A digital amplifier with hi-fi signal controlled by DSP

Digital amplifier is widely used because of its high efficiency, compact size, environmental protection and anti-disturbance. However, it is difficult for a digital amplifier to achieve high fidelity due to switching characteristic, parasitic capacitance, internal resistance of power supply, voltage ripple and core loss of inductor. Especially, the internal resistance and core loss have great influence on signal of digital amplifier. This paper emphasizes the influence of the internal resistance of power supply on digital amplifier signal. In this paper, an equivalent circuit model of power stage can be deduced from the principle of difference amplifier. In this model, the amplitude of pulse wave decreases while duty ratio increases because of the existence of internal resistance of power supply. If pulse waves are converted into analog signal by LC filter, distortion could get more deteriorated. Therefore, a new control strategy, namely advanced compensation equation, is presented to achieve hi-fi signal for difference amplifier. Based on the equation, a compensated coefficient k increases linearly with the original PCM x, and k decreases with x. Test results show that this strategy is effective and correct.