EC-24.5 Signal Integrity and Power Integrity
You can decide when a trace must be treated as a transmission line, choose and place a termination, explain crosstalk in terms of coupling between adjacent traces, and read an eye diagram as a measure of margin.
Before:EC-2. Electromagnetics and Transmission LinesEC-17. Industry and Research Experience
The transmission line topic in the electromagnetics module gave you the theory; this is what it means for a board. The threshold is not the clock frequency but the edge rate: a slow signal with a fast edge behaves as a transmission line, and a great many designers have been surprised by that. Power integrity is the same physics applied to the supply, where the impedance seen by a chip has to stay low across a wide frequency range.
Work through these
When a trace becomes a transmission line, and why the edge rate decides
The comparison is between the signal's rise time and the round-trip delay along the trace, not between the clock period and anything. A slow clock with a sharp edge on a long trace will ring.
NPTEL: EMI, EMC and Signal Integrity — Principles, Techniques and Applications (IIT Kharagpur) · CourseReflections, and the four common terminations
A mismatch at either end sends energy back, and series, parallel, split and alternating-current terminations each fix it at a different cost in power and part count. Which is appropriate depends on the driver and the topology.
NPTEL: EMI, EMC and Signal Integrity — Principles, Techniques and Applications (IIT Kharagpur) · CourseCrosstalk: near end, far end, and the spacing rule that controls both
Two traces running close together couple through both capacitance and inductance, and the coupled voltage grows with the length they run in parallel. The usual remedy is separation measured in trace heights above the plane.
NPTEL: EMI, EMC and Signal Integrity — Principles, Techniques and Applications (IIT Kharagpur) · CourseMatched-length routing, skew and differential pairs
A parallel bus needs its bits to arrive together and a differential pair needs its two halves to stay in step. Both are met by matching physical length, which is why serpentine patterns appear on fast boards.
Power distribution impedance, and keeping it low across frequency
A chip demands current at frequencies from constant to gigahertz, and the supply network has to look low impedance across that whole range. Different capacitor sizes cover different parts of it, and their resonances can leave gaps.
NPTEL: EMI, EMC and Signal Integrity — Principles, Techniques and Applications (IIT Kharagpur) · CourseThe eye diagram as a picture of remaining margin
Overlaying many symbol periods shows how much room is left in both amplitude and time before decisions become unreliable. It is the standard evidence that a high-speed link works.
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