What is the name of the type of modulation in which the modulating signal varies the duration of the transmitted pulse?

The type of modulation in which the modulating signal varies the duration of the transmitted pulse is known as pulse-width modulation (PWM). In PWM, the width of the pulse changes in accordance with the amplitude of the modulating signal while the frequency remains constant. This technique is widely used in various applications, including lighting control, motor control, and audio signal processing, because it can efficiently convey information while allowing for easy implementation in digital circuits.

In contrast, frequency modulation involves varying the frequency of the carrier wave according to the modulating signal's amplitude, not the pulse duration. Amplitude modulation changes the amplitude of the carrier wave, which is also unrelated to pulse width. Phase modulation, on the other hand, alters the phase of the carrier signal to encode information, rather than changing the length of the pulses. Understanding these distinctions helps clarify why pulse-width modulation is the accurate identification for this modulation method.