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# Questions about Sigma-delta in dsp .

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##### Newbie level 6
(anybody Help me )Questions about Sigma-delta in dsp .

Hi,all
As we know, the output of the Sigma-delta modulator are bitstreams, such as ±1. In order to evaluate the performance of the modulator, we should use dsp technology.
I download a program from the net, which can calculate the SNR and PSD of the bitstreams. (the program is below)
My questions are:
1. why we should extracts sinusoidal signal?
2. If the bitsteams are not ±1, for example, they are 2bits Quantizer. Then the Vref is what , 1 too?

Here is the program:

function [snrdB, ptotdB, psigdB, pnoisedB] = calcSNR(vout,f,fB,w,N,Vref)
% SNR calculation in the time domain (P. Malcovati, S. Brigati)
% vout: Sigma-Delta bit-stream taken at the modulator output
% f: Normalized signal frequency (fs -> 1)
% fB: Base-band frequency bins
% w: windowing vector
% N: samples number
% Vref: feedback reference voltage ———————— If the bitsteams are not ±1, for example, they are 2bits Quantizer. Then the Vref is what , 1 too?

%
% snrdB: SNR in dB
% ptotdB: Bit-stream power spectral density (vector)
% psigdB: Extracted signal power spectral density (vector)
% pnoisedB: Noise power spectral density (vector)
%
fB=ceil(fB);
signal=(N/sum(w))*sinusx(vout(1:N).*w,f,N); % Extracts sinusoidal signal ——————why we should extracts sinusoidal signal? is it in common use ?

noise=vout(1:N)-signal; % Extracts noise components
stot=((abs(fft((vout(1:N).*w)'))).^2); % Bit-stream PSD
ssignal=(abs(fft((signal(1:N).*w)'))).^2; % Signal PSD
snoise=(abs(fft((noise(1:N).*w)'))).^2; % Noise PSD
pwsignal=sum(ssignal(1:fB)); % Signal power
pwnoise=sum(snoise(1:fB)); % Noise power
snr=pwsignal/pwnoise;
snrdB=dbp(snr);

norm=sum(stot)/Vref^2; % PSD normalization
if nargout > 1
ptot=stot/norm;
ptotdB=dbp(ptot);
end

if nargout > 2
psig=ssignal/norm;
psigdB=dbp(psig);
end

if nargout > 3
pnoise=snoise/norm;
pnoisedB=dbp(pnoise);
end

Last edited:

Hlp :???:

dogrun

### dogrun

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Up Up Up ， can anybody help me ？plz

Re: (anybody Help me )Questions about Sigma-delta in dsp .

My questions are:
1. why we should extracts sinusoidal signal?
Ans. Generally the input test signal we apply is a sinusoidal signal during simulations, hence this custom function is apparently performing this task.

2. If the bitstreams are not ±1, for example, they are 2bits Quantizer. Then the Vref is what , 1 too?
Ans. It depends on the quanitizer levels, for example if we have a NRZ 1 bit Quantizer Vref +1, -1 ; for RZ 1 bit quanitizer then the Vref are +1 ,0

for a 2 bit Quantizer Vref if its NRZ the Vref is the same +1 , -1 except that we now have to bits at the input rather than one. similarly for RZ etc.

I hope it helps.

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