Test Challenges for PAM4 Signals

The major test challenges posed by PAM4 signals

PAM4 encoding offers the advantage of doubling the bit rate in a serial data channel, doing so by increasing the number of voltage levels from two to four. It's a fairly complex modulation scheme, so it should be no surprise that it presents some test and measurement challenges.

Why High Oscilloscope Sampling Rates Matter

Figure 1: Here is an example of aliasing that results from
sampling a signal at less than the Nyquist rate of 2f_max

A key to accurate measurements with an oscilloscope is to ensure that the instrument maintains a high sampling rate. This applies to most measurements; conversely, for many measurements, accuracy may suffer as sample rate decreases. In the worst case, some signal components may be "aliased," meaning that the true signal shape is corrupted by the addition of bogus signal components that arise from undersampling of real signal components.