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Oftentimes in EE classes we learn about AC analysis and phasors and other stuff heavily based on analog signals. I also know that many digital applications approximate analog signals using PWM. But does everything we learn regarding analog signals still apply to PWM signals? For example, I can see why the integral of a PWM and analog signal would be (almost) the same, but wouldn't the derivatives be drastically different?

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  • \$\begingroup\$ I think you may be confusing a few different concepts here. PWM stands for Pulse Width Modulation where the width being modulated is that of a square wave. An analog signal is anything not digital. There is a bit of grey area here, however, since even a DC signal is an analog signal that does not change and has zero slope. Some things very obviously fall into the analog category (like sinusoids), while others are may be categorized either way depending on who is doing it and their opinion. \$\endgroup\$ – sherrellbc Apr 3 '15 at 23:36
  • \$\begingroup\$ I am relatively new to EE, so thanks for the clarification. However, I've read some articles like this that suggest that "PWM is a trick microcontrollers can use to make a digital signal appear to be analog." \$\endgroup\$ – woojoo666 Apr 3 '15 at 23:49
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[General remark: Treat hobby-grade sources like SparkFun with a pinch of salt. Their objective is to make things easy, fun, exciting, practical without getting bored with integrals and derivatives. As a result, you get loose statements occasionally.]

In some books, PWM is called a pseudo-analog signal. It has only high and low voltage level, but timing is continuous. Timing is either truly continuous, or it has high enough digital resolution where it can be considered continuous for practical intents and purposes. When PWM is converted to an actual analog signal, that's always done with a low-pass filter of some sort. Here's are some examples:

  • So called "poor man's DAC", which consists of a PWM output from a microcntroller followed by a low-pass filter.
  • Buck converter
  • Class D amplifier
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