You can download the latest version of ngspice from the official ngspice site. You can also download the version 43 version 43 I am using. It is a good idea to also download the user manual from the same site.
You can now install the ngspice folder named Spice64 where you want. I created a NGSpice folder in the C:\Program Files\ folder and copied the Spice64 folder in it. So for my installation, the path to the ngspice binary is C:\Program Files\NGSpice\Spice64\bin. Of course you can choose any other installation location.
Once you have installed (copied) ngspice, you need to check whther the PSP 103.6 osdi file that contains the PSP MOSFET model that is used for the simulations is already installed. Go to the folder <your ngspice installation path>\Spice64\lib\ngspice\ where you should see the psp103_nqs.osdi file and other osdi files. If it is not included, you can copy the psp103_nqs.osdi file from the PSP Verilog-A directory and save it to the folder your ngspice installation path\Spice64\lib\ngspice.
You then need to modify the spinit file of ngspice that is in the follwoing folder <your ngspice installation path>\Spice64\share\ngspice\scripts. You can replace it by the spinit file found in the ngspice directory. This file is run each time ngspice is started. It will load the psp103_nqs.osdi file for running simulations with the PSP compact model. Note that the other osdi models have been disabled by adding the star at the beginning of the line. If you want to use of these models you just remove the start on the corresponding line.
Before running ngspice, you still need to add a few variables to the Windows Environment variables. In order to do this in Windows 10 or Windows 11, open Settings>Sytem>About. On the right panel click Advanced system settings. You will see this dialog box
Click in the Environment Variables... button which open this dialog box
In order to tell ngspice where to find the osdi model library, you then need to create a new System variable:
Variable name: NGSPICE_OSDI_DIR
Variable value:\Spice64\lib\ngspice\
as shown below:
In order to tell ngspice where to find the spinit file, you need to create the following System variable:
Variable name: SPICE_SCRIPTS
Variable value: \Spice64\share\ngspice\scripts\
as shown below:
You are now all set to run the examples.
Enjoy!