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https://designers-guide.org/forum/YaBB.pl Design >> Mixed-Signal Design >> Delta-Sigma Modulator, Feedforward or Feedback?? https://designers-guide.org/forum/YaBB.pl?num=1244215608 Message started by OpAmp on Jun 5th, 2009, 8:26am |
Title: Delta-Sigma Modulator, Feedforward or Feedback?? Post by OpAmp on Jun 5th, 2009, 8:26am I was wondering if anybody can introduce me a document comparing the feedback and feedforward structures of delta sigma modulators? I have read the following two books (Delta-Sigma Data Converters by Norsworthy et al and Understanding Delta-Sigma Data Converters by Schreier and Temes) regarding this topic and couldn’t find the pros and cons of the two structures. For higher order delta-sigma DACs, I usually see feedforward structure is used, but I don’t quite understand why!!! You comments are really appreciated. OpAmp :-) |
Title: Re: Delta-Sigma Modulator, Feedforward or Feedback?? Post by Berti on Jun 23rd, 2009, 3:37am Hi, I try to give you a brief overview: Advantages of Feedforward compared to Feedback: Lower signal swing at the output of the integrators (beneficial for amplifier design), larger first loop filter coefficient (better noise suppression than feedback structure), single DAC only, and depending on the implementation the feedforward structure might recover from instability without additional circuitry. Disadvantages: The summing node in front of the quantizer. In general I think that the lower signal swing is the main motivation why feedforward structures are preferred nowadays. Cheers |
Title: Re: Delta-Sigma Modulator, Feedforward or Feedback?? Post by Sumit Adhikari on Aug 14th, 2009, 1:08am Both of them has completely different usage as per as frequency domain is considered. in feedback topology you introduce conjugate zeros in your transfer function as a result a low pass transfer function (say in feedforward SDM) changes itself into a bandpass (feedback) transfer function. Lower or higher signal swing is an architectural design issue and has nothing to do with topology. The usage of the input signal swing is decided by the choice of coefficients. Please go through book "Data Converters" by Franco Maloberti Regards, Sumit |
Title: Re: Delta-Sigma Modulator, Feedforward or Feedback?? Post by boa on Aug 18th, 2009, 7:21am Sumit, I believe you misunderstood the question: the discussion here is about 2 different architectures (feedback or feedforward) of SDM with low-pass NTF. Bandpass SDM is completely a different story.. |
Title: Re: Delta-Sigma Modulator, Feedforward or Feedback?? Post by Berti on Aug 18th, 2009, 10:47pm Yep Boa. Sumit, read the paper following paper: J.Silva et al., "Wideband low-distortion delta-sigma ADC topology", Electronics Letters. Cheers |
Title: Re: Delta-Sigma Modulator, Feedforward or Feedback?? Post by vivkr on Aug 20th, 2009, 3:00am Berti wrote on Aug 18th, 2009, 10:47pm:
Ah! but that is an Electronics Letters paper, a fat chance that anyone has a subscription to that one. So get it from the source directly: http://web.engr.oregonstate.edu/~moon/research/files/el_jun07_01.pdf Best regards, Vivek P.S.: There is also a lot of other useful stuff on this page. Just look around. |
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