In telecommunications, frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency. In analog applications, the difference between the instantaneous and the base frequency of the carrier is directly proportional to the instantaneous value of the input signal. Digital data can be sent by shifting the carrier's frequency among a set of discrete values, a technique known as frequency-shift keying.
Frequency modulation can be regarded as phase modulation where the carrier phase modulation is the time integral of the FM modulating signal. Let us study more about the frequency modulation in this section.