== Defining Complex Input Waveforms ==
So far you have mostly used SPICE's standard voltage sources with a few waveforms like constant, sinusoidal and pulse. In the last part of this tutorial lesson, you will use [[RF.Spice]]'s "'''Nonlinear Controlled Source'''" to synthesize more complex waveforms. For example, your input signal to the PWM modulator in the previous part was a periodic sinusoid. In this part, you will use a time-limited sinusoid with a finite duration of 8ns. You can make this waveform by multiplying the original sinusoid by a one-shot pulse of the same duration. The latter can be defined as a pulse waveform with an extremely large period:
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