Class D Audio Power Amplifier With Dual-mode Control And Anti-distortion Function

Audio power amplifier is one of the essential equipments in sound system, whose main function is to amplify the weak electrical signals from a signal source so as to drive the loudspeaker. It is widely used in portable electronic products, home theater device and car audio. This thesis mainly focuses on the class D audio power amplifier. Comparing with other traditional audio power amplifiers, the class D audio power amplifier is characterized by low power consumption, high efficiency and small volume, which makes it more popular than the other traditional audio power amplifiers in portable mobile products.This thesis firstly describes the development process of the audio power amplifier and its basic theoretical knowledges briefly, including the principle and the classical circuit structure of the linear audio power amplifier and the switching audio power amplifier. Then two key design points of the class D audio power amplifier is mainly studied, including the dual-mode system and the anti-distortion system. The main work of the thesis is as follows.1. Based on the principle and design method of the class D audio power amplifier, the circuits of the function module in the basic class D power amplifier is designed through theoretical and experimental analysis, including pre-amplifier, integrator, oscillator, PWM modulator, output stage, over-temperature protection unit and over-current protection unit.2. Based on the realization of each module of the class D audio power amplifier, the dual-mode control system is proposed, which has the hardware control mode and the software control mode. The hardware control mode compares the magnitude of the input voltage and the standard voltage through the voltage control unit to make the system enter different work modes. The software control mode works through a series of pulses or rectangular wave, and the number of pulse and rectangular wave decides the work mode of the system.3. In order to improve the total harmonic distortion of the class D audio amplifier, the relevant signal processing and filter knowledge is studied. Moreover, an automatic gain change system is proposed. When the system detects the distorted output waveform, it automatically adjusts the loop gain according to the degree of distortion, which can make the output signal keep good shape.The designed circuit is implemented with CSMC 0.35 um process. Then, the module and the whole circuit are both simulated, and the whole layout is designed. Verification results show that the proposed dual-mode control, anti distortion class D audio power amplifier adjusts the distortion of the output signal very well in both the hardware control mode and the software control mode. Therefore, the proposed chip meets the design requirements.