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Design >> Analog Design >> Delta sigma modulator
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Message started by vivekrc on Aug 22^nd, 2004, 7:40pm

Title: Delta sigma modulator
Post by vivekrc on Aug 22^nd, 2004, 7:40pm

I would like to design an 125MHz delta sigma modulator with sampling frequency 2.5GHz using switched capacitor adder, integrator, multiplexer, one bit quantizer in the feedforward loop and one bit Digital to analog converter in the feedback loop. The multiplexer will choose input plus the reference voltage or the input minus the reference voltage depending on the output from the one bit DAC.
I would like to know whether this design will work for IBM 0.13 micron technology.
Actually, i dont know how to design a switched capacitor adder, can anyone suggest me the design.
Thanks.

Title: Re: Delta sigma modulator
Post by Vivek on Aug 31^st, 2004, 1:07am

Hi,

I doubt if you can actually design a modulator with the kind of clock frequency you mention. In any case, it would be quite a job to make the simplest of circuits work at 2.5 GHz. On top of that, you wish to make a SC circuit which would require opamps with UGBW atleast 7 times the clock rate. I quote this number because you are talking of a SC delta-sigma modulator without giving any more info such as the desired resolution and whether or not your modulator has to be a baseband delta-sigma or a bandpass delta-sigma. I think narrowband designs might be possible but you will not use SC integrators but resonators there.

Please check to see your design specs. If someone wants you to design a baseband delta-sigma with such specs, then it might be a joke of some sort.

You can find a good deal of information about designing delta-sigma ADCs (including bandpass delta-sigma ADCs) along with switched-capacitor circuits in the following references (also on many other sources on the net and in print):

(1) "Delta-Sigma Data Converters: Theory, Design & Simulation" by Norsworthy, Schreier and Temes, IEEE Press.
(2) "Analog MOS Integrated Circuits for Signal Processing" by Gregorian and Temes, John Wiley & Sons.
(3) "Analog Integrated Circuit Design" by Johns and Martin, John Wiley & Sons.