SPICE-Simulation using LTspice IV

9.3. Parametric Sweep
If you have a look at “LTspice / Dot Commands“ in the online help, then you will find a lot of commands and
capabilities.
Let us test the SPICE-command
.step
This is important because with „step“ you can automatically vary the value of a part or a voltage and repeat the
simulation.
Let’s take the circuit of the last section and vary the upper resistor R1 in the base voltage divider in 5 steps from
10k to 15k. This will enable you to get the optimum operating point.
Note:
a) The peak value of the input voltage is now 0.3V
b) The value of R1 is replaced by the variable {Rx}
c) With the spice directive .step param Rx 10k 15k 1k the value of Rx is
increased from 10k to 15k in steps of 1k.
Now press the simulation button ( the “running guy”). The simulation will run, but you don’t see any results. So
move your cursor to the collector of the transistor Q2 and click.
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