-cells?

Thanks a lot in advance.

My Best Regards,

Jimito13