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Before a continuous system can be controlled digitally, the continuous input signal must be converted into a discrete signal. This process involves two critical steps described by Kuo: The 1st edition (Prentice-Hall, 1977) is out of
Kuo emphasizes the Sampling Theorem (Shannon-Nyquist), which states that to reconstruct a continuous signal from its samples without aliasing, the sampling frequency $\omega_s$ must be at least twice the highest frequency component present in the signal ($\omega_s > 2\omega_max$). Kuo emphasizes the Sampling Theorem (Shannon-Nyquist)