Can anyone explain me what is the effect on frequency spectrum due to  zero padding in a discrete time signal for interpolation ??
here i am attaching a pic from "cmos mixed signal circuit design by baker". here in the second fig even due after zero padding only the sampling frequency is shifted but rest of the spectrum is same. How is it possible ?

got it.... thanks....  but 1 more doubt... if after sampling, there is no aliasing i.e my sampling rate is greater than the nyquist rate, then how interpolation will be useful ???

but what is the advantage of changing the sampling rate ?
is their any benefit on the reconstruction filter design with up-sampling ?

but even after up-sampling, we have to remove image components. If we can't remove out of band components in the originally sampled signal completely then how can we remove image components in the up-sampled signal ?