Paul
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Hi George,
I did not have time to check your code, I just went over it quickly. I was not able to open your plots with either Paint or Imaging (Win2k)... Are you able to provide a more conventional format (e.g. gif, jpeg, tiff,...) or let me know which tool to use to read these files (not even Gimp was able to read it). Further more I never used hAMSter, but I heard about it. I am lucky enough to have a licence for Advance MS from Mentor.
One major difference I noticed when going from a 1st-order to a 2nd-order modulator is the introduction of the ILA block. I would suggest a step-by-step approach, introducing one novelty at each step. This means I woul first add the additional integrator with an ideal DAC (no mismatch). If the result is OK, I would add the ILA (with no mismatch), check again the result. Finally, I would add mismatch to the DAC and see if the ILA compensates correctly.
BTW, regarding the tool question: As the whole modulator is a discrete-time system and you are using real operations, you could model (almost) everything in your model in pure VHDL instead of using VHDL-AMS. I don't know if you intend to use non-idealitites later. If you don't, using VHDL would speed up your simulation time and let you use other free simulators with complete language support.
Please let me know about the results of the mentioned approach.
Paul
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