A frequency multiplier is an electronic circuit that creates a (typically integer) harmonic of its input frequency – for example it could be used to double a 200 Hz input to 400 Hz at the output. Frequency multipliers use a nonlinear circuit to severely distort the input signal, before applying a band-pass filter to only provide the desired multiple of the input frequency. A frequency divider does the inverse of a frequency multiplier, in that it divides an input frequency to a lower rate.
Frequency multipliers and dividers are used in both digital and analog applications.
Frequency multipliers are often seen as a more economical way to create high-frequency signals from low-frequency inputs, which are easier to generate. Common applications include PLL frequency synthesisers, signal generators and communications circuits.
Frequency dividers can be used for applications including satellite communications, fibre optics and point-to-multipoint radios, as these require very high frequencies to operate effectively.