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Design >> Mixed-Signal Design >> Delta Sigma Problem
https://designers-guide.org/forum/YaBB.pl?num=1226319312

Message started by tipu on Nov 10^th, 2008, 4:15am

Title: Delta Sigma Problem
Post by tipu on Nov 10^th, 2008, 4:15am

Hello Everyone

I am working on a BP sigma Delta Modulator and lately got some results that i could not comprehend well.I am showing both the cadence and the matlab results as an attachment file.

The first one is that of matlab

and the second one is of cadence

Now I have 2 questions.

1) It seems that the notch is much sharper in the cadence as compared to that of matlab.In other words you can say that the cadence results look to do more noise shaping that the matlab results?? If this is so shouldn't it be the other way around and what is the possible cause of the behavior ?Also there is some difference in the noise floor .It is much flatter in matlab than in cadence

2) The second question is about the SNR calculation. How exactly can i determine the signal bins and the noise bins while calculating the SNR ?

Please Excuse my lack of knowledge in understanding the two things.Any help would be really of great value.

Thanks

Title: Re: Delta Sigma Problem
Post by tipu on Nov 10^th, 2008, 4:16am

and this one is the cadence result.

Title: Re: Delta Sigma Problem
Post by fonseca.ha on Nov 16^th, 2008, 9:48am

Are you still strugling with this inconsistency? I am not sure what it may be, but can you give more details? When you say cadence, do you mean a transistor level circuit?
Or do you mean behavioural models?
The issue may simply be the matlab model being too simplistic. But this is just a guess

Title: Re: Delta Sigma Problem
Post by gaom9 on Nov 23^rd, 2008, 6:20am

I think you should apply more detail about you simulation. What is your simulation way in cadence, by verilog-A or in transistor level?