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LTSPICE Tutorial

The first step in running a SPICE simulation with LTSPICE is downloading and installing LTSPICE from the Linear Technology website. The link is as follows:

After downloading and installing the software, to simulate a circuit, start LTSPICE and create a new shcematic using File -> New Schematic. This schematic is named as a draft and saved to the default LTSPICE directory, so the next step should be saving this schematic in a directory that contains your model library file. Use File -> Save As for this; if you use File -> Save, the schematic file will be saved at LTSPICE software directory.

After saving your empty schematic to the directory which also contains your model file, you should tell the schematic and thus, the netlist it'll generate, to reference that model file. To do this, you should press 'S', or choose Edit -> SPICE Directive. Make sure that the radiobox "SPICE Directive" is highlighted, and insert the spice directive to reference your library here; which, for the example library, is:

.lib 'classprocess.lib' TT

Obviously, the 'classprocess.lib' part refers to the filename of the library file (which should be saved in the SAME directory as the schematic file for this to work); whereas the TT part refers to the specific process corner you'd like to run the simulation with. (You probably do not need to be bothered by this for the time being.)

The next immediate step you should take is disabling the default model libraries LTSPICE has; otherwise, it'll just use its own libraries and parameters instead of the device parameters you've provided. This is accomplished by clearing the following checkboxes:

Tools -> Control Panel -> Netlist Options -> Semiconductor Models -> Default Devices and Default Libraries

Finally, go to:

Tools -> Control Panel -> SPICE

and set the Reltol parameter to 1e-6. Now you're ready to run a respectable analog simulation in LTSPICE using BSIM3v3 device models.

Populate your circuit using Edit -> Component or 'F2', connect your components using Edit -> Draw Wire or 'F3', add wire labels using Edit -> Label Net or 'F4'. Do not forget to place a ground to your circuit using Edit -> Place Ground or 'G'.

Happy simulating!

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