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.