| Compared with audio class A, B and AB linear power amplifiers, audio class D power amplifiers have higher power supply efficiency. In the situation that energy crises is more and more serious, audio class D power amplifiers are given more and more attention. The higher power supply efficiency of audio class D power amplifiers makes consumer electronic products using audio class D power amplifiers more portable, because batteries and heat sinks in these consumer electronic products can become smaller. Traditional audio class D power amplifiers consist mainly of analog circuits, so the design of them is complex and they are easily interfered by surroundings. However, except power stage, all portions of digital audio class D power amplifiers are implemented by digital circuits. Digital audio class D power amplifiers are easy to connect to audio digital signals, to implement and to transplant, and are not easily interfered by surroundings, so they are becoming a hot spot of present research.This paper focuses on digital audio class D power amplifiers using the method of pulse width modulation (PWM). Based on theoretical research and functional analysis for their system architecture and internal modules, this paper points out that the performance of digital audio class D power amplifiers will decline due to the nonlinearity of digital PWM generator and the effect of power supply noise in power stage. So a method of error online correction is presented in this paper, the method eliminates error caused by power supply noise in power stage and makes digital PWM generator linearized, through introducing power supply noise to the input of Sigma-Delta modulator and adding different correction factors to each integrator in sigma-delta modulator according to the ouput of Sigma-Delta modulator and power supply noise online.To verify the method of error online correction, this paper designs a digital audio class D power amplifier at system level. The digital audio class D power amplifier includes a high-performance low-complexity 8×interpolation filter, a 5-bit 8th-order Sigma-Delta modulator, a 32-level digital PWM generator and an H-bridge power stage. For the digital audio class D power amplifier system without error online correction, the maximal output noise-signal ratio (SNR) of the system is 27dB, which is bad. For the digital audio class D power amplifier system with error online correction implemented by the proposed method in this paper, the maximal output SNR of the system is 103dB, which indicates that the performance of the system is improved greatly and is enough to suit the need of high-performance audio power amplifier. |
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