Erik Diez (Keysight/Agilent Technologies) wrote a
great article in Electronic Design describing the fundamentals of signal generators - indispensable tools for developing and testing
electronic devices and systems.
Being from Keysight, of course they lay claim
to the beginnings of the electronic test-and-measurement industry: the model
200A audio oscillator for the Walt Disney Company—in 1940, used for the movie
Today, typical applications include RF/IF signal generation and
LO substitution, as well as radar, GPS, and avionics signal simulation.
In modern wireless communications systems, signal generators supporting a range
of digital-modulation formats are commonly used to test digital receivers and
transmitters against increasingly complex requirements.