spectra of a sampled signal

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Alex_IC

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Hi!
Can somebody explain to me. Does the spectra of a sampled signal really have constant amplitude at every fa+/-n*fs, n=1,2,3 ... (fa - signal freq, fs - sampling freq ) ? In such a case the energy of the sampled signal is infinity!?
 

the spectra of discrete signal have a period of 2Π. then the spectra repeat.
also the energy isn't infinity. because in Parsval relation the integral done in 2Π domain.
 

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    Alex_IC

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you are talking on a digital signal. In general, the spectrum is repetitive and acts on the shape of a sinc function. example for that is the noise of a mixer or any digital circuit (where it is sometimes referred to as cyclostationary noise).
 

indeed the energy of sampled signal is infinity! but the power of this signal is finity!!!
please see the clasic book <Analog MOS Integrated Circuits for Signal Processing
> by Roubik Gregorian and Gabor C. Temes
 

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