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

for . We fer to the ration as the