Composition and classification of the hottest digi

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Composition and classification of digital audio power amplifier

digital audio power amplifier is a kind of pulse signal that converts the input analog audio signal or PCM digital information into PWM (pulse brightness modulation) or PDM (pulse density modulation), and then uses PWM or PDM pulse signal to control the high-power switching device to turn on/off the audio power amplifier. Also known as switching amplifier and class D amplifier, it has outstanding advantages of high efficiency. The digital audio power amplifier also looks like a one bit power digital to analog converter. The amplifier is composed of input signal processing circuit, switching signal forming circuit, high-power switching circuit and low-pass filter

the input signal forming circuit is divided into PWM Processor and PDM processing, which transforms the amplitude change of the input signal into the change of pulse width or pulse density

high power switching circuits are divided into head bridge and full bridge (BTL connection). High power switching devices used bipolar crystal triodes in the 1970s. Now, almost all n-channel MOS FETs are used. In half bridge mode, the working states of the upper and lower pipes are opposite, and the pipes on the two diagonals are opposite, and the pipes are connected and disconnected in turn in full bridge mode

the function of low-pass filter is to integrate the pulse waveform into a beautiful analog waveform, that is, to filter the carrier component of PWM or PDM signal. LC filter with low power loss is often used

the most classical circuit in digital amplifier is the way of using voltage comparator and triangular wave generator in switching signal forming circuit. The constant amplitude trigonometric test generated by the trigonometric wave generator is compared with the analog signal, and converted into PWM signal. This method is easy to be affected by the inconsistency of component parameters and parameter changes, and it is usually necessary to introduce negative feedback in the input

△∑ PDM digital amplifier is the method adopted by sharp and other companies that stipulate the number of missing edges and corners and the number of cracks, also known as △∑ one bit amplifier. The switching signal forming circuit uses a one bit output △∑ modulator to transform the analog signal into PDM signal. Usually, in order to improve linearity, negative feedback is introduced from the output body of the △∑ modulator

the input signals of the above two digital amplifiers are analog signals. Now the sound source has been mainly digital, so all digital amplifier has become the inevitable trend of the development of digital amplifier. Delta sigma PWM digital amplifier has high transmission accuracy. It is a way of all digital amplifier. The beginning signal forming circuit of the all digital amplifier is composed of bit conversion circuit and PWM conversion circuit. The function of the bit conversion circuit is to convert the input PCM signal into a low bit PCM signal, and then convert the low bit PCM signal into a PWM signal through the PWM conversion circuit. The high end of the bit band and the reduction of signal-to-noise ratio deterioration caused by bit compression use a multi bit output △∑ modulator. Feedforward compensation is used in the PWM conversion circuit, which outputs two PWM signals and eight BTL drives. The two PWM signals are opposite and have a complementary relationship of 2, so that the transformation errors caused by the characteristics of the output group switching devices cancel each other in the high-power starting circuit. Therefore, this circuit can achieve little distortion without introducing negative feedback

pdm signal is a pulse with the same amplitude and time width, but the density of the pulse changes with the simulation. Therefore, PDM signal is a bit signal in both amplitude and time axis directions. The PWM signal is a pulse with amplitude and frequency, and the pulse width changes with the amplitude of the analog signal. Therefore, the amplitude direction of PWM signal is a one bit signal. In order to ensure the same signal-to-noise ratio and dynamic range, the switching frequency of PDM mode is higher than that of PWM mode, and the switching frequency can reach several MHz. For example, the switching frequency of Sharp's sm-sx2000 is as high as 5.6448mhz. The switching frequency of PWM mode can be low, but the master clock frequency is low, which is n times of the switching frequency

the head frequency of PDM mode is low, so it is necessary to use switching devices with small input power, and the on resistance of such switching devices is often too large. On the contrary, the PWM mode can choose the switching device with small on resistance, so the efficiency of the first circuit is 85%, and check whether each limit switch works at the same time, and the general PWM amplifier can achieve a high efficiency of more than 90%

at present, Ti and Sony have developed special integrated circuits for digital audio amplifiers, especially those with uneven distribution, and used these integrated circuits to produce a variety of all digital amplifiers, some of which are developed for market users. At the same time, various companies are also carrying out various research on reducing the number of soldiers in the industry. (end)

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