Design Of Sigma-Delta Modulation Type Class D Power Amplifier

Digital power amplifiers as an important branch in the history of digital development greatly promoted the development of engineering technology with its good anti-EMI interference,stable working mode and low loss,efficient output characteristics,and widely used in the field of video and audio,sonar detection,radio frequency modulation and logging transmission system.However,the core of digital power amplifier lies in the modulation mode of its switching pulse signal.On the basis of consulting relevant literature,aiming at the shortcomings of existing pulse modulation modes such as low precision and poor anti-EMI,this paper proposes a fully digital class D power amplifiers modulation scheme using the Sigma-Delta modulation algorithm which commonly used in the field of D/A chip design,so that the system can directly modulate and output digital signals without D/A conversion.The research contents are as follows:Firstly,this paper introduced the classification of power amplifiers and development of modulation techniques.Based on the analysis of the basic modulation model of digital power amplifier,the Sigma-Delta modulation was analyzed in theory.Then the oversampling technology and noise shaping technology which affected the signal-to-noise ratio of the modulation system in Sigma-Delta modulation system were theoretically analyzed and mathematically deduced.Secondly,the digital up conversion structure used in Sigma-Delta modulation algorithm and the stability performance of Sigma-Delta modulation module were analyzed theoretically.A digital up conversion scheme which combine half-band interpolation filter with CIC interpolation filter was proposed and the parameters were calibrated.The structure of high-order Sigma-Delta modulator was optimized.With the help of Simulink tool,the mathematical model and feasibility analysis of the designed Sigma-Delta modulation system were carried out.Thirdly,each functional module of digital Sigma-Delta modulation system was realized by using the Verilog hardware description language through the top-down logic design scheme using the FPGA chip,and the synthesizable RTL logic code was simulated,synthesized,layout and routing,and timing analysis.The high sampling rate digital signal was modulated to 1 bit pulse signal output.Finally,H-bridge complementary symmetrical output and low-pass filter circuit were used as the class D power output stage of the system.The digital up-conversion module and noise shaping module in Sigma-Delta modulation system were tested and analyzed respectively,and the signal-to-noise ratio performance of the modulation system was evaluated.The feasibility of applying Sigma-Delta modulation algorithm to digital class D power amplifier system was verified.