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Post Layout Parasitic Extraction & Simulation

Published by Team Efabless on

Prerequisites:

You authored your circuit as both:

  • an Electric schematic & icon (symbol): ~/design/YourProject/elec/yourLib.delib/yourCell.{sch,ic}
  • a magic layout: ~/design/YourProject/mag/yourCell.mag

Such that:

  • the Electric schematic cell-name matches the magic layout cell-name
  • the Electric schematic Exports (pins) match the magic layout PORTS

and you:

  • have an Electric test-bench schematic that ultimately places yourLib.delib/yourCell.ic
  • used Electric’s toolbar buttons to Sim the test-bench and view waveform results

Goal:

  • generate a post-layout RCX netlist (with parasitics) from the layout yourCell.mag
  • Sim the test-bench using the post-layout RCX netlist in place of the schematic-based subckt.

Steps:

1. ensure you define PORTS (not just text labels) in your magic layout, that match the schematic.

2. save all if you have a running magic.

3. change dir to your project’s mag dir.

% cd ~/design/YourProject/mag

4. run batch RCX extract for spice on the layout:

% magic2spi -S yourCell >m2spi.yourCell.log

Visually inspect outputs in mag/ dir (the .log and the .SPI netlist):

yourCell.mag.SPI

m2spi.yourCell.log

WARNING: Especially VERIFY the log DOES NOT end with (if so return to step#1):

info: magic2spi: no top-cell .subckt found (normal if it had no top-level ports)

5. import the RCX netlist to the dir-structure standard supported by the rcx-switcher. You must specify three args: path to the raw RCX-netlist just generated, libName, cellName.

% rcximport yourCell.mag.SPI yourLib yourCell

6. to support comparison, save copies of your test-bench raw files (pre-layout results).

7. enable the Electric Sim button (simcorners) rcx-switch behavior:

% touch ~/design/YourProject/.ef-config/view-switch.cfg

This will one-day be a real config file. Today it’s just a blunt instrument to globally (per project) turn on or off all RCX switching. Delete the file to turn it off.

8. Hit Sim button in your electric test-bench. Near top of Sim log window you should see one or more “rcxswitch: …” including a status summary. View the new post-layout waveforms; compare to pre-layout waveforms.

Challenge example:

Say your layout is named: XBG_1V23LC_V01 and intent is to switch its RCX-netlist in place of the electric schematic: XBG_1V23LC_V01.delib/XBG_1V23LC_V01.sch,

then in step-4:

% magic2spi -S XBG_1V23LC_V01 >m2spi.XBG_1V23LC_V01.log

and in step-5:

% rcximport XBG_1V23LC_V01.mag.SPI XBG_1V23LC_V01 XBG_1V23LC_V01