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cds_generic nmos extracting as 4-terminal

jmoriarty

Using IC6.1.5-64b.500.9.  

Instantiating "nmos" (not "nmos4") symbol view from "cds_generic" library in which the model field is populated with "mod".  It extracts as  follows:

M6 (0 0 0 0) mod

The symbol view has only 3 terminals, and there are only 3 terminals in the pin list. There appears to be an error in the "spectre" view, which shows 4 terminals.  Only fix is to copy "symbol" and "spectre" views to an editable library and delete a terminal from the "spectre" view.  If this is indeed an error, can it be corrected in the next release?  If there is already an open ticket I appologize for not finding it.

 Thanks.

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  • Quek

    Hi Jack

    Actually the situation is as follows:

    The nmos cell has only 3 terminals but will be netlisted as a usual 4 terminal mos device as requested by bsim model requirements. The 4th terminal (bulk) is hidden because it has been set as an inherited connection in the spectre view. If you open up the properties form of the "B" pin in the spectre view, you will find that the inherited property name is "bulk_n" and the default global net is gnd!.

    Inherited connection allows easy overriding of a net from the top level. E.g. if user does not specify the value of bulk_n property, the bulk terminal will be netlisted using the global ground "0". That's why you have "0" as the net name in your netlist.

    You can override the default gnd! as follows:
    a. Create a new schematic and place an instance of "nmos" from analogLib
    b. Open ADE and do spectre netlisting
    c. You will get "0" as the bulk net
    d. Now open up properties form of the nmos instance
    e. Add a "netSet" bulk_n property as shown below and set its value to "abc"
    f. Check and save the schematic
    g. Re-do netlisting using ADE
    h. You will now have (net1 net2 net3 abc) in the netlist and not (net1 net2 net3 0)

    Unless your spectre model file specifically uses 3 terminal model instead of 4 terminals, you should not remove the inherited connection in the spectre view. If you would like to specify the terminal net explicitly, you should use "nmos4" cell instead of "nmos" cell.

    Hope that this clears up the issue. : )

    Best regards
    Quek

Reply
  • Quek

    Hi Jack

    Actually the situation is as follows:

    The nmos cell has only 3 terminals but will be netlisted as a usual 4 terminal mos device as requested by bsim model requirements. The 4th terminal (bulk) is hidden because it has been set as an inherited connection in the spectre view. If you open up the properties form of the "B" pin in the spectre view, you will find that the inherited property name is "bulk_n" and the default global net is gnd!.

    Inherited connection allows easy overriding of a net from the top level. E.g. if user does not specify the value of bulk_n property, the bulk terminal will be netlisted using the global ground "0". That's why you have "0" as the net name in your netlist.

    You can override the default gnd! as follows:
    a. Create a new schematic and place an instance of "nmos" from analogLib
    b. Open ADE and do spectre netlisting
    c. You will get "0" as the bulk net
    d. Now open up properties form of the nmos instance
    e. Add a "netSet" bulk_n property as shown below and set its value to "abc"
    f. Check and save the schematic
    g. Re-do netlisting using ADE
    h. You will now have (net1 net2 net3 abc) in the netlist and not (net1 net2 net3 0)

    Unless your spectre model file specifically uses 3 terminal model instead of 4 terminals, you should not remove the inherited connection in the spectre view. If you would like to specify the terminal net explicitly, you should use "nmos4" cell instead of "nmos" cell.

    Hope that this clears up the issue. : )

    Best regards
    Quek

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