In the field of sound, people have always adhered to the position of class A power amplifier. It is considered that class A power amplifier has the freshest sound and class D power chip is transparent and high fidelity. However, the low efficiency and high loss of class A power amplifier are its inherent disadvantages that cannot be overcome. Although the efficiency of Class B power amplifier has improved a lot, the actual efficiency is only about 50%. In small portable audio equipment such as car power amplifier, notebook computer audio system and professional super power amplifier, the efficiency is still unsatisfactory. Therefore, the class D amplifier with high efficiency is attracting attention from all sides, because it conforms to the trend of the green revolution. Due to the development of integrated circuit technology, the complex modulation circuit composed of discrete components is no longer a problem in technology or price. Moreover, with the development of digital audio technology in recent years, people find that class D power amplifier and digital audio have a lot in common, which further illustrates the development advantages of class D power amplifier. Class d power amplifier is an amplification mode, in which the amplifier elements are in the switching state. When there is no signal input, the amplifier is in a closed state and does not consume power. When working, the transistor is saturated by the input signal, and the transistor is equivalent to a conducting switch, which directly connects the power supply with the load. An ideal transistor consumes no power because there is no saturation voltage drop. In fact, transistors always have a small saturation voltage drop, which consumes some electric energy. This power consumption is only related to the characteristics of the lamp, and has nothing to do with the size of the signal output, so it is especially beneficial to ultra-high power occasions. Ideally, the efficiency of Class D amplifier is 100%, Class B amplifier is 78.5%, and Class A amplifier is only 50% or 25% (depending on the load mode). Class D power amplifier actually has switching function, which was only used in the switch control circuit of relays, motors and other actuators in the early days. However, with the development of digital audio technology, the switching function (that is, the function of generating digital signals) becomes more and more smooth. In the 1960s, designers began to study the audio amplification technology of Class D power amplifiers, and in the 1970s, Bose Company began to produce Class D automotive power amplifiers. On the one hand, the battery power supply for automobiles needs higher efficiency, on the other hand, the space is too small to accommodate the power amplifier with large heat dissipation plate structure, and both of them hope to have an efficient power amplifier similar to Class D to amplify new audio signals. One of the key steps is the modulation of audio signal.