As a hardware engineer, especially for pure analog circuits and audio power amplifiers, you should be familiar with Class A, class B, class AB, class D, class G, class H and class T power amplifiers. Most engineers may only know a part of it, or know about it. In order to let more engineers master more detailed knowledge of audio power amplifier, the following is a detailed description of the above audio power amplifier.

Power amplifier, as the name suggests, is the abbreviation of power amplification. Compared with voltage or current amplification, power amplifier requires to obtain certain and undistorted power, and generally works in large signal state. Therefore, power amplifier circuit generally includes special problems that voltage amplification or current amplification circuit does not have, which are shown as follows: ① the output power is as large as possible; ② it usually works in large signal state; ③ nonlinear distortion is prominent; ④ it is necessary to improve efficiency Important concerns; ⑤ the safety of power devices. For audio power amplifier circuit, we also need to pay attention to the above problems.

According to the different conducting ways of amplifier circuits, audio power amplifier circuits are classified into analog and digital types. Analog audio power amplifier usually has class A, class B, class AB, class G, class h, TD power amplifier, while digital circuit power amplifier is divided into class D and class t. The following is a detailed introduction and analysis of the above power amplifier circuit.


Class a power amplifier


Class a power amplifier is as shown in the figure above. There is no current cut-off (i.e. output stop) in the whole cycle of the signal. However, A-type amplifier will produce high heat and low efficiency. Although class a power amplifier has the above disadvantages, its inherent advantages are that there is no crossover distortion, and there are some inherent advantages in its internal principle. It is an ideal choice for replaying music. It can provide very smooth sound quality, round and warm sound, transparent high frequency, full and transparent medium frequency. Single ended amplifiers are class A, push-pull amplifiers can be class A, class B or class A.


Class B power amplifier


Class B power amplifier is a kind of amplifier whose positive and negative half cycles of sinusoidal signal are amplified and output by two transistors of push-pull output stage in turn. The conduction time of each transistor is half cycle of the signal, which usually produces what we call cross distortion. Through the adjustment of analog circuit, the distortion can be reduced or even disappeared as far as possible. The efficiency of class B amplifier is obviously higher than that of class a amplifier.


Class AB Power Amplifier

Class AB power amplifier is between Class A and class B. the turn-on time of each transistor in push-pull amplifier is more than half a cycle of the signal but less than one cycle. Therefore, class AB power amplifier effectively solves the problem of class B amplifier’s Cross distortion, and its efficiency is higher than that of class a amplifier, so it has been widely used.



Class D power amplifier (also known as class D power amplifier)


Class D power amplifier, also known as digital amplifier, uses a very high frequency conversion switch circuit to amplify the audio signal. The specific working principle is as follows: Class D power amplifier adopts asynchronous modulation. When the audio signal cycle changes, the high frequency carrier signal remains unchanged. Therefore, when the audio frequency is relatively low, the number of PWM carriers is still high, so it is necessary to suppress the high frequency carrier The frequency conversion band of carrier wave is based on the frequency of audio signal, so there is no interference between carrier wave and fundamental wave. Many Class-D amplifiers with power up to 1000W are just as big as VHS video tapes. This kind of amplifier is not suitable for wide band amplifier, but it is widely used in active subwoofer.


Class G power amplifier

Class G power amplifier is an improved form of class AB Power Amplifier with multi power supply. Class G power amplifier makes full use of the advantage that audio has a very high peak factor (10-20db). Most of the time, the audio signal is in a low amplitude, and it will show a higher peak value very rarely. The figure below is a typical functional block diagram of class G power amplifier IC.


The class G amplifier uses an adaptive power rail and a built-in buck converter to generate a positive power supply voltage for the headphone amplifier. The charging pump reverses the positive supply voltage of the amplifier and generates the negative supply voltage of the amplifier. This allows the headphone amplifier output to be concentrated at 0V. When the amplitude of audio signal is low, the buck converter generates a negative supply voltage of low amplifier. In this way, the power consumption of class G amplifier is minimized while playing low noise and high fidelity audio. Compared with the traditional class AB headphone amplifier, class G amplifier has higher efficiency.

The amplification principle of this kind of power amplifier is the same as that of class AB power amplifier. One important feature is that the power supply part adopts two or more groups of voltage. Low voltage is used for low power operation, and high power is automatically switched to high voltage.


Class h power amplifier

The principle of the amplifier circuit of this kind of power amplifier is the same as that of class AB power amplifier, but the power supply part adopts the switching power supply with adjustable multi-stage output voltage, which can automatically detect the output power and select the supply voltage.


Class k Power Amplifier

Class k power amplifier is integrated with internal bootstrap boost circuit and various power amplifier circuits. As we all know, class D power amplifier is only one of the most efficient digital power amplifiers in many power amplifier circuits, while class k power amplifier only integrates the internal bootstrap boost circuit and the required power amplifier circuit according to the needs. If the efficiency is high, class D power amplifier will be added, and class AB power amplifier will be added if the sound quality is good.


Class T power amplifier

The principle of this kind of power amplifier is the same as that of class D power amplifier, but the signal part adopts DDP Technology (the core is small signal adaptive algorithm and prediction algorithm). The working principle is as follows: the current of the audio signal into the speaker is all processed by DDP, and then the high-power high-frequency transistor is controlled to turn on or off, so as to achieve the high fidelity linear amplification of the audio signal. This kind of power amplifier has high efficiency, small distortion, and the sound quality can be comparable to that of class AB power amplifier.


The figure above shows the internal module structure of ta2020. It can be seen from the figure above that the chip mainly focuses on processing and modulation modules, so as to achieve the characteristics of high-quality audio.


Class TD power amplifier

The amplifying part of this kind of audio power amplifier has the same principle as class AB power amplifier, but the power supply part adopts completely independent high-precision adjustable stepless output adjustable digital power supply, the progressive value of voltage is 0.1V, and the automatic detection of power can adjust the rise or fall of voltage. This kind of power amplifier needs a high-precision adjustable digital power supply, so it needs a special design of the power supply, and can not be concentrated on one chip. Therefore, this kind of power amplifier is mainly used in high-end audio, and the circuit is also more complex.

For the latter 6, 7 and 9 types of power amplifiers, special power supply is needed, so the function cannot be concentrated on one IC. For classic class A, class B, class AB and class D power amplifiers, there are special ICs. In the actual design, we need all kinds of power amplifier circuits applied in different fields. We only need to add the corresponding power supply or processing module on this basis.

In order to help you master the basic circuit principle and design of op amp, and systematically study hardware circuit design, the editor has prepared a collection of basic hardware knowledge of super system + actual combat data of circuit project design, so as to give you a complete study of the whole process of hardware circuit product development. Through the systematic learning of content, we can help you to sort out the basic knowledge and theory of hardware engineer from 0 to 1: understand components, see circuits clearly, be able to do demand analysis, product performance design, learn to analyze and design circuits, master unit circuit, integrated circuit and complex circuit design, be able to design circuits independently, do product project research and development, and become an independent hardware R & D Engineer!

Hardware engineer must know audio power amplifier circuit

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