Digital PA Amplifier: Fusion of Digital and Traditional, A Competent Assistant in the Audio Field

Digital PA amplifiers, a device playing a key role in the audio field, have undergone over a century of development since their inception in the 19th century. They are widely used in audio systems, televisions, wireless communications, radars, sonars, and many other fields, with their core function being the amplification of signal power. In sonar technology, digital PA amplifiers are indispensable, as they can increase the voltage and current of audio signals, thereby enhancing output power. This drives acoustic transducers to efficiently convert electrical signals into acoustic signals, emitting sound waves with sufficient energy into the ocean.

The concept of digital PA amplifiers was proposed as early as the 1960s, but progress was slow due to the technological limitations of that time. It wasn't until 1983, when Professor M.B. Sandler and others proposed the basic framework of the D-class (digital) PWM digital PA amplifier, that a solid foundation was laid for the development of digital PA amplifiers. D-class amplifiers stand out in the amplifier field due to their high efficiency and low power consumption. The amplification components operate in a switching mode. In the absence of signal input, they remain in a cutoff state, consuming no power. When there is a signal input, the components enter a working state, and the transistors saturate and conduct, directly connecting the power supply to the load. Ideally, the transistors have no saturation voltage drop, and the amplifier's efficiency can reach 100%. Although there is a slight saturation voltage drop in practical applications, the power consumption is unrelated to the signal output and is only related to the transistor characteristics, making them very suitable for ultra-high-power applications.

Working Principle of Digital PA Amplifiers

First, the input audio signal (whether analog or digital) is converted into a high-frequency PWM signal by a PWM signal converter. Next, these PWM signals are amplified to produce a PWM output with sufficient power. Finally, a low-pass filter is used to smooth the PWM signal, converting it into a high-power analog audio signal.

PWM modulators can be divided into analog signal PWM modulators and digital signal PWM modulators based on the type of input audio signal. Analog signal PWM modulators use a comparator to compare the analog input audio signal with a high-frequency carrier triangular wave signal. When their intersection occurs, a phase switching signal is output, which further controls the switching circuit to produce a PWM signal of a specific polarity. It is noteworthy that the frequency of the PWM signal remains consistent with the triangular wave signal, while its pulse width is directly determined by the amplitude of the analog input audio signal. Thus, the information of the audio signal is expressed through the pulse width of the PWM signal.

Advantages of Digital PA Amplifiers

Firstly, they exhibit excellent transient response. Because digital PA amplifiers do not need to handle the static current consumption of analog amplifiers, they can provide almost all the energy for audio output. Moreover, the lack of negative feedback and the restrictions of analog amplification endow digital PA amplifiers with outstanding "dynamic" characteristics.

Secondly, in terms of frequency response, digital PA amplifiers have no relative phase shift in the high, mid, and low-frequency bands, ensuring precise sound image positioning. This is achieved through the use of advanced technologies like digital filters and non-negative feedback amplification circuits, allowing the cutoff frequency of the output filter to be designed relatively high, thereby achieving flat amplitude-frequency characteristics and superior phase-frequency characteristics in the 20Hz to 20kHz range.

Additionally, digital PA amplifiers effectively avoid zero-crossing and crossover distortion issues.

Finally, digital PA amplifiers also hold potential for large-scale production.

In conclusion, digital PA amplifiers are devices used to increase the power of input signals and have widespread applications. Their primary function is to provide sufficient power output to meet the amplification needs of various systems and devices, serving as a valuable assistant in the audio field.