spectra of a sampled signal

[Alex_IC]

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!?

 

[salam2000]

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.

 

[Jim cage]

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).

 

[langtaosha]

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