Signal Integrity


Today's electronics is mostly consisting of digital circuits, processors, memory, and I/O devices. Their main method of communication is via digital serial/parallel interfaces which is consist of clock and data interface.  To ensure correct transmission of data from one system to another, that is the role of signal integrity check.


Digital signal is almost always transmitted with reference to a clock signal. The transmitter, transmission medium, and receiver are not perfect, and signal distortion can be easily introduced in form of voltage and timing error resulting in poor reception and detection of data. In this the text, we present commonly seen signal integrity problems, its cause, and address some best design practice to mitigate these problems.

Common Signal Integrity Problems

Impedance mismatch

impedance mismatch for high speed interface on a trace with transmission line effect  causes signal reflection. We identify a trace of having a transmission line effect is by evaluate whether nor not the trace length exceeds at least 10 times the lowest electrical wavelength of the highest frequency signal.

Common cause

Length mismatch(timing skews) for differential signaling


Path loss

Test setup

Passive vs Active probe


Eye diagram

A eye diagram is a quick and instant visual check on timing and voltage margin of the signal received the receiver. The more open the eye has the higher the margin for receiver to detect logic 1 or 0s.  Various high speed interface has its own eye opening requirements. Generally a eye mask, indicator of timing and voltage margin,  for various serial interface is standardized in the industry that that it can be use to determined the signal integrity of the interface.

All errors found on Eye Diagram are lumped into two categories, timing and voltage.

Timing Errors (Horizontal (i.e timing/phase noise))



Voltage Errors (Vertical (i.e voltage ripple))


Summary and Conclusion

Almost all electronics design has been digitized in modern time. As a system engineer focusing on digital system, ensuring signal integrity in digital communication system is critical to the over functionality of your computing system or else control and data can't not be communicated reliable across all digital subsystems.

Reference and Further Reading

"The Three Most Confusing Topics in Signal Integrity ",