Automatic via placement for power grid

Hi Wonyoung

"autoVia" function from IC615 does work across hierarchy. You can do it as follows:

a. Press "o" to invoke create-via form
b. Select "auto" mode at the top of the form
c. Enable "Check shape connectivity" option
d. Use middle-mouse button to drag an area for autovia to operate

Best regards
Quek

Hi Quek,

Thanks for your reply! I tried what you suggested, but when I enable "Check shape connectivity" the vias are not placed. When I disable that option, the vias are placed in every intersection within the area that I drag with my middle mouse button. My questions are:

1) Is it okay to leave the "check shape connectivity" option disabled? I was wondering what this option is for. 

2) Is there a way to create vias in only certain metal intersections? I tried putting labels on all of my wires (i.e. VDD, GND) and listed VDD GND on the "Net Name" or "Only for specified net" options, but that created vias in every metal intersection within the area I dragged with my middle-mouse button. I want to create vias only when two VDD metals or two GND metals intersect, not when VDD and GND metals intersect, to avoid VDD/GND short when creating a VDD/GND grid. 

Thank you very much!

Wonyoung 

Hi Wonyoung

The option is to prevent shorting of nets. Suppose we have a shape on net1 that overlaps another shape on net2.You would not want autoVia to add the via because this would short the net.

To prevent autoVia from adding unnecessary vias, you can disable the visibility of the unwanted layers in layer palette. autoVia would then ignore the intersection of those layers.

Best regards
Quek

Hi Wonyoung

You will have to use middle-mouse button a couple of times to select areas which you want autoVia to operate.


Best regards
Quek

Hi Quek,

How does Virtuoso know whether two shapes are for the same net or not? If I have metal1 and metal2 intersecting, can I simply label them the same to tell Virtuoso they should be connected?

Thank you very much. 

Wonyoung 

Hi Quek,

I think I might have found the solution. Just to check if this is the way to do it,

1) I created two shapes, one each with metal1 and metal2

2) opened Edit Path Properties -> Connectivity

3) wrote VDD in "Net Name"

After I did this, I could use the dragging the middle-mouse button to create vias. Do you think if this is the right way to do it? One problem I found with this approach is that it only works for flat designs. For example, if there are multiple cellviews instantiated in my layout and if I want to connect the VDD/GND of all these cellviews, I don't know how I can specify the "Net Name" of all the VDD/GND wires in different cellviews. 

Thank you very much.

Wonyoung 

Hi Wonyoung

Yes, it is the right way. You are right in saying that connectivity check is only for top level. It does not work across hierarchies. Sorry. : )  Would you pleaes file a service request with your local Cadence support and request for this enhancement?

Best regards
Quek

Hi Quek,

I just filed a service request. Thanks so much for your help!

Wonyoung