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pankaj jha

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20 Dec 2013 Delta Sigma Toolbox High-level design and simulation of delta-sigma modulators Author: Richard Schreier

I am trying to implement a Band Pass Sigma Delta modulator SDM using delsig toolbox.

These are the MATLAB commands that I am running to get the modulator coefficients:
NTF = synthesizeNTF(4,320/(2*10),0,1.5*1,0.25);
STF = zpk([-1 , 1 , -1 , 1],[-0.2302 - 0.7241i , -0.2302 + 0.7241i , 0.2302 - 0.7241i , 0.2302 + 0.7241i],0.0976,[ ]);
[a,g,b,c] = realizeNTF(NTF,'CRFF',STF);
The MATLAB outputs:

a =

0.5558 0.2435 0.0436

g =

8.5267e-004

b =

0.1316 -1.0603 4.4905 0.3558

c =

1 1 1

This is wrong because there should be 4 coefficients for 'a' vector, whereas what we get only 3 coefficients for vector 'a' . Similarly is the case for vectors'b', 'c' and 'g'.

What could be possibly wrong?

30 Oct 2012 Delta Sigma Toolbox High-level design and simulation of delta-sigma modulators Author: Richard Schreier

I am trying to implement a SDM using delsig toolbox. The following are the commands I try to run, along with the errors.

H = synthesizeChebyshevNTF(2,12.5,1,1.5,0);
>> stf = zpk([],[],1,1) ;
>> [a g b c] = realizeNTF(H,'CRFFD',stf)
Error using /
Matrix dimensions must agree.

Error in realizeNTF (line 246)
a = -real(zL1/T);

Can you suggest me how to rectify the error???

29 Mar 2012 Delta Sigma Toolbox High-level design and simulation of delta-sigma modulators Author: Richard Schreier

Respected Sir,

I am trying to simulate a sixth order sigma delta modulator using the
"Delta Sigma Toolbox".

1) My desired NTF is a 6th order Chebyshev type II high pass filter.
Hence, I ran the following command :
>> ntf = synthesizeChebyshevNTF(6,64,2,1.5,0)

The toolbox outputs the function given below:
Zero/pole/gain:
(z^2 - 2z + 1) (z^2 - 1.999z + 1) (z^2 - 1.998z + 1)
-----------------------------------------------------------------------
(z^2 - 1.629z + 0.6655) (z^2 - 1.705z + 0.7437) (z^2 - 1.854z + 0.8979)

Sampling time: 1

2) I wish to implement the above NTF using the "CIFB" structure. So
I ran the following command:
>>[a,g,b,c] = realizeNTF(ntf,'CIFB')
which gives the output
a =

0.0001 0.0013 0.0124 0.0794 0.3223 0.8120

g =

0.0002 0.0022 0.0012

b =

0.0001 0.0013 0.0124 0.0794 0.3223 0.8120 1.0000

c =

1 1 1 1 1 1

3) I tried to construct the "CIFB" structure using the coefficient
values provided by the toolbox, mentioned in the previous step.

4) I try to analyse the frequency content of the output (y2 in the
simulink file attached with this mail). I ran the following commands :
>> NFFT = 2^nextpow2(length(y2)); % Next power of 2 from length of y
>> Y = fft(y2,NFFT)/length(y2);
>> f = 300e6/2*linspace(0,1,NFFT/2+1);
>> plot(f,2*abs(Y(1:NFFT/2+1)))

5) The output is more like a low pass filter and not a high pass expected.

Hence, i request you to kindly have look at the .mdl file and the
commands executed by me, and help me find the mistake that I have
committed.

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