Amplitude Modulation, Nonlinear Modulator.

Cuthbert Nyack
One of the easiest ways to produce an AM signal is by the product modulator. Here the 2 signals (1 + m cos(wm t) and cos(wc t) are multiplied together to produe an AM signal.

Another method is by using a nonlinear circuit. One possibility is shown in the applet below where a circuit with chracteristics vo(t) = vi(t) + m/2 vi(t)2 is used.

The applet below shows how an amplitude modulated signal can be produced by a nonlinear circuit. vi(t) is in Yellow and vo(t) in Red and Green. The output has components at 0, wm, 2wm, wc - wm, wc, wc + wm, and 2wc.

The Green curve shows what happens when the frequencies other than wc - wm, wc, wc + wm are removed. In practice this would be done by a resonant circuit, coupled resonant circuits or other band pass filter.

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COPYRIGHT © 2008 Cuthbert Nyack.