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## What is Pulse Width Modulation?

Pulse width modulation or PWM is a standard way by which a digital device can generate an analog voltage. This section discusses how you can use the MicroStamp11 to generate a PWM signal that can be interfaced to a simple capacitive circuit and thereby generate an analog voltage.

Let's define a signal as a function that maps time onto some real number. Consider, for instance, a two-terminal electronic device. The voltage over this device at time is denoted as . We can think of as mapping the time to the voltage .

We say a signal, is periodic if there exists a positive time such that for all . In other words, at any moment, , in time, the value of ( ) will always be repeated at regular time intervals in the future. We refer to as the period of the signal. If is the smallest such positive number such that , then we refer to as the signal's fundamental period. If is the period of a periodic signal , we often refer to as being -periodic.

A pulse width modulated signal is a -periodic signal, , where there exists a time such that and such that (1)

for . We fer to the ration as the duty cycle of the signal. We usually represent the duty cycle as a percentage. Equation 1 defines the values that takes over a single period, . Since is -periodic, we know that the pattern characterized in equation 1 will repeat itself at regular intervals of duration . Figure 33 shows a pulse-width modulated signal whose duty cycle is .    Next: How to use a Up: Output Compare Interrupts Previous: Declaring the ISR's Interrupt
Bill Goodwine 2002-09-29