sheldon
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Bharat,
The original explanation was a little simplified, there is a detailed discussion in the following sources,
James E. Solomon, “The Monolithic Op Amp: A Tutorial Study,” IEEE Journal of Solid-State Circuits, vol. sc-9, pp 314-332, Dec 1974
Grey, Hurst, Lewis, and Meyer, "Analysis and Design of Analog Integrated Circuits", fourth edition, page 639-644
When analyzing ampliers, the Miller Approximation allows designers to estimate the effect of an impedance connect across the amplifier as a capacitor, zA, at the input node. As a result the pole due the input node of the second stage is reduced, moves towards zero and the pole at the output of the second stage moves towards infinity. Since the frequency difference of the two poles is increased, the poles are said to be split.
For the reason that the second pole moves towards infinity, you should review the derivations in the references above. Just remeber that C[zA] is not the only terms in the expression for the second pole, rather C cancels some nasty terms in the second pole and thus the pole moves towards infinity.
Best Regards,
Sheldon
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