I needed to make an amplitude modulator as part of a signal generator design. I took the approach of using an RCA type CA3004 as a variable transconductance amplifier. It worked very nicely. Figure 1 ...

Simple long-tailed pairs had a long history prior to the advent of integrated circuits, starting in the 1930s with tube circuits and being recreated with transistors as those devices were invented.

See MODULATION for a sound example. Amplitude modulation spectrum of two sine waves, carrier C and modulator M, showing the addition of a pair of sidebands, C + M and C - M, around the carrier. The ...

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.