What is a digital power amplifier? What is its circuit principle?

                    What is a digital power amplifier? What is its circuit principle?

Digital amplifiers are a product of the digital age. The conversion process of digital 0 and 1 signals of digital power amplifier is simply understood as it belongs to the category of class D power amplifier.

In fact, the class D power amplifier only adopts the amplification principle similar to the pulse width modulation of the switching power supply. If it is a professional-grade digital power amplifier, it more refers to the function of DSP (an abbreviation of English words; a technical discipline that analyzes, transforms, filters, detects, modulates, demodulates, and other fast algorithms for signals in digital form) functions. Power amplifier, DSP power amplifier refers to a power amplifier that uses a DSP chip to optimize and manage audio parameters through digital signal processing algorithms. It is a technology that converts a two-channel stereo signal into a multi-channel surround sound signal.

Class D power amplifier is an amplification mode in which the amplifying element is in a switching state. When there is no signal input, the amplifier is in the cut-off state and does not consume power. When working, the input signal often makes the transistor enter a saturated state, and the transistor is equivalent to a switch that is turned on, directly connecting the power supply and the load. Ideal transistors do not consume power because they have no saturation voltage drop. In fact, transistors always have a small saturation voltage drop and consume part of the power. This kind of power consumption is only related to the characteristics of the tube and has nothing to do with the size of the signal output, so it is especially beneficial to the occasion of super high power. Under ideal conditions, the efficiency of Class D power amplifier is 100%, the efficiency of Class B power amplifier is 78.5%, and the efficiency of Class A power amplifier is only 50% or 25% (depending on the load mode). Generally speaking, the rated output of Class D power amplifier is The power is sufficient and the rated output of Class AB power is only about 70%. Class D power amplifiers care about power, while Class AB power amplifiers only care about general quality, and subwoofers must care about sufficient output in power.

The basic working principle of digital power amplifier

Block Diagram of Digital Power Amplifier

Digital power amplifier is generally composed of several parts such as pulse generator, PWM circuit, switching amplifier and demodulator. The pulse generator generates a square wave signal with a duty cycle of 50%. The audio signal is input from the Vin terminal, and the pulse width modulation is performed on the square wave signal output by the pulse generator, so that the pulse width is proportional to the amplitude of the input audio signal. width modulated pulse signal. After the signal is amplified by the switching amplifier (the power tube works in the switch state), and then demodulated by the low-pass filter, the speaker can be driven to work. This is the basic working principle of the digital power amplifier. The actual digital power amplifier circuit is more complicated than this, but now there are many high-quality and cheap digital power amplifier ICs on the market. It is generally not necessary to use complicated triode discrete components to make digital power amplifiers. It is directly based on the power supply voltage and output. The power can be selected from the corresponding digital power amplifier IC. Below we introduce a high-quality and low-cost stereo digital power amplifier circuit, the output power can reach 2x3W under 5V voltage.

one

A/D conversion and PWM modulation. In order to amplify the analog audio signal, A/D conversion is first required. After the analog audio signal is adjusted by PWM, it is converted into a digital signal whose pulse density is proportional to the input signal. The higher the instantaneous value of the signal voltage, the higher the pulse frequency. The greater the density, the lower the voltage, and the smaller the density. In this way, the analog audio signal is modulated in the digital pulse density for amplification by the switching tube of the subsequent stage.

two

power amplification. After the analog audio signal is converted into a PWM pulse train, it is used as the input signal of the amplifier to control the high-power switch tube for power amplification. Since the pulse signal only has high level and low level, the switch tube only works in saturation and conduction state. The loss is very small, the amplification efficiency is very high, the output voltage depends on the power supply voltage, the higher the power supply voltage, the greater the output voltage, so we get the amplified version of the pulse waveform.

three

filter output. After the pulse waveform is amplified by the pre-stage switch tube, since the PWM pulse frequency is much larger than the bandwidth of the audio signal, it cannot be directly used to drive the speaker, so a low-pass filter with a bandwidth of 20-20Khz is needed to demodulate the audio. Restore the original audio signal and drive the speaker to produce sound.

What is the digital age?

To put it simply, the digital age is synonymous with the electronic information age. Because all machine languages of electronic information are represented by numbers, people call it the digital age. Everything is based on electronic information, and information transmission is high-speed. It is convenient, but people will rely more and more on electric energy, and all kinds of electromagnetic radiation will come one after another, criss-crossing every corner of life, so there are advantages and disadvantages. So for audio, the product of the digital age is the birth of the hard disk HD player of the theater and the digital player and streaming media player of Hi-F audio.

For the hard disk HD player in theaters, it has entered many families, especially users who use 4K projectors are more willing to choose 4K ultra-high-definition hard disk player, because it can store more 4K movies and high-definition Movies, and at the same time, it has an advantage over 4K Blu-ray players in terms of cost performance. Digital players and streaming media players in high-fidelity stereos allow many friends who like to listen to music (especially the younger generation) to save more home space for CDs or LPs to store these software, but for them now It is hard to find a digital or streaming player that satisfies them both in terms of sound and price.