MrWalkman
Headphoneus Supremus
yes but what is the problem he is experiencing, I still don't understand it ?
It is a real problem - not for everyone, it's true, but it exists.
Before we talk about PWM, we need to explain the basics about signal types. There are two basic kinds of signal types — Analog and Digital. Analog signal types have degrees of intensity, between 0% (off) and 100% (maximum), allowing for a range of accuracy when determining something like screen brightness or fan speed. Digital signal types, on the other hand, have no degrees of intensity; they simply have an off or on state. This means something like brightness control is impossible on its own, because in digital terms, the backlight is either on or off.
Digital signal controllers, however, are cheaper, smaller, more power efficient, and simpler to implement than analog controls. In order to take advantage of the benefits of digital signal controllers while retaining (and even surpassing) analog functionality, PWM is used.
PWM is a very rapid frequency of on/off states of the digital signal to achieve a result similar to what could be achieved on a plain Analog signal. If you wanted 70% screen brightness for example, you would simply need to keep the digital signal on for 70% of the time and off for 30% of the time your screen was turned on. This is done rapidly, with the frequency measured in Hertz (Hz), or number of times per second. The faster the frequency, the less noticeable the off states become, until the resulting effect is indistinguishable from what an analog signal would produce.
The idea is that some people can perceive the off and on turning of the display. Imagine watching a quickly flashing light. Depending on the person, it may cause headaches, or even seizures for persons with epilepsy for example. It's not the case with PWM, as the frequency is higher, but sometimes it's not high enough, and people can perceive that "flashing".