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A class-D amplifier is one in which the output transistors are operated as switches. When a transistor is o?, the current through it is zero. When it is on, the voltage across it is small, ideally
zero. In each case, the power dissipation is very low. This increases the e?ciency, thus requiring less power from the power supply and smaller heat sinks for the amplifier. These are important
advantages in portable battery-powered equipment. The ?°D?± in class-D is sometimes said to stand for ?°digital.?± This is not correct because the operation of the class-D amplifier is based on analog principles. There is no digital coding of the signal. Before the advent of the class-D amplifier, the standard classes were class-A, class-AB, class-B, and class-C. The ?°D?± is simply the next letter in the alphabet after ?°C.?± Indeed, the earliest work on class-D amplifiers involved vacuum tubes and
can be traced to the early 1950s. |
