6. Layout Extraction

6-1.Back Annotation For Post-Layout Simulation in Accusim & Layout Extraction for HSPICE netlist

After you make sure the layout complies with the design rules (DRC) and matches your schematic (LVS), you may want to "run" your layout in an analog simulator to see if it works, i.e. to run post-layout simulation. The parasitic devices which include net capacitance, net resistance and coupled capacitance create delays in your circuit. They can be back annotated to your schematic for a more realistic evaluation of circuit performance. To do this, follow the procedure given below.

From 'IC Palettes', select "ICextract(M)"

Select 'Load Rules' to load the rules file. You may enter the rules filename or use Navigator to choose the rules file that you have created.

In this example, enter "$MGC_CMOSN_LIB/physical_lib/cmosn.rules" for the rules file name then click on 'OK'.

Open your logic (i.e. schematic) by selecting

Logic -> open

Extract HSPICE netlist only.

Select 'Yes' for Write Database
Select 'Netlist' from 'ICextract(M)' palette.
A 'Write Mask Netlist' dialog box will appear. Enter filename you want to be saved for 'name' box. Select 'Yes' for "Specify Schematic Source". This will adopt the net/port name you gave in the schematic into netlist.
Enter the schematic name for the "Source Name" field. Click 'OK' to generate an HSPICE netlist from your layout. You can use any text editor to edit this netlist file.

Select 'Yes' for BackAnnotate Device Properties.Specify the name you want to save it as. e.g.. inverter.ba

Figure 6-1. Write Mask Netlist dialog box

Extract HSPICE netlist with lumped capacitance.

Select 'Lumped' from 'ICextract(M)' palette. A 'Extract Mask Lumped Parameters' dialog box will appear. Click on 'Yes' for Netlist, the dialog box will be extended.

Figure 6-2. Extract Mask Lumped Parameters dialog box

Enter filename you want to be saved for 'Netlist Name' box. Click on 'Yes' for 'Use Lumped Cap?'. Select 'Yes' for "Specify Schematic Source". This will adopt the net/port name you gave in the schematic into netlist. Enter schematic name for the "Source Name" field.
For backannotation select the BackAnnotate option and specify the name you want it to be stored as in the box below. You can also select other options under the backannotation depending on the requirement.Then click 'OK'.

A HSPICE netlist file with parasitic capacitance will be generated from your layout. You can use any text editor to edit this netlist file.

NOTE

Run your schematic in Accusim again, you will see the difference in schematic as well as the simulation results. Please refer to Accusim II, Sec 5. Simulation In Accusim tutorial for analog simulation procedure

Extract HSPICE netlist with distributed capacitance and resistance.

Select 'Distributed' from 'ICextract(M)' palette. An 'Extract Mask Distributed Parameters' dialog box will appear. Click on 'Yes' for Netlist, the dialog box will be extended.

Figure 6-3. Extract Mask Distributed Parameters dialog box

Enter the filename you want the netlist to be saved under in the 'Netlist Name' box. Click on 'Yes' for 'Reduction,' to model net resistance . Select 'Yes' for "Specify Schematic Source". This will adopt the net/port name you gave in the schematic into the netlist. Enter the schematic name for the "Source Name" field.
For backannotation select the BackAnnotate option and specify the name you want it to be stored as in the box below. You can also select the other options under the backannotation depending on the requirement.Then click 'OK'.

A HSPICE netlist file with parasitic capacitances and resistances will be generated from your layout. You can use any text editor to edit this netlist file and run HSPICE simulation.

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