Characterise the inductor (optional)
We will now use OpenEMS to characterise the inductor drew in Layout to verify its inductance. It is quite important for a LNA to ensure we use the right value for our inductors. However this step can be long (several hours, even on powerful computers/servers), so if you don’t plan to manufacture your design and/or use the exact same value, you can skip this part.
Generate GDS polygons
We need to convert our previously generated GDS into a format compatible with OpenEMS. Here we will use python, but the IHP Open PDK also offers some script to generate a Octave/Matlab code instead of python.
Move to the ~/microelectronics/PDK/IHP/IHP-Open-PDK/ihp-sg13g2/libs.tech/openems/import_GDSII and run:
python3 gds2pythonpoly.py ~/microelectronics/projects/test_inductor.gds
This will generate a file test_inductor_polygons.py that contains the geometry of our inductor in python format for
the OpenEMS flow. Move it to your projects folder:
mv ~/microelectronics/PDK/IHP/IHP-Open-PDK/ihp-sg13g2/libs.tech/openems/import_GDSII/test_inductor_polygons.py ~/microelectronics/projects/
Preparing simulation
Now create a new “scripts” folder in tools :
mkdir -p ~/microelectronics/tools/scripts
And download the scripts ihp_openems_simu.py and ihp_openems_mat_const.py in that directory:
wget ... TODO from gist or something... -O ~/microelectronics/tools/scripts/ihp_openems_simu.py
wget ... TODO from gist or something... -O ~/microelectronics/tools/scripts/ihp_openems_mat_const.py
These scripts allow you to simulate a gds with OpenEMS using IHP’s materials parameters. The only things you have to
specify with this script, the python file of the input layout (in our case it will be test_inductor_polygons.py)
and the simulation port. You can run the simulation with the bare minimum like this:
Starting 1-port simulation
To run the simulation run the downloaded script like this:
python3 ihp_openems_simu.py -P tm1:-14,0,14,10:x:50 test_inductor_polygons.py
-P like this:Material : Lower Left X, Lower Left Y, Upper Right X, Upper Right Y : Direction : Impedancetm1.(-14, 0) and (14, 10), you only
have to adapt this on your side.x axis and we use a 50 Ohm port.test_inductor_polygons.py is the path to the file we want to simulate.If you want to know more about the script and its parameters you can run:
python3 ihp_openems_simu.py --help
By default, the simulation will use a 1um resolution mesh, and simulate form 0Hz to 30GHz.
After you ran the command, you will see a window will open with a preview of your layout, you will also see the port. This will allow you to verify it is well placed. You should have something like this:
Then you can close this window, which will start the simulation. If you realised your port (dark green box on the image
above) was wrongly placed, you can cancel the simulation with the keyboard keys Ctrl + C. If you only want to
see the preview without running the simulation, you can add the parameter -v to the previous command.
Once the simulation has started, it will certainly take several hours depending on the parameters you set, the complexity of your layout and the performance of your computer. At the end of the simulation you will have something like this:
[@ 18h56m29s] Timestep: 6918093 || Speed: 33.3 MC/s (9.807e-03 s/TS) || Energy: ~6.77e-21 (-38.58dB)
[@ 19h06m08s] Timestep: 6977222 || Speed: 33.3 MC/s (9.801e-03 s/TS) || Energy: ~2.28e-21 (-43.31dB)
[@ 19h15m48s] Timestep: 7036351 || Speed: 33.3 MC/s (9.805e-03 s/TS) || Energy: ~7.24e-23 (-58.29dB)
Time for 7036351 iterations with 326430.00 cells : 69348.59 sec
Speed: 33.12 MCells/s
Visualising results
To open the results you can simply use the same command as before but with adding the parameter -p:
python3 ihp_openems_simu.py -P tm1:-14,0,14,10:x:50 test_inductor_polygons.py -p
In your terminal you will have something like this:
Frequency [GHz]: 2.45
Series L [nH] : 3.8582205280749458
Series R [Ohm]: 9.532990303191587
Q factor : 6.230226688478917
----------------
L_DC [nH] : 3.8024062009152657
R_DC [Ohm]: 8.91215940806006
Peak Q : 6.924194376059975
And 3 windows will open, with graphicals results of your simulation for the Q-factor, the inductance and the resistor of your inductor. You should have something like this:
With the text result in the terminal, we can see that at 2.45 GHz, our inductor as a value of 3.86nH.
The results are taken from the directory sim_out/test_inductor_polygons. If you ran the previous command with -p
as explained, you will find a .s1p file in this directory. This file will then be used in Qucs-S (or any other
software) to simulate with the “real” inductor behaviour.