In the field of audio, people have been holding the position of class A amplifier. Class A power amplifier is considered to be the freshest and most transparent, with high fidelity. However, the low efficiency and high loss of class A amplifier are the inherent problems that cannot be overcome. Although the efficiency of class B amplifier has been improved a lot, the actual efficiency is only about 50%. In small portable audio equipment such as car power amplifier, laptop audio system, and professional superpower amplifier, the efficiency is still low and unsatisfactory. Therefore, the class D amplifier with high efficiency, which is also the digital power amplifier, is being paid attention in all aspects because it conforms to the trend of the green revolution. As a result of the development of integrated circuit technology, the original discrete components used to make a very complex modulation circuit, no matter in technology or price has become a problem. In addition, with the development of digital audio technology in recent years, people have found that class D amplifier has much in common with digital audio equipment, which further shows the development advantages of the small digital power amplifier.
The small digital amplifier is a kind of amplifying mode when the amplifier is on and off. When there is no signal input, the amplifier is cut off and does not consume electricity. When it is working, the transistor is saturated by the input signal. The transistor acts as an on-off switch, connecting the power and the load directly. The ideal transistor does not consume power because it does not have a saturation voltage drop. In fact, the transistor will always have a small saturation voltage drop and consume some power. This kind of electricity consumption is only related to the characteristics of the pipe but has nothing to do with the size of signal output, so it is especially beneficial for the occasions of high power. Due to the advantages of power consumption and volume, the digital amplifier is firstly applied in the car audio system with limited energy resources and the heavy bass active speakers with high requirements. With DVD home theater, mini stereo system, set-top boxes, personal computers, LCD TV, flat panel display, and the development of consumer products such as mobile phones, especially SACD, some high, such as DVD Audio sampling frequency of the emergence of new Audio specifications, as well as from stereo sound system to the evolution of the multichannel surround system, accelerate the development of the digital power amplifier. In recent years, the price of the digital power amplifier has been decreasing, and patents related to this aspect are emerging in endlessly.