Advantages of Class D power amplifiers:
1. High energy conversion efficiency, small size, and high reliability. The power consumption is only one-third of that of analog amplifiers of the same power level. The actual efficiency of its power supply can reach over 90%, saving energy and meeting environmental requirements. However, the efficiency of Class B amplifiers is only 78% of the theoretical value, which should generally be only 30-40% in practice. The efficiency of Class A power amplifiers is even lower. Due to the extremely high efficiency of Class D power amplifiers, the temperature rise of semiconductor devices is significantly reduced, and the distortion rate is also significantly reduced.
2. The minimum load impedance that can be connected can be very low, and the power conversion efficiency remains basically unchanged regardless of the load impedance.
3. There is no relative phase shift in high, medium, and low frequencies, and the sound is clear and transparent, with accurate sound image positioning. Due to the use of 16 amplification circuits without negative feedback, digital filters, and other processing techniques, the cutoff frequency of the output filter can be designed to be high, ensuring flat amplitude frequency characteristics and good phase frequency characteristics within 20Hz~20kHz.
4. Good transient response, i.e. good "dynamic characteristics". Due to the fact that it does not require the static current consumption of traditional power amplifiers, almost all energy is reserved for audio output, and there is no analog amplification or negative feedback constraints, it has better "power" characteristics. Due to the extremely small voltage drop of Vds when the FET transistor used in Class D power amplifier is on, the maximum amplitude of the output audio voltage of Class D power amplifier is close to the supply voltage. However, linear power amplifiers, due to the influence of static bias and Vces, have a certain gap between the maximum output audio voltage amplitude and the power supply voltage, which is more obvious in low-voltage systems.
5. No zero crossing distortion. Traditional power amplifiers generally have zero crossing and Crossover distortion distortion due to poor tube pairing and adjustment at all levels.
6. Directly receiving coaxial or fiber optic digital audio signals output from digital audio sources such as CDs and DVDs, it can be directly amplified in the form of digital signals, reflecting the perfect combination with digital audio sources.
7. Suitable for mass production. The consistency of the product is good, and there is no need for debugging during production. The reliability is good, as long as the components are installed correctly.
8. It is convenient to achieve functions such as remote control, group control, and monitoring without the need for any additional devices.
Although Class D power amplifiers have many advantages mentioned above, they also have their own shortcomings, and it is precisely these shortcomings that have been constraining the progress of Class D power amplifiers.
Shortcomings of Class D power amplifiers:
1. The output power transistor is not a pure switch, nor is it well matched, which can cause distortion.
2. During the process of turning on and off power transistors, the potential of the grounding point will fluctuate, thereby increasing noise.
3. The power output circuit is a bridge circuit formed by connecting two power transistors, one of which is on and the other is off, with a dead zone between them.
4. A low-pass filter is used between the power output circuit and the speaker to filter out components other than audio, allowing the audio signal to enter the speaker. However, it is not possible to completely filter out pulse width modulated carriers, which is also a factor causing distortion. Causing distortion of the speaker.
5. The EMI problem is severe, and when using a single modulation frequency of ordinary PWM for modulation, the components of high-frequency harmonics are large, which may cause serious EMI problems.
6. It is very sensitive to the jitter of the sampling clock, and small jitters in the sampling clock frequency can cause significant distortion. The shortcomings of actual Class D power amplifiers are constantly being improved through technological advancements, and their inherent high efficiency advantages are also constantly being strengthened. It is believed that in the future, Class D power amplifiers will comprehensively replace Class A/B/AB power amplifiers, especially in situations where higher power and efficiency are pursued.
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