Compensated methods for digital amplifier

Digital amplifier is widely used because of its high efficiency, compact size, environmental friendly and anti-disturbance. However, it is difficult for 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 influences on digital amplifier signal. So, these problems have to be discussed in two sections. On the basic principle of digital amplifier, it can be deduced that the value of peak flux density Bpk varies with pulse duration of PDM. Since core of iron power with ideal magnetic characteristics is often recommended for design of inductor of digital amplifier, Oliver model is fit to calculate the core loss. Due to the complexity of Oliver model and discrepancies of Steinmetz model, a new model of core loss is put forward. In the model, the original PCM signal can be compensated by utilizing an advanced compensation method. In addition, an equivalent circuit model of power stage can also be deduced from the principle of difference amplifier. In the model, it is found that the amplitude of pulse wave decreases while the duty ratio increasing because of the existence of internal resistance of power supply. When pulse signal can be converted into analog signal by LC filter, distortion of amplifier gets more deteriorated. So, another compensated equation is put forward to compensate the PCM signal. At last, the original PCM signal is compensated by the above mentioned methods. According to these compensated theories, a high fidelity signal of digital amplifier will be obtained. Test results do also prove that these methods are effective and correct.