Hello,

I am designing a 2nd order bandpass sigma delta converter on Matlab and want to set the coefficients by using the Schreier Toolbox but unfortunately it does not give me the required modulated output.I am using a single bit quantizer,2 integrators first of which is a non-delaying and the second one is delaying,the center frequency if set to be 1/4 of the sampling frequency with an OSR of 128.I want to know whether the Schireir toolbox works fine for the Bandpass Sigma Delta or not?

If Any one here who has already worked on this one can help me it would be really great.

hello pancho_hideboo,

Thanks for your response.

I am posting the .m file.Here it is!!

%Parameters
order=2;
OSR=128;
opt=2;
H_inf=1.6;
f0=1/4;

nLev=2;
Nfft=2^13;
tone_bin=57;
t=[0:Nfft-1];
u=0.5*(nLev-1)*sin(2*pi*(tone_bin)/Nfft*t);
n=1:150;

%Synthesizing the NTF:
H=synthesizeNTF(order,OSR,opt,H_inf,f0);
form='CRFB';
[a,g,b,c]=realizeNTF(H,form);
b(2:end)=0;

%ABCD Matrix
[ABCD] = stuffABCD(a,g,b,c,form);
[ABCDs umax]=scaleABCD(ABCD,nLev=2,xLim=1);
[a g b c]=mapABCD(ABCDs,form);
[NTF STF]=calculateTF(ABCD);

%Pole Zero Plot,Rms Gain
plotPZ(H);
f=linspace(0,0.5,1000);
z=exp(2i*pi*f);
plot(f,dbv(evalTF(H,z)));
sigma_H=dbv(rmsGain(H,f0-0.25/OSR,f0+0.25/OSR));

%Plotting the Output in the time Domain
v=simulateDSM(u,H,nLev);
stairs(t(n),u(n),'g');
hold on;
stairs(t(n),v(n),'b')

%Calculating the Spectral Contents of the modulator
%Determining the SNR
spec=fft(v.*hann(Nfft))/(Nfft*(nLev-1)/4);
snr=calculateSNR(spec(1:ceil(Nfft/(2*OSR))+1),tone_bin);
NBW=1.5/Nfft;
Sqq=4*(evalTF(H,exp(2*pi*f))/(nLev-1)).^2/3;
f=linspace(0,0.5,Nfft/2+1);
plot(f,dbv(spec(1:Nfft/2+1)),'b')
hold on;
plot(f,dbp(Sqq*NBW),'m','Linewidth',1);

%The Dynamic Range plotting
%Peak SNR
amp=[-90:5:-20 -17:2:-1];
snr=simulateSNR(H,OSR,amp,f0,nLev);
plot(amp,snr,'-b',amp,snr,'db');
[pk_snr pk_amp]=peakSNR(snr,amp);

I don't check your M-file throughly.
There are still many wrong or improper issues in your M-file.

At least, the following code can work as BP-DSM.
You have to study why time domain waveforms are like these.

Code:

% The Designer's Guide Community Forum>Design>Mixed-Signal Design>Bandpass Sigma Delta Converter
% http://www.designers-guide.org/Forum/YaBB.pl?num=1213204643/0

close all, clear, clc
stdout = 1;

%Parameters
order = 2;
OSR = 128;
opt = 2;
H_inf = 1.6;
f0 = 1/4;

nLev = 2;
Nfft = 2^13;

Tstep = 1;
Textra = 100*Tstep;
Tstop = Nfft*Tstep + Textra;
delta_f = 1/(Tstop-Textra);

%tone_bin=57;
tone_bin = fix(f0/delta_f + 0.5);
if mod(tone_bin, 2) == 0
   tone_bin = tone_bin + 1;
end
fprintf(stdout, 'tone_bin=%d\n', tone_bin);

t1 = fix(Textra/Tstep);
t2 = t1 + Nfft-1;
t = 0:t2;
u = 0.5*(nLev-1)*sin(2*pi*(tone_bin)/Nfft*t);
n = 1:150;
n = n + t1;

%Synthesizing the NTF:
H = synthesizeNTF(order, OSR, opt, H_inf, f0);

%Pole Zero Plot,Rms Gain
figure(1), plotPZ(H); grid on
f = linspace(0,0.5,1000); z = exp(2i*pi*f);
figure(2), plot(f,dbv(evalTF(H,z)));
grid on
sigma_H = dbv(rmsGain(H, f0-0.25/OSR, f0+0.25/OSR));

%Plotting the Output in the time Domain
figure(3);
v = simulateDSM(u, H, nLev);
stairs(t(n), u(n), 'g');
hold on;
stairs(t(n), v(n), 'b')
grid on

%Calculating the Spectral Contents of the modulator
%Determining the SNR
figure(4);
spec = fft(v(t1:t2).*hann(Nfft))/(Nfft*(nLev-1)/4);
snr = calculateSNR(spec(1:ceil(Nfft/(2*OSR))+1), tone_bin);
NBW = 1.5/Nfft;
f = linspace(0, 0.5, Nfft/2+1);
plot(f, dbv(spec(1:Nfft/2+1)), 'b')
hold on;
Sqq = 4*(evalTF(H, exp(2*pi*f))/(nLev-1)).^2/3;
plot(f, dbp(Sqq*NBW), 'm', 'Linewidth', 1);
grid on

%The Dynamic Range plotting
%Peak SNR
figure(5);
amp = [-90:5:-20 -17:2:-1];
snr = simulateSNR(H, OSR, amp, f0, nLev);
plot(amp,snr, '-b', amp,snr, 'db');
[pk_snr pk_amp] = peakSNR(snr, amp);
grid on


form = 'CRFB';
[a,g,b,c] = realizeNTF(H, form);
b(2:end) = 0;

%ABCD Matrix
[ABCD] = stuffABCD(a, g, b, c, form);
xLim = 1;
[ABCDs umax] = scaleABCD(ABCD, nLev, xLim);
[a g b c] = mapABCD(ABCDs, form);
[NTF STF] = calculateTF(ABCD);
 

Why do you set tone_bin as 57 ?
I'm very curious about the theory or reason why you set tone_bin as 57.

tipu wrote on Jun 25^th, 2008, 4:25am:

See my modified M-File surely.
I read your M-File including syntax errors.

