The simulation library allows you to explore different designs and understand the simulation setups, which will be covered in detail throughout the course. To get started, try opening dc_lv_nmos by selecting the instance and pressing e. This will open the schematic view.
From here, navigate to the "netlist" button in the top-right corner, then press "simulate." Your first schematic simulation in Xschem will now be complete. View the results by left-clicking the green arrow while holding down Ctrl. The output should look like this:
Analog design requires a solid foundation in analog electronics to ensure high-performance, robust designs. In this course, we will focus on the gm/Id methodology rather than traditional small-signal calculations using square-law models. This method uses model parameters to generate lookup tables, enabling a more data-driven approach to design. If you're interested in understanding the circuit design procedures in greater detail, each module includes Jupyter Notebook scripts as references for more advanced IC design using open-source tools.
Switch to the "Ngspice" branch and clone the repository to a destination of your choice. Follow the installation instructions in the README. To generate the lookup table, create a configuration file specifying parameters. Below is a sample configuration file to sweep the low-voltage devices, sg13_lv_nmos and sg13_lv_pmos, with relevant parameters:
This command will generate a .pkl file that serves as the lookup table. To test the table, navigate to the scripting folder in this module and open gmid_commonsource.ipynb.
Note: Ensure the paths to sg13g2_nmos_lv and sg13g2_pmos_lv are correctly referenced in your config file, and modify the LUT path in the script to point to the location of your lookup tables.
## Verifying gm/Id Design in Xschem (Optional)
To verify the design created using the lookup tables, start by identifying key parameters to validate, such as DC gain and the first pole. This requires creating a frequency analysis simulation to capture both characteristics. Begin by creating a new schematic in some specified folder:
the first thing we want to do is the instanciate our mosfets. In this example we make a current mirror for biasing our output transistor to the right operation. Therefore we will need to instanciate two MOSFETS. This is done by navigating to the insert symbol botton, with a nandgate as its icon. Or you can press shift+i. Here you want to click the IHP open pdk path, and click on "sg13g2_pr". Here you should select the "sg13_lv_nmos.sym", and press OK. Now you will place it and duplicate it by pressing it and clicking "c". Now you can press shift+f while toggeling the instance for flipping it and place it in a gate to gate configuration as shown in the image:
select each instance and press Q to change the widht and the length to the parameters found in the gmid script.
Now you should conncect the bulk of the devices to the sources with a wire, by pressing "w" and dragging the wire to its location. After this navigate to the symbol library, again by pressing and instanciate the following items:
