raja.cedt wrote on Dec 2nd, 2010, 7:32pm:hi,
The main advantages i could see is implicit anti -aliasing filtering
and variations in the the input impedance of the modulator is less so that poles and zero locations of the loop won't change much.
The first point is clear of course. You have implicit antialiasing which helps a lot in some cases.
The second point is a bit obscure to me. Why should the loop pole/zero locations have anything to do with the input impedance. At any rate, the fixed absolute location of poles/zeros in the NTF is one of the major DISADVANTAGES of using a continuous-time modulator, especially since you are likely to want to use a modulator for different frequency ranges, e.g. in case you want to make it for a wireless application, then for different standards.
A discrete-time solution in this case is more elegant as the NTF remains independent of the operating clock frequency, allowing the same modulator to be scaled and used for different applications, provided that the settling requirements are always fulfilled.
And there lies the catch. Since discrete-time modulators require very good settling and are typically realized in form of switched-capacitor filters, they consume much more power for the same operating frequency, and are also not useful once you start clocking at really high rates.....
There are other differences too of course, but these seem to be the most important ones.
Vivek