Contents I. Introduction
Conventional linear power amplifiers are still widely used in many industry applications especially in audio power amplification and some special fields because of the high fidelity, high bandwidth and excellent dynamic performance. However, the linear amplifiers exhibit low efficiency due to the constant power supply voltage, and dissipate a lot of power with bulky power supply and large heat sinks [1]. On the other hand, the switch-mode power amplifiers, often called class D amplifiers, are very power efficient with little power dissipation, because the power devices in the switch-mode power amplifiers are operate in on/off mode with low power losses. Then the class D amplifiers can be small and light in weight without heavy heat sinks. Just because of this switch-mode operation, however, the output fidelity of the class D amplifier is low. The total harmonic distortion (THD) introduced by the switching operation is high. A class D amplifier requires an external low pass filter to remove the high frequency carrier and recover the input signal. However, if the output waveform has to be of very high quality the filter has to be properly designed and to be in general of higher order type. But this filter will reduce the dynamic response and increase the output impedance of the amplifier, so the load influences the distortion and the system frequency response.
