Nyquist Frequency

Originally, it is a sampling theorem in the digitization of analog signals, which means that "only frequencies up to half the sampling frequency can be reproduced". In turn, it is also used as a term to indicate the frequency that is the main component of a digital transmission signal. In NRZ, 1/2 of the data rate is the Nyquist frequency, and in the method called PAM4, which vertically overlaps 2 bits, it is 1/4.