How to determine capacitance of input pin with spectreS

Discussion in 'Cadence' started by Thomas Popp, Jul 21, 2003.

  1. Thomas Popp

    Thomas Popp Guest


    Can anyone give me a hint how I determine the capacitance of an input
    pin of a standard cell (extracted netlist) with spectreS?

    Thanks in advance for any help.

    Thomas Popp, Jul 21, 2003
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  2. Thomas Popp

    S. Badel Guest

    watch the net-list and add all capacitances connected to that node.
    S. Badel, Jul 23, 2003
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  3. Thomas Popp

    Thomas Popp Guest

    You mean I have to do it by hand??? Or is there a function in spectreS
    (OCEAN) which does the trick automatically? I've heard that a typical
    SPICE simulator is able to calculate the capacitance of every node of a
    given netlist. So I strongly presume this is also possible with spectreS...

    Thomas Popp, Jul 23, 2003
  4. Thomas Popp

    S. Badel Guest

    don't know any special function. However, if you want to compute
    the parasitic capacitance at the input of a cell, you can do the following.

    open layout & schematic views
    run extraction on layout, then LVS
    LVS must be successful
    then, on LVS window select "parasitic probe", push "whole net" and select a
    net in
    the schematic. This will add up all parasistics and display the result.
    However, it non-parasitic capacitors won't be taken into account.
    hope this helps,
    S. Badel, Jul 24, 2003
  5. Thomas Popp

    Marc Heise Guest


    I think you are looking for the "captab" function of spectre. Here is an
    example how to include it in a netlist for a DC run (it is not in the gui
    yet, so you might load it over an include file ):

    dcOp dc write="spectre.dc" maxiters=150 maxsteps=10000 annotate=status \
    capinfo2 info what=captab where=file file="capnodesdc"
    dcOpInfo info what=oppoint where=rawfile


    Marc Heise, Jul 24, 2003
  6. Thomas Popp

    Thomas Popp Guest

    Thanks a lot, that worked!

    But I had to do it slightly different: open layout - run extraction -
    open extracted view - open LVS window - select "parasitic probe" - push
    "whole net" and select a net in the extracted layout
    No schematic view or LVS-run was needed...

    Thomas Popp, Jul 24, 2003
  7. The simples way is to run the simulation driving the input from a
    voltage source and integrate the current on the input pin.

    Two notes:
    - the precision of the simulation is very important;
    - the input cell capacitance may depend on the state of the other input
    pins (miller effect).

    Robert Szczygiel, Jul 24, 2003
  8. Thomas Popp

    Thomas Popp Guest

    Thanks for your help Marc!

    Actually I'm running the simulation of my standard cells with OCEAN
    using the simulator spectreS.

    Until now I don't mess around with the simulation netlists. I get them
    by creating a simulation schematic for a cell and starting the "Analog
    Environment". Then I create a raw and a final netlist of the whole
    simulation circuit (using the extracted netlist of the simulated
    standard cell). These netlists are then used by a OCEAN skript to
    perform the simulation.

    My question is: Is it possible to use OCEAN to tell the simulator
    __spectreS__ to compute the capacitance of an input pin of the simulated
    standard cell?

    Thomas Popp, Jul 24, 2003
  9. Thomas Popp

    Marc Heise Guest

    Hi Thomas,

    as far as I know captab did not exists in spectreS.
    The easiest would be what Robert suggestet. Let OCEAN do a simulation of a
    voltage source on your pin and do the postprocessing (integration) inside
    the same OCEAN script.

    Marc Heise, Jul 25, 2003
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