The basic circuit of the "digital power amplifier" is the long-existing Class D amplifier (called Class D amplifier in China). Previously, due to price and technical reasons, such amplifying circuits were only used in laboratories or high-priced test instruments. In recent years, technological developments have integrated the components of digital power amplifiers into one or two chips, and the price has been falling. Theoretically, the efficiency of Class D amplifiers can reach 100%. However, the ideal switching element has not been found so far, and it is inevitable that some power loss will occur, and if the device used is poor, the loss will be greater. But in any case, its amplification efficiency is still more than 90%.

    Due to the advantages of power consumption and volume, digital power amplifiers are first applied in car audio with limited energy and heavy bass active speakers with high requirements. With the rapid development of consumer products such as DVD home theater, mini sound system, set-top box, personal computer, LCD TV, flat panel display and mobile phone, especially the emergence of some new audio source specifications with high sampling frequency such as SACD and DVDAudio, and the evolution of sound system from stereo to multi-channel surround system, Have accelerated the development of digital amplifiers. In recent years, the price of digital power amplifiers has been declining, and patents in this regard have emerged in endlessly.

    An amplifier that uses low-frequency audio signals to modulate a pulse width of a fixed high-frequency frequency is known as a class D amplifier and some people are called digital audio amplifiers, his biggest feature is that the efficiency is particularly high (in theory can reach 100%, in practice more than 85%), the use of very small electronic devices can produce a large power audio amplifier.

    For low-power, 1W-3W power amplifiers, the power efficiency of Class AB power amplifiers and Class D power amplifiers is about AB=15% and D=75% respectively under the condition of the same playback content. In the case of playing 1W music, the Class AB power amplifier needs to consume 6.7W of power, but the Class D power amplifier consumes only 1.33W under the same playback conditions. Therefore, the use of a Class D power amplifier can extend the battery life by up to 5 times (6.7W/1.33W). Low power usage In addition to mobile phones, DVD, MP3 and PMP there are some popular products such as iPods, mobile phones, and digital photo frames. In the case of medium power, that is, 10W-30W power amplifier, the power efficiency of Class AB power amplifier and Class D power amplifier is AB= 25% and D=80% respectively when the same playback content is mainly voice.

    In the case of 10W speech, the Class AB power amplifier needs to lose 40W of power, but the Class D power amplifier only loses 12.5Watts of power under the same conditions. Therefore, the use of Class D power amplifier can reduce the cost of the power supply by nearly 3 times (40W/12.5W), and the 2.5W heat generated by the Class D power amplifier can be handled by the general power package and PCB design without additional heat sink. In the case of high power output, that is, 100W-200W Class D digital power amplifier will also have a place in the car audio, under this high power class D power amplifier is still inevitable to use heat sink, but the heat dissipation area and heat dissipation than class AB power amplifier required to be smaller, due to high efficiency reasons, Class D power amplifier can be used for a long time without starting the car engine without consuming too much battery power, Class D power amplifier has become the main application product of car audio.

    Manufacturers do not use sound content as a standard when calculating power, but use traditional sine wave signals as input. For example, the power efficiency of Class AB power amplifiers and Class D power amplifiers is about 45% and 80% respectively for sine wave signals. If you use 15W×2 to calculate the total supply power of Class D power amplifier is about 30W/80%=37.5W, and the total supply power of class AB power amplifier is about 30W/45%= 66.7W, so the use of class D power amplifier can save nearly 30W power. Since the power supply of the power amplifier is provided by the power supply device, the cost of the power supply device of the Class D power amplifier will be greatly reduced. At the same time, the cost of the heat sink and power amplifier heat sink of the power supply device and the cost of the circuit plate space have been greatly reduced.

