September 3, 2007 -- Time-domain reflectometry will help you design and troubleshoot cables, connectors, fast PCB traces, and high-speed packages. With TDR instruments, you can ensure the signal integrity of fast digital signals as they travel across your system. Both analog and digital engineers need to understand and use these techniques.

September 3, 2007 -- TDR (time-domain-reflectometry) measurements can provide a direct representation of the signal integrity of a cable or PCB (printed-circuit-board) trace and can analyze ICs’ performance and failure. A TDR setup sends a fast pulse down the cable or PCB trace and displays the returning reflections, which indicate changes in impedance. The impedance changes can be radical, such as an open or a short, or they can be as subtle as the few femtofarads that a PCB via adds. The technique, in the form of OTDR (optical TDR), takes advantage of the equivalence between dielectric constants in electronic systems and the index of refraction in optical systems.

By Paul Rako, EDN Technical Editor