| In recent years, along with the coverage of the MP3,PDA,notebook,car stereos and other portable multiple media, class D power amplifier has become more and more popular than traditional linear one due to its high efficiency and small volume. Hence, class D power amplifier is of great application value and market prospect.Based on the analysis of the traditional audio amplifier, some improvements on the circuit topology have been made and a new class D power amplifier with high efficiency, low distortion and output filter-free is designed. And the following techniques have been taken: a dead-time control circuit is introduce to cutoff the current dissipation due to the upper and lower power transistors conduction at the same time; and a dual anti-width modulation technique is adopted to reduce the static consumption; a dual-loop feedback circuit is proposed to drop the nonlinear distortion and improve the power supply rejection; a sigma-delta noise shaping technique is used to lower the noise; a low pass filter is implemented by the parasitic inductance, reducing the system volume; a fully differential topologic is adopted to improve the resistance to common mode interface. Additionally, in the input stage, a special low noise amplifier is used to improve the noise performance and a programmable variable gain amplifier is introduced, making the volume adjustment precise and flexible.In the design of the audio amplifier, behavior level modeling in Matlab and mixed simulation between behavior level and transistor level technologies are proposed in order to reduce the simulation time needed in circuit optimization.Designed in VIS_MX3n5 CMOS process, Cadence simulation results indicates that this circuit, with 5V power supply for output stage and 8ohm load, has less than 60nv/√Hz input referred noise, less than 0.02% THD, higher than 85% efficiency, 1W maximum output power with non-distortion,±32dB adjustable gain range and 2dB/step gain variation with less than 0.4dB gain error. |
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