    The overload capacity of digital power amplifier circuit is much higher than that of analog power amplifier. The analog power amplifier circuit is divided into class A, Class B or class AB power amplifier circuit, and the power amplifier tube works in the linear region during normal operation; When the overload, the power amplifier works in the saturated area, harmonic distortion occurs, the degree of distortion increases exponentially, and the sound quality deteriorates rapidly. The digital power amplifier has been in the saturation region and the cut-off region when the power amplifier is amplified, and the distortion degree will not increase rapidly as long as the amplifier tube is not damaged.

    Comparison of overload distortion degree between all digital power amplifier and ordinary power amplifier

    Because the digital power amplifier uses a switching amplifier circuit, the efficiency is extremely high, up to 75%~90% (the analog power amplifier efficiency is only 30%~50%), and there is basically no heat at work. Therefore, it does not simulate the static current consumption of power amplifier, all energy is almost reserved for audio output, coupled with no analog amplification before and after, no negative feedback check, so it has better "power" characteristics, transient response is good, "explosion sense" is very strong.

    Analog Class B power amplifier in zero-cross distortion, which is due to the nonlinear characteristics of the transistor in the small current caused by the distortion at the positive and negative intersection of the output waveform (small signal transistor will work in the cut-off zone, no current through, resulting in serious distortion of the output). The digital power amplifier only works in the switching state and does not produce crossover distortion.

    The analog power amplifier has the mismatch distortion of the output waveform caused by the inconsistent characteristics of the push-pull pair tube, so the requirements of the power amplifier tube are very strict when designing the push-pull amplifier circuit. The digital power amplifier has no special requirements for the pairing of the switch tube, and basically does not require strict selection to be used.

    Due to the large internal resistance of the amplifier tube in the analog power amplifier, the working state of the analog power amplifier circuit will be affected by the size of the load (speaker) when matching speakers with different resistance values. The internal resistance of the digital power amplifier does not exceed 0.2Ω (the internal resistance of the switch tube plus the internal resistance of the filter), and the resistance value (4~8Ω) relative to the load (speaker) is completely negligible, so there is no matching problem with the speaker.

    Almost all the analog power amplifier uses negative feedback circuit to ensure its electroacoustic index, in the negative feedback circuit, in order to suppress parasitic oscillation, the phase compensation circuit is used, which will produce transient intermodulation distortion. Digital amplifiers do not use any analog amplification feedback circuit in power conversion, thus avoiding transient intermodulation distortion.

    For analog amplifiers, there is generally a phase difference between the output signal and the input signal, and the phase distortion is different when the output power is different. The digital power amplifier uses digital signal amplification, so that the phase of the output signal and the input signal are completely consistent, and the phase shift is zero, so the sound and image positioning is accurate.

    Digital power amplifiers can gain high power by simply replacing the switching amplifier module. The high power switch amplifier module has low cost and broad development prospect in the professional field.

    The analog power amplifier has the debugging problem of various working points, which is not conducive to mass production. Most of the digital amplifiers are digital circuits, which generally can work normally without debugging, and are especially suitable for large-scale production.

     The so-called "digital" power amplifier only uses digital signal processing on the pre-stage, after the input of analog audio signal or digital audio signal, the existing digital audio processing integrated circuit is used to achieve some functions such as sound field processing, digital delay, reverberation and so on, and finally audio amplification through the analog power amplifier module. The interface of each module is analog, and the digital power amplifier is different.

    Although the current integrated circuit manufacturers have introduced digital sound field processing, digital karaoke and digital Dolby decoding integrated circuits. However, because most of the current power amplifier can only receive analog audio signals, so the interface of the integrated circuit is mostly analog, which requires repeated analog/digital, digital/analog conversion, which will introduce quantization noise, so that the sound quality deteriorates.

    In addition to the interface for the speaker (this is because the speaker can only accept analog audio signals), the audio signal is processed in the way of digital signals inside the amplifier (including power amplification); For analog audio signals, they must be converted into digital signals before they can be processed.

    The introduction of digital amplifiers in an era where digital audio is already available will likely have a significant impact on the development of audio technology.