$8$

Multiple choice

$10$ points

A $100$ kHz continuous$-$time signal is passed through a LPF$,$ sampled, and then subsequently passed through a recovery circuit to recover the original continuous$-$time signal.

The recovered signal contains significant spectral components below $100$ kHz $($in the region of $40-70kHz)$ that were not present in the original, in addition to components at $100$ kHz $.$

What could be $($a$)$ possible explanation$($s$)$ for this?

The signal was over$-$sampled.

The signal was under$-$sampled.

The LPF before sampling had a cut$-$off frequency lower than $100$ kHz $.$

The LPF before sampling had a cut$-$off frequency higher than $100$ kHz $.$

The recovery filter had a cutoff$-$frequency lower than $100$ kHz $.$

The recovery filter had a cutoff$-$frequency higher than $100$ kHz $.$

None of the above are suitable explanations.

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