Digital Module Design Of Sigma-Delta Audio Out System

Audio out system is an important part of a multimedia SoC chip. It isused to make the conversion from digital audio data to the analog signalswhich can be heard by people. Nowadays, people have more and morerequirements on the distortion and SNR persormance of the audio system.So, the DA convertor based on Sigma-Delta modulation has become thehotspot of the research because of its high SNR performance.This paper emphasized the digital module design of a Sigma-Deltamodulator, described the detailed design flow of this module, and madethe improvements on the interpolation filter and the Sigma-Deltamodulator module to get the higher SNR performance.First, this paper introduced the datapath design of the system. Itsupports more PCM code format than tranditional systems to save theCPU resources for software conversion.Then, this paper described the detailed design flow of an interpolationfilter. We compared the structures of different digital filters and selectedone which is more flexible and more suitable for a SoC chip. We design the parameters of the filter to meet the requirent of the performance.Sigma-Delta modulator is the most important module in this system. Itdirectly decided the performance of the whole system. Except theadvantages of the modulator, it still can not give an ideal SNR for theinputs which is under a small level. This paper analyzed the structure ofthe modulator and put forward an adapted method to solve this problem.This improvement can make a high SNR performance for a lage range ofthe input levels.This design started from the theories, implemented by Verilog HDLlanguage, synthesized by DC tools, and taped out using0.18um technics.This paper listed all the verification result of the design, including matlabsimulation result, RTL verification result and the test result after tape out.All this can give the guarantee of the industrial production.