Despite the need for an IC, this ubiquitous interface between the modulator and audio-video signals has not been reduced to an integrated circuit. The major reasons for that deficiency are the ...

Fig 1. Density addition and subtraction can easily separate these audio channels before digitalization. Fig 2. Density multiplication can easily be used to multiply these two inputs in several ...

If we replace the potentiometer VR1 with an AC signal plus DC bias signal in any of the previous Figures 3 to 17, the voltage controlled attenuators can become an amplitude modulator circuit instead.