Pulse-width modulation

Pulse-width modulation (PWM) represents a signal by varying the fraction of each pulse period that a signal remains active. Its pulses switch between fixed levels, while their average effect changes with duty cycle.

Duty cycle: The fraction of a repeating cycle during which a signal is active. PWM changes this fraction to represent different signal values.
Class-D amplifier: An audio amplifier that uses switching output devices and filtering to reproduce sound. Many designs encode audio as PWM before filtering the switched output.
Pulse-position modulation: A modulation method that represents information through the timing position of pulses. It changes pulse timing rather than encoding the signal in pulse width.
Periodic function: A function whose values repeat after a fixed interval. PWM organizes pulses into repeating periods so duty cycle has a stable meaning.
Switching loss: Power dissipated while an electronic device transitions between conducting and nonconducting states. Increasing PWM switching frequency can improve filtering but raise these losses.
Pulse train: A sequence of pulses repeated over time. PWM encodes information by adjusting the widths of pulses in this sequence.
DC motor: An electric motor that converts direct-current electrical energy into mechanical rotation. PWM adjusts the motor's average applied voltage to control speed.
Pulse-density modulation: A method that represents signal magnitude through the local density of pulses. It varies pulse density instead of the duty cycle within each fixed period.
Square wave: A waveform that alternates between two levels with abrupt transitions. PWM commonly uses square pulses whose widths vary while their levels stay fixed.
Electromagnetic interference: Unwanted electromagnetic energy that disrupts the operation of electronic equipment. PWM's rapid edges and harmonics can generate conducted or radiated interference.

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