15.9 P RODUCTION OF A MPLITUDE M ODULATED W AVE

. P RODUCTION OF A MPLITUDE M ODULATED W AVE Amplitude modulation can be produced by a variety of methods. A conceptually simple method is shown in the block diagram of Fig. . . FIGURE . Block diagram of a simple modulator for obtaining an AM signal. Here the modulating signal A m sin , m t is added to the carrier signal A c sin , c t to produce the signal x ( t ). This signal x ( t ) = A m sin , m t + A c sin , c t is passed through a square law device which is a non-linear device which produces an output y ( t ) = B x ( t ) + Cx ( t ) ( . ) where B and C are constants. Thus, y ( t )= BA m sin , m t + BA c sin , c t sin sin sin sin c c c c C A t A t A A t t  ( . ) = BA m sin , m t + BA c sin , c t – cos2 – cos2 c c c C A C A C A A t t + CA m A c cos ( , c – , m ) t – CA m A c cos ( , c + , m ) t ( . ) where the trigonometric relations sin A = ( – cos2 A )/ and the relation for sin A sin B mentioned earlier are used.