power_pwer
Junior Member level 1
dear all:
happy new year! and i need your help with the discrete fourier transform for my first order
sigle bit sigma delta modulator output.the problem is like this:
the input signal is sig=1.5+0.5*sin(2*pi*200K*t);then i FFT the signal:sig1=1.5+0.5*sin(2*pi*K/100)(K=1,2,3....400). the results of this FFT are F(1)=600;F(5)=F(397)=100;F(any other point)=0;
however,after the signal pass the first order sigle bit modulator(sampling frequency is 20M),400 points bitstream is got,then I FFT the bitstream,the results become:F(1)=600;F(177)=F(225)=102.5643;F(5)=F(397)=101.0066;F(169)=F(233)=89.7403;......
my question is: why are the two results different? and why the values on the harmonic frequency are not zero in the practical system output?
happy new year! and i need your help with the discrete fourier transform for my first order
sigle bit sigma delta modulator output.the problem is like this:
the input signal is sig=1.5+0.5*sin(2*pi*200K*t);then i FFT the signal:sig1=1.5+0.5*sin(2*pi*K/100)(K=1,2,3....400). the results of this FFT are F(1)=600;F(5)=F(397)=100;F(any other point)=0;
however,after the signal pass the first order sigle bit modulator(sampling frequency is 20M),400 points bitstream is got,then I FFT the bitstream,the results become:F(1)=600;F(177)=F(225)=102.5643;F(5)=F(397)=101.0066;F(169)=F(233)=89.7403;......
my question is: why are the two results different? and why the values on the harmonic frequency are not zero in the practical system output?