PWM "Intersection"
It's classic. It involves comparing the modulation (the signal to synthesize) a generally triangular carrier. The output is 1 if the module is larger than the carrier, 0 otherwise; the output signal therefore changes state at each intersection of the modulating carrier.
This method lends itself well to achieve analog is just a triangle generator and a comparator. There are many dedicated integrated circuits.
We can classify subtypes of several ways:
• Analog or digital sampled by the comparator module and time are continuous or discrete;
• To focus bearing triangular or sawtooth (left or right);
• Asynchronous or synchronous, as the modulating and carrier frequency exactly are multiple or not.