When teaching students about how square waves with a finite rise time has a finite bandwidth, the question often arose:  "Is it the rise time or the slew rate of the edge which affects the bandwidth of the signal?". Few topics are as fundamental in signal integrity and create as much confusion as signal bandwidth. What exactly does bandwidth refer to and what features in the time domain influence bandwidth; rise time or slew rate? In this technical article, we show how the 3-dB bandwidth of a signal is defined, and why it depends on the rise time and not the slew rate.

The study was published as a technical article in the Signal Integrity Journal on May 4, 2021.