20Bit High-precision Sigma Delta Design Applied To Weak Signal Detection

Sigma Delta ADC plays an important part in analog to digital conversion circuits design,by oversampling,noise shaping and digital filtering techniques could reduce the complexity of analog circuits design and improve ratio of signal to noise. Sigma Delta ADC includes analog modulator and digital filter, the former one convert analog signal to digital signal, the latter one accomplish digital filtering process and finally,convert the high-speed stream to low-speed stream;Therefore,the Sigma Delta ADC design belongs to mixed-signal circuit design,requires more challenges for the design engineer.This paper reviews the various Sigma Delta modulator circuit structures at the first beginning.And then designer of this paper completes the MATLAB modeling and system simulation based on the Sigma Delta modulator module,analysises every Sigma Delta modulator module error factors and non-ideal factors.Finally,this paper lists the MATLAB system modeling analysises and simulation results, and also makes a deep analysis on the digital decimation filter and half-band filter including design principle and the design parameters, according to the sampling frequency,signal to noise ratio and other technical requirements,this paper completes digital circuits design with MATLAB tool, the circuits and layout are implementated in cadence environment,its total area is4.20mm*3.64mm,down-sampling rate is64times,the in-band ripple in lower frequency is0.0001dB,The measurement results indicate that after the digital filtering processing,output stream of Sigma Delta modulator achieves the requirement number of output bits.