Device models allow you to specify, when required, many of the parameters of the devices being simulated. In this example, model statements are used to define the silicon diodes. Electrically, the diodes serve to limit the voltage at the amplifier input to values between about (\pm)700 millivolts. The diode is simulated by first declaring the `instance' of each diode with a device statement. Instead of attempting to provide parameter information separately for both diodes, the label `1n4148' alerts the simulator that a separate model statement is included in the file that provides the necessary electrical specifications for the device (`1n4148' is the part number for the type of diode the model is meant to simulate).

The model statement that provides this information is:

.model 1n4148 D (is=2.495e-09 rs=4.755e-01 n=1.679e+00
+ tt=3.030e-09 cjo=1.700e-12 vj=1 m=1.959e-01
+ bv=1.000e+02 ibv=1.000e-04)

The model statement always begins with the string .model followed by an identifier and the model type (D for diode, NPN for NPN transistors, etc).

The optional parameters (`is', `rs', `n', …) shown in this example configure the simulator's mathematical model of the diode to match the specific behavior of a particular part (e.g. a `1n4148').