caosl_zju
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Posts: 22
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hi,all I have made a cascade2-1 sigma delta modulator as showed in the attached picture.Where parameters are:a1=a2=0.5,b1=2,c1=0.5,a3=0.5. The sampling frequency is 1Mhz,input signal is 0.2sin(2*pi*200).But the output bitstream amplitude is (+2,-2),This is linux matlab simulation result. Surprisingly, on my windows matlab, some of the output bitstreams has exceeded (+20,-20). If i change the parameter c1=1,thus 1/c1 is 1 too, the bit stream is (+1 -1). The PSD of it not embody the third order noise shapping effect at all,and the SNDR is very low(36dB,OSR=128). I have readed some papers about Sigma Delta modeling, but all the examples are sigle stage,one quantizer. Anybody can help me to solve this problem, or is there mash sigma delta modulator's simulink model? any advice is appreciative.Thanks!
Best Regards!
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