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.

For a more analog MOSFET application, consider this simple AM modulator. Figure 4 MOSFET amplitude modulator The circuit consists of an N-channel MOSFET, two resistors, and a Schottky diode. The ...