Loss At The Nyquist Frequency: Why 25 Gbps Is Specified At 12.5 GHz Interface specifications are often written in terms of a data rate, and the loss limit is applied at half that number. The reason is that a non return to zero signal is a series of symbol transitions,…

Finding EMC Weak Points Before the Compliance Test Most products fail an immunity test in a specific place, at a specific frequency, and for a reason that is not visible on the schematic. The failure is usually the consequence of one small structure: a trace that acts as an antenna,…

EMC Magnetic Cores: Mechanism and Selection A magnetic core fitted around a cable is one of the few electromagnetic compatibility measures that can be added to an existing product without changing the board. It produces no signal, amplifies nothing, and does only one thing: it removes high frequency energy from…

Via Optimization For High Speed Channels A via is a short vertical section of transmission line with a length that depends on the board thickness and a geometry that no two dimensional model describes well. On a slow net it is a connection; on a fast channel it is a…

Checking Reference Plane Splits Before Release A reference plane split is one of the few layout defects that is invisible in every standard check and fatal in the finished product. The netlist is correct, the clearance rules are satisfied and the connectivity is complete, yet any signal that crosses the…

Gold Finger Plating and Beveling for Edge Connectors Gold fingers are the part of a board that a mating connector grips, slides against, and wears every time the product is inserted. They are also one of the few features whose specification combines plating, geometry, and mechanical finishing in a single…

First Article Inspection of a PCB: What Is Checked First article inspection is the point at which the first production board is measured against the drawing rather than against expectations, and it is the cheapest opportunity in the whole program to find a discrepancy. Skipping it moves the discovery to…

Why a Conductive Foam Gasket Underperforms in the Product A conductive foam gasket is specified from a datasheet that quotes a shielding effectiveness of eighty decibels or more, and after assembly the product measures ten decibels worse. The natural reaction is to suspect the material and to look for a…

The Assembly Drawing and What It Must Carry An assembly drawing is the document that tells the production floor what to build, and it is usually the least maintained document in the package. Where it is wrong, the board is built wrongly and the mistake is invisible until test. What…

Lost Steps in Stepper Drives: An EMC Diagnosis A machine tool cutting an irregular arc, a depth of cut that varies from pass to pass, and edges that look rough rather than machined: the symptoms point at the motion control system, and the first response is usually to replace the…