APPLICATION NOTE
5
Figure 7: A simple amplitude modulator circuit
One input is the high-frequency or carrier signal, and the other input is the modulating signal.
A sinusoidal source at a frequency of 10 kHz is used to represent the carrier signal and a second source at a
frequency of 1 kHz is used to represent the modulating signal. Notice that the peak amplitude for the carrier is set
to 1 volt using the parameter VcarrierPK. The modulating index is the ratio of the peak of the modulating signal to
the peak of the carrier. Here, the index is set to 0.8 or 80% modulation. A typical broadcast AM signal includes the
carrier as well as the sidebands in the transmission. To get such a double sideband transmitted carrier signal
(DSBTC) we must bias or offset the modulating signal by a value equal to the carrier's peak voltage.
The amplitude modulated signal and the modulating signal from this simulation are shown in Figure 8
Figure 8: An amplitude modulator output signal
