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PSD of sigma delta ADc after decimation

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ali kotb

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Hello
I know how to plot the PSD after the modulator.
but I don't know how to plot it after Decimation filter ?
any advice, tutorials

Regards.
Ali
 

It is same as Nyquist ADC.

Assume Delta Sigma ADC of 3bits.
After decimation, bid width is wider, e.g. 16bits.

Then evaluate spectrum of 16bits data.
 
my ADC was 1 bit modulator
so I am confused for multibits data (after decimation)
how should the number of o/p bits affect this code that is used for 1 bit data :
Code: 
OSR=66; Nop=2^13;
w=hann(Nop); v=yout.*w;   % yout = o/p of analog modulator
NumUniquePts = ceil((Nop/(2*OSR)))+1; 
z=(fft(v,Nop))/(Nop*(nlev-1)/4);
b=z(1:Nop/2+1);
xm = abs(b); xm = xm.^2; 
f = linspace(0,0.5,Nop/2+1); %normalized freq.
semilogx(f,10*log10(xm),'b'); grid on;
 

ali kotb said:
my ADC was 1 bit modulator
so I am confused for multibits data (after decimation)
Click to expand...
Do you understand decimation filter ?

Most simple decimation filter is cic filter. Frequency characteristic of cic filter is same as moving averaging filter.
https://en.wikipedia.org/wiki/Cascaded_integrator-comb_filter

Output data of your ADC are +1 or -1, since resolution of your ADC is 1bit.

Consider output code 1,1,-1, 1,-1,-1, 1,1,1, -1,-1,-1,....
And assume moving average of 3 points.
Resulting data after cic decimation filter will be, 1/3, -1/3, 1, -1, ...
Data reolution is now 4 values, -1, -1/3, 1/3, 1.

If more points of averging are used, data resolution will be larger.
 
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