Applied In The Field Of Mobile Class D Audio Amplifier Design

With the rapid development of the mobile technology in recent years, a high-efficiency power amplifier meets great market. Class D amplifiers modulate the input signals and the modulated signals usually are two-level signals to drive the power transistors switch. Then the output of the power transistors is filtered by a low-pass filter. Finally the output of the low-pass filter drives the load, usually a speaker. Ideally the efficiency of the class D amplifier is 100% and practically it can achieve 80%～95%. The high efficiency makes the class D amplifier more and more important in mobile power amplifier applications. The common modulation technologies in the class D amplifier are pulse-width modulation and sigma-delta modulation. The sigma-delta modulation technology is used in this paper.A differential input, differential output class D amplifier with sigma-delta modulation is implemented with 0.18um 1.8V/3.3V Mixed Signal CMOS process. The sampling clock is 2.56MHz. The bandwidth of the input signal is 20 kHz. The oversample ratio is 64. The operation voltage is 3.3V. The simulation results show it consumes 0.6mA under 3.3V supply voltage and 80% of efficiency can be achieved. The SNR (signal to noise ratio) is 55dB and the THD (total harmonic distortion is 0.2% with a 2 kHz,0.7V amplitude sine input signal. And 50% of efficiency is achieved.