Simply put, PWM is a method of digitally encoding the level of an analog signal. Through the use of high-resolution counters, the duty cycle of the square wave is modulated to encode the level of a specific analog signal. The PWM signal is still digital because, at any given moment, the full-scale DC supply is either fully (ON) or completely absent (OFF). The voltage or current source is applied to the analog load in a repetitive pulse train of ON or OFF. When it is on, it is when the DC power supply is added to the load, and when it is off, it is when the power supply is disconnected. Any analog value can be encoded using PWM as long as the bandwidth is sufficient.

By controlling analog circuits digitally, the cost and power consumption of the system can be greatly reduced. In addition, many microcontrollers and DSPs already include a PWM controller on-chip, which makes digital control easier to implement.