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Pulse-width modulation is a way to represent data over a communications channel. With pulse-width modulation, the value of a sample of data is represented by the length of a pulse.
Pulses of various lengths (the information itself) will be sent at regular intervals (the carrier frequency of the modulation).
_ _ _ _ _ _ _ _
| | | | | | | | | | | | | | | |
Clock | | | | | | | | | | | | | | | |
__| |____| |____| |____| |____| |____| |____| |____| |____
_ __ ____ ____ _
Data | | | | | | | | | |
| | | | | | | | | |
_________| |____| |___| |________| |_| |___________
Data 0 1 2 4 0 4 1 0
The clock signal is not necessary as the leading edge of the data signal can be used as the clock if a small offset is added to the data value in order to avoid the lack of a pulse for zero values.
PWM is also used to vary the total amount of power delivered to a load without resistive waste. An RC filter can be used to smooth the pulse train into a steady analog voltage. This method is commonly used in DC motor speed control.
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