Study Of Digital Audio Amplifier Based On Sigma Delta Modulator

In the audio amplifier domain, approximately 95% of amplifier is based on the traditional analog technology which has been used for more than 10 years. Such kind of amplifier has shortcomings of low efficiency. Class D audio power amplifier, which works in switching mode, has advantage of high efficiency and thus becomes one of the most promising audio amplifier solutions. Most of traditional class D amplifier solutions are based on PWM (pulse width modulator) modulation technique, with its input as analog audio wave (sine wave), which is compared with triangle wave (or saw-tooth wave) to output PWM waves to control the power switch mosfets in switching status. Thus it can only amplify anlog signals.The thesis introduces the sigma delta modulator (SDM) technique to replace PWM technique. Its input is digital audio sources and it can directly amplify digital signals. It omits D/A circuit which is a must in traditional class D amplifier, it is therefore a real digital audio power amplifier. It combines with oversampling technique, and has excellent noise shaping effects. It can put quantize noises to the high band of signals, so with low pass filter, it can output high SNR audio signal. This technique provide a way to realize a high efficience and high fidelity audio power amplifier.The thesis compares analog audio amplifier with digital audio amplifier, and compares traditional class D amplifier with class D amplifier based on SDM. The analysis of SDM used in class D and the stability of high order SDM are performed. A kind of stable SDM is designed and simulations are performed to verfy the analysis results.