The followings are extraction of modified M-File.

Tstep = 1;
Textra = 100*Tstep;
Tstop = Nfft*Tstep + Textra;
delta_f = 1/(Tstop-Textra);

%tone_bin=57;
tone_bin = fix(f0/delta_f + 0.5);
if mod(tone_bin, 2) == 0
  tone_bin = tone_bin + 1;
end
fprintf(stdout, 'tone_bin=%d\n', tone_bin);

tipu wrote on Jun 25^th, 2008, 7:50am:

Yes. It is very very very common in SNR evaluation of sinusolidal signal using DFT.
You don't seem to understand DFT(FFT).
I think you should learn DFT before studying delta sigma modulation theory.

tipu wrote on Jun 25^th, 2008, 7:50am:

It is general.

tipu wrote on Jun 25^th, 2008, 7:50am:

Where do you want to locate zeros of NTF ?
Do you want to locate them around 20kHz ?
If so, this is Bandpass Delta Sigma not Lowpass Delta Sigma.

tipu wrote on Jun 25^th, 2008, 7:50am:

What do you mean by "an imaginary situation" ?

OSR=125, tone_bin=165

Code:

% The Designer's Guide Community Forum>Design>Mixed-Signal Design>Bandpass Sigma Delta Converter
% http://www.designers-guide.org/Forum/YaBB.pl?num=1213204643/0

close all, clear, clc
stdout = 1;

%Parameters
order = 2;
nLev = 2;
opt = 2;
H_inf = 1.6;

fs = 1e6;

%f0 = 1/4;
f0 = 20e3/fs; % Normalized by fs

%OSR = 128;
BW = 4e3;
OSR = fs/(2*BW);
fprintf(stdout, 'OSR=%d\n', OSR);

Nfft = 2^13;

Tstep = 1; % Normalized by (1/fs)
Textra = 100*Tstep;
Tstop = Nfft*Tstep + Textra;
delta_f = 1/(Tstop-Textra);

%tone_bin=57;
tone_bin = fix(f0/delta_f + 0.5);
if mod(tone_bin, 2) == 0
   tone_bin = tone_bin + 1;
end
fprintf(stdout, 'tone_bin=%d\n', tone_bin);

t1 = fix(Textra/Tstep);
t2 = t1 + Nfft-1;
t = 0:t2;
u = 0.5*(nLev-1)*sin(2*pi*(tone_bin)/Nfft*t);
n = 1:150;
n = n + t1;

%Synthesizing the NTF:
H = synthesizeNTF(order, OSR, opt, H_inf, f0);

%Pole Zero Plot,Rms Gain
figure(1), plotPZ(H); grid on
f = linspace(0, 0.5, 1000);
%figure(2), z = exp(2i*pi*f); plot(f,dbv(evalTF(H, z)));
figure(2), plot( f, dbv(squeeze(freqresp(H, 2*pi*f))) )
grid on
sigma_H = dbv(rmsGain(H, f0-0.25/OSR, f0+0.25/OSR));

%Plotting the Output in the time Domain
figure(3), hold on
v = simulateDSM(u, H, nLev);
stairs(t(n), u(n), 'g');
stairs(t(n), v(n), 'b')
grid on

%Calculating the Spectral Contents of the modulator
%Determining the SNR
figure(4), hold on
spec = fft( v(t1:t2) .* hann(Nfft) ) / (Nfft*(nLev-1)/4);
snr = calculateSNR(spec(1:ceil(Nfft/(2*OSR))+1), tone_bin);
NBW = 1.5/Nfft;
f = linspace(0, 0.5, Nfft/2+1);
plot(f, dbv(spec(1:Nfft/2+1)), 'b')
%z = exp(2i*pi*f); Sqq = 4*( evalTF(H, z) / (nLev-1) ) .^ 2/3;
Sqq = 4*( freqresp(H, 2*pi*f) / (nLev-1) ) .^ 2/3;
plot(f, dbp(squeeze(Sqq)*NBW), 'm', 'Linewidth', 1);
grid on

%The Dynamic Range plotting
%Peak SNR
figure(5);
amp = [-90:5:-20 -17:2:-1];
snr = simulateSNR(H, OSR, amp, f0, nLev);
plot(amp,snr, '-b', amp,snr, 'db');
[pk_snr pk_amp] = peakSNR(snr, amp);
grid on


form = 'CRFB';
[a,g,b,c] = realizeNTF(H, form);
b(2:end) = 0;

%ABCD Matrix
[ABCD] = stuffABCD(a, g, b, c, form);
xLim = 1;
[ABCDs umax] = scaleABCD(ABCD, nLev, xLim);
[a g b c] = mapABCD(ABCDs, form);
[NTF STF] = calculateTF(ABCD);