[SOLVED] Creating a Custom Resistor for an IC, How to Connect?

[memoslw]

Fellow IC designers,

I have a BGR design where I use 5 resistor instances in the circuitry. I want to interdigitate these resistors, however, It is not possible to do this automatically through Virtuoso. I have looked at MODGEN, but for a true interdigitated resistor, I need the fingers of the resistors to come one after another. More information and questions are below, any help/info would be really appreciated:

• I have 5 resistor instances (A, B, C, D, E), each of these resistors consists of 5 poly silicon strips connected in series. When generated from the schematic of the BGR circuit, these resistors are created separately, as usual, where each of them has 5 series strips connected together through the metal layer. Because of that I have made a custom layout for an interdigitated resistor design. The pattern of this resistor layout is ABCDEABCDEABCDEABCDEABCDE, later on these strips are connected in series accordingly (A is connected in series to the next A, and so on...) through the metal layers. By this way, I have one huge resistor instance which is interdigitated, which I thought would be better for matching purposes. Does this practice make sense in terms of matching resistors?
  
  
• How can I add this custom resistor to the schematic of the BGR circuit? In the end, I have to do LVS and then the parasitic extraction, the custom resistor have no connection to the other instances in the circuit right now. Is there a way to edit connectivity so that I can pass the LVS check and then the parasitic extraction?
  
  
• As I said before, I have checked the MODGEN in Virtuoso, but it doesn't seem to really interdigitate the resistors, it rather puts them next to each other. I would like to hear your MODGEN experiences with resistors. I found it not very helpful in terms of the resistor matching, but useful for the transistor matching.
  

That is all I could think of right now, I can provide more information as soon as it's needed. Thank you all in advance!

 

[dick_freebird]

What's wrong with making a schematic view with the resistors
represented one per segment, arranged as you wish it to be
laid out?

It's a good way to document intent forward if you don't own
the whole chain of effort through verification and "tape-out".

 

[memoslw]

What's wrong with making a schematic view with the resistors
represented one per segment, arranged as you wish it to be
laid out?

It's a good way to document intent forward if you don't own
the whole chain of effort through verification and "tape-out".

I guess there is no problem with that. I am just unsure/don't know how to test my circuitry with my custom created resistor. How can I "tell" Virtuoso that the resistor I have created is actually the resistors presented in the schematic?

 

[dick_freebird]

At is simplest, LVS the resistor-bed layout against the
resistor-bed schematic. You just need pins on the layout.

You don't "tell" LVS what's what unless it runs into trouble.
Then you can add correspondences. But a series string or 5
of 'em, if properly pin-tagged, should not be at all confusing.

 

[memoslw]

At is simplest, LVS the resistor-bed layout against the
resistor-bed schematic. You just need pins on the layout.

You don't "tell" LVS what's what unless it runs into trouble.
Then you can add correspondences. But a series string or 5
of 'em, if properly pin-tagged, should not be at all confusing.

The problem I have right now is the pin designation since the terminals of the resistor I have designed are electrically connected. When I create one of the pins for the resistor, the pin designation 'propagates' through the resistor and sets the same pin designation to the resistor output. How can I set the input and the output pins of the resistors properly? I will share what I have done here if I can solve the problem.

 

[memoslw]

At is simplest, LVS the resistor-bed layout against the
resistor-bed schematic. You just need pins on the layout.

You don't "tell" LVS what's what unless it runs into trouble.
Then you can add correspondences. But a series string or 5
of 'em, if properly pin-tagged, should not be at all confusing.

I have "solved" the issue. I just added pins for the input and output of the resistor and then deleted the warning markers for shorts through the Annotation Browser. I then added the custom resistor to my BGR layout and used 'Define Device Correspondence' option from the 'Connectivity' menu for assigning the pins to the nets. Thank you for your assistance!