Research On Class D Amplifier Based On Sigma-delta Modulation

Audio power amplifiers are the core components of consumer electronics such as MP4 s,mobile phones,media players.Class D amplifiers gradually replace traditional linear power amplifiers for small size,low loss,and high efficiency.However,Class D power amplifiers has harmonic distortion and electromagnetic interference(EMI),and extra analog filters increase system volume.The sigma-delta modulation utilizes oversampling and noise-shaping technique to reduce low-frequency noise and distortion.The three-level topology is superior to traditional two-level topology with a smaller dv/dt,switching loss,thereby further reducing harmonics and EMI,especially the T-type three-level topology.While Analog D-class power amplifiers have temperature drift issues.The rapid development of digital storage technology has made the digital Class D amplifier a new hot spot.This paper first analyzes the principle of sigma-delta modulation and the basic structure of the sigma-delta modulator.In order to improve the bridge error caused by unbalanced voltage drop of the switch and by the dead zone,the sigma-delta modulation based on the mid-point of the bridge arm was introduced.Based on the second-order sigma-delta modulation,the analog circuit of the class-D power amplifier is designed with a single-phase half-bridge circuit.The experimental results show that the class-D power amplifier has a good function of wide-band signal amplification.Secondly,the digital implementations of two-level and three-level Class-D power amplifiers based on first-order sigma-delta modulators are studied.To solve high harmonics and large dv/dt problems in two-level circuits,T-type three-level topologies were introduced.The T-type three-level operation principle and three-level sigma-delta modulation are analyzed.The sigma-delta modulation of three-level circuit is realized through the introduced threshold parameters.The influence of threshold is studied and a reasonable threshold parameter is established.The influence of dead zone on system performance is analyzed and T-type class D amplifier system adopted by sigma-delta modulation based on the mid-point feedback of the bridge arm is established.The Matlab/Simulink simulation studies the performance of the two modulation methods and the two topologies.Finally,experiments of 50 Hz sine wave have been done for both 2-level and 3-level digital class-D amplifier using FPGA.The results show that the mid-point feedback modulation of the bridge arm has better performance than the inner loop modulation and three-level has better performance than two-level topology.