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Sampling period

Signal Processing Asked by John_HB on November 13, 2021

The signal $x(t)=e^{-t^2}text{sinc}(t)$ was sampled at interval $T$. It was then found that the discrete time Fourier transform of the sampled signal is: $X(e^{jomega})=1$. What is the minimum $T$ for which such a result is possible? If this is impossible for any $T$, explain why.

I started it but didn’t how to continue , any help? My steps so far:

begin{align}
x[n] &= e^{-n^2}text{sinc}[n] \
&= e^{-n^2}frac{text{sin}(pi n)}{pi n} \
&= frac{e^{-n^2}}{2j pi n}big(e^{jpi n} – e^{-jpi n}big) \
&= frac{1}{2j pi n}big( e^{jpi n – n^2} – e^{-jpi n – n^2} big) \
end{align}

begin{align}
X(e^{jomega}) &= 1 \
&= sum_{n=0}^{infty} x[n]e^{-jomega n} \
&= sum_{n=0}^{infty} frac{1}{j2pi n} big( e^{jpi n – n^2} – e^{-jpi n – n^2} big)
end{align}

One Answer

The best answer I could give is just a hint: think about what is the inverse discrete time Fourier transform of $X(e^{jomega})$. Constants in the frequency domain are what in the time domain? Answering that will lead you to the answer of this question.

Answered by Engineer on November 13, 2021

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