Sigma Delta Modulator in Matlab

[engrMunna]

Hi. I am trying to find a transfer function for a 2nd order sigma delta modulator using the sigma delta tool box in matlab.
using the following code

ntfo =synthesizeNTF(2,512,2,1.5,0) %%%synthesizeNTF(order,osr,optimization,Hinf,f0);
[ABCDc,tdac2] = realizeNTF_ct( ntfo, 'FB', tdac);
[Ac Bc Cc Dc] = partitionABCD(ABCDc);
sys_c = ss(Ac,Bc,Cc,Dc);
sysf = tf(sys_c)

the output that I get is


Transfer function from input 1 to output:
0.2164
------
s^2

Transfer function from input 2 to output:
-0.6667 s - 0.2164
------------------
s^2


What I dont understand is what does it mean by input 1 and input 2 ? why are there two inputs ? is the second input the quantization noise? please help thanks

 

[singhji0000]

did u get the answer for this?

 

[pancho_hideboo]

What I dont understand is what does it mean by input 1 and input 2 ?
why are there two inputs ?

Y=L0*U+L1*V
U is an input 1.
V is an input 2.

See "MODULATOR MODEL DETAILS" of "DSToolbox.pdf".

 

[singhji0000]

i need some example model to plot the output code vs input analog voltage in matlab. OSR 128, Vref 2.9 , Nbits = 16

it will be really helpful if u have some example.

 

[pancho_hideboo]

i need some example model to plot the output code vs input analog voltage in matlab.
OSR 128, Vref 2.9 , Nbits = 16

You have to specify followings.

- DSM Type ; LP? BP?
- Input Frequency
- Center frequency of DSM if you choose BP-DSM.
- Input Level relative to Full Scale. Full Scale will be 2*Vref=5.8Vpp in your case.
- Order of DSM
- OSR

See The Designer's Guide Community Forum - Bandpass Sigma Delta Converter

 

[singhji0000]

hello,

specs mentioned below:

DSM Type ; LP
- Input Frequency --- DC input for the time being
- Center frequency of DSM if you choose BP-DSM.----- NA
- Order of DSM ---- order 1
- OSR = 128

i was able to model 1st order integrator in matlab ( not using simulink as i m asked not to use it for time being) and got step response for output code vs input DC analog voltage.
i have set one flag for offset , and thus i get two set of values of output codes wrt to analog input... for eg one set of values when i enable offset and when i disable offset. Now my question is how to plot error plot which generally comes in saw tooth manner.