Behavioral Modelling of Delta Sigma Modulator

Dear friends,

I have been studying behavioral modelling for continuous time delta sigma modulator using Richards Schreir's "Understanding delta sigma converters". I have also pasted the image which is given on his book at page # 321. He has used some software for behavioral simulations which must yield at least the signal swings of the integrators. Which software should i use...MATLAB??? I don't think it can converge the specifications well!!! I need some simulation software for behavioral modelling....plz help!!!

HI samiurrehman
you can use LT-SPICE
you can download and find some tutorials on CMOSEDU.COM, and refer mixed signal design book by by J Baker

or Mentor Graphics if available.

Thanks for your reply, I have been using Cadence and verilog A for behavioral modelling but i have failed to get the required results. I shall download LTSpice and work with it. Have you ever used Proteus software. Do you think it is good for behavioral modelling of delta sigma structures.

I don't think LTSpice is good for you. It is a free SPICE software, capable to simulate to BSIM4. I've used Schreier's toolbox to simulate delta-sigma: it is written for MATLAB, and you can easily find it on the internet, it is free and available. It works fine and allows you to design some kind of sigma delta and test their responses. You can model several types of responses, choose the zeros positions, the loop filter order and so on. I don't know if you can use it for professional purposes, but i think is good enough to learn several things about delta-sigma. Other way are MATLAB scripting, using finite difference equations (i have used this approach for low order loops, with good results), SIMULINK, VHDL-AMS.

ViaDesigner has a Sigma Delta Modulator ADC design wizard that generates readable VHDL-AMS models for the analog and digital portions of Sigma Delta ADC. You can generate and simulate a variety of modulators using the ViaDesigner tool.

samiurrehman said:

I have also pasted the image which is given on his book at page # 321.
He has used some software for behavioral simulations which must yield at least the signal swings of the integrators.

Click to expand...

First, you have to scale coeffients according to reference voltage fullscale(VFS=25mV, in this example), permissible output fullscale voltage of integrator(500mV, in this example) and sampling frequency(fs=6.5MHz, in this example).

You can do this task by using "scaleABCD()" of Richards Schreir's MATLAB Toolbox(delsig).
However you have to relay on state conversion matrix S, since there is excess loop delay compensation path in this example.

S ; The diagonal scaling matrix
ABCDs = [S*A*Sinv, S*B; C*Sinv, D];

samiurrehman said:

Which software should i use...MATLAB???

Click to expand...

After getting scaled coefficients, you have to map them to R, C and Idac values.

After getting R, C and Idac values, you have to use Spice Type simulator such as Spectre, Hspice, eldo, etc, with Verilog-A.
Simulink modeling is not appropriate since both voltage and current are involved in this example.


There is a another caution for this example.
Quantizer is 1bit for this example.
So summation before quantizer using "c2" and "a3" is irregular.