Signal integrity signifies the signal’s ability to propagate without distortion.Signal integrity is nothing but the quality of the signal passing through a transmission line. Fundamentally, signal integrity issues must be taken care during the PCB design phase. Once the board has been designed, there is little one can do to improve signal integrity.
A simple analogy for your understanding:
AM signal -> not so clear (distorted signals)
FM signal -> more clear (better signal integrity)
To be more descriptive, signal integrity is the measurement of the quality of an electrical signal typically in electronic printed circuit boards. In digital electronics, a stream of binary values is represented by a voltage (or current) waveform. However, digital signals are fundamentally analog in nature, and all signals are subject to effects such as noise, distortion and loss.
Daniel Beeker and Rick Hartley explained, “Ringing is the result of having the driver farther away from the receiver than 1/4th wavelength. This results in a first order reflection of more than the incident wave that returns to the driver and becomes a depletion wave at a lower voltage going back to the receiver, until all of the energy finally either goes into the receiver, is converted to heat in the conductors and dielectric or mostly radiates.”
Daniel Beeker and Rick Hartley said, “A stub is a single piece of conductor, and unless there is a pair of vias next to each other - one ground and one signal - or a signal via and a ground plane, the field does not see the stub except as very high impedance.” A via stub acts like a resonant circuit with a specific resonant frequency at which it stores maximum energy within it. If the signal has a significant component at or near that frequency, that component of the signal will be heavily attenuated due to the energy demands of the via stub at its resonant frequency.