Inverter demo with magic and Skywater 130 PDK

clone this repo recusively to get the spice models from https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_fd_pr

You will also need to get your $PDK_ROOT & $PDKPATH set correct for the .magicrc file to work and load the tech file. See https://github.com/efabless/openlane/#setting-up-the-pdk-skywater-pdk for details.

To see a video of me drawing this inverter see https://www.youtube.com/watch?v=IQ_DcWT_cbc

Instructions

Start magic with the correct rcfile and load inverter.mag:

make magic

To create the spice simulation file, in the command window type:

extract
ext2spice lvs
ext2spice
quit

To get the capacitance parasitics for a more accurate simulation:

extract
ext2spice lvs
ext2spice cthresh 0
ext2spice
quit

Then in the shell type:

make sim

to run the simulation. This uses the pre.spice and post.spice files to build a complete simulation that can be run with ngspice.

The simulation is quite slow to run because there are a lot of models to include. If you want to speed things up you can comment out (add a * at the start of the line) every line from 55 onewards in sky130_fd_pr/models/sky130.lib.spice

Magic notes

gui window

useful to set grid on, snap to grid
space - change tool
box tool: left click sets one corner, right click sets next corner
x - expand (shows non expanded cells)
i - select top level cell
s - select the areas under the cursor
^D - deletes material inside the box that matches what the cursor is over
a - select what is inside the box
b - prints out size of the box
middle click any material or palette boxes on the left sets the box to that material

useful command window commands

what - what is selected
ext - extract circuit from the design
ext2spice lvs ; ext2spice subcircuit top on; ext2spice - setup ext2spice with the lvs settings (compatible with sky130), set export inside a subcircuit, then create the spice file to be used for simulation
label NAME - create a label attached to whatever is selected
measure - measures the box
move up 10 - moves the selection up by 10
copy up 10 - copies selection up by 10

Attribution