Comprehensive analysis of the difference between digital power amplifier and analog power amplifier
First, the difference between digital power amplifier and Class D power amplifier, common class D power amplifier ( PWMpower amplifier) Working Principle: PWMpower amplifier can only accept analog audio signals, and compare the triangular waves generated by the internal triangular wave generator with it. The result is a pulse width modulation signal (PWM) , Then amplify and restore the PWM signal to an analog audio signal. Therefore, PWMpower amplifier simulates the analog audio amplitude with pulse width, and the information transmission process is simulated, non-quantitative, and non-coded. Moreover, due to the limitation of current device performance, PWMpower amplifier cannot adopt too high sampling frequency and cannot reach Hi-Level of Fi. The digital power amplifier uses some fixed-width pulses to digitally quantify and encode analog audio signals, making the restoration of audio signals more realistic. Second, the difference between digital power amplifier and analog power amplifier. Digital power amplifier has overcome some inherent shortcomings of analog power amplifier because its working style is completely different from that of traditional analog power amplifier, and has some unique features. 1. Overload capacity and power reserve, the overload capacity of digital power amplifier circuit is much higher than that of analog power amplifier. Analog power amplifier circuits are divided into Class A, Class B or class AB power amplifier circuits, and the power amplifier tube works in the online area during normal operation; When overloaded, the power amplifier tube works in the saturation region, with harmonic distortion, exponential increase in distortion degree, and rapid deterioration of sound quality. The digital power amplifier is always in the saturation zone and the cut-off zone when the power is amplified. As long as the power amplifier tube is not damaged, the distortion will not increase rapidly, as shown in Figure 1. Because the digital power amplifier adopts a switching amplifier circuit, the efficiency is extremely high, reaching 75% ~ 90% ( The efficiency of analog power amplifier is only 30% ~ 50%), Basically do not get hot at work. Therefore, it does not simulate the static current consumption of power amplifier, and almost all energy is reserved for audio output. In addition, there is no analog amplification and no negative feedback before and after, therefore, it has better 'power' characteristics, good transient response and strong 'explosion feeling. 2. Crossover distortion and mismatch distortion simulate Class B power amplifier distortion at zero crossing, which is caused by the nonlinear characteristics of transistors at small current at the positive and negative intersections of output waveforms ( When the signal is small, the transistor will work in the cut-off area without current passing through, resulting in serious output distortion). However, the digital power amplifier only works in the switching state and does not cause crossover distortion. The analog power amplifier has the mismatch distortion of the upper and lower asymmetry of the output waveform caused by the inconsistent characteristics of the push-pull to the tube. Therefore, when designing the push-pull amplifier circuit, the requirements for the power amplifier tube are very strict. However, the digital power amplifier has no special requirements for the pairing of switch tubes and can be used basically without strict selection. 3. The matching of power amplifier and speaker will be loaded when matching speakers with different resistance values due to the large internal resistance of power amplifier tubes in analog power amplifier (Speaker)The effect of size. The internal resistance of digital power amplifier does not exceed 0. 2Ω (Internal resistance of switch tube plus internal resistance of filter), Relative to load (Speaker)Resistance value (4 ~ 8Ω) It is completely negligible, so there is no matching problem with the speaker. 4. Transient Intermodulation distortion, analog power amplifier almost all use negative feedback circuit to ensure its electroacoustic index. In negative feedback circuit, in order to suppress parasitic oscillation, phase compensation circuit is adopted, therefore, transient intermodulation distortion will occur. The digital power amplifier does not use any analog amplification feedback circuit in power conversion, thus avoiding transient intermodulation distortion. 5. For analog power amplifier, there is generally a phase difference between the output signal and the input signal, and the phase distortion is also different when the output power is different. The digital power amplifier uses digital signal amplification to make the phase of the output signal and the input signal completely consistent, and the phase shift is zero, so the audio-visual positioning is accurate. 6. The upgraded digital power amplifier can obtain high power by simply replacing the switch amplification module. The high-power switch amplification module has low cost and broad development prospects in the professional field. 7. Production debugging, analog power amplifier has debugging problems at all levels of work points, which is not conducive to mass production. The digital power amplifier is mostly a digital circuit, which can work normally without debugging, especially suitable for large-scale production. Third, the difference between digital power amplifier and 'digital' power amplifier and 'digital' power amplifier, the so-called 'digital' power amplifier only uses digital signal processing in the front stage, after analog audio signal or digital audio signal input, the existing digital audio processing integrated circuit is used to realize some functions such as sound field processing, digital delay, reverberation, etc, finally, audio amplification is performed by analog power amplification module. The typical circuit block diagram is shown in figure 2. As can be seen from Fig. 2, the interfaces of each module are simulated. The general principle block diagram of the digital sound field processing module is shown in figure 3. Although all IC manufacturers have introduced digital sound field processing, digital karaoke and Digital Dolby decoding integrated circuits. However, since most of the current power amplifier can only receive analog audio signals, the interfaces of each integrated circuit are mostly analog, which requires repeated module/number, number/mode conversion, this will introduce quantitative noise to worsen the sound quality. All digital power amplifier in addition to the interface for speakers ( This is because the current speakers can only accept analog audio signals) Audio signals are processed in the form of digital signals inside power amplifier (Including power amplification); For analog audio signals, they must be converted into digital signals before processing. The introduction of digital power amplifier in an era where digital audio is already available may have a significant impact on the development of audio technology.