To calculate the Speed Rating, the measured -7 dB point is rounded up to the nearest half-GHz level. The up-rounding corrects for a portion of the test board’s trace loss. The resulting loss value is then doubled to determine the approximate maximum data rate in Gigabits per second (Gbps).

For example, a cable assembly with a -7 dB point of 7.8 GHz would have a Speed Rating of 8 GHz/ 16 Gbps. A cable assembly with a -7 dB point of 7.2 GHz would have a Speed Rating of 7.5 GHz/ 15 Gbps.

The Samtec Speed Rating is best considered as a figure of merit for comparing relative performance between cable assemblies. The Speed Rating becomes less meaningful in systems using multi-level signaling or where crosstalk or impedance mismatch are more critical parameters.

Modern high speed digital transceivers can accommodate roughly 9 dB of loss and still operate reliably. This is based on transmitter levels of roughly 600 mV, receiver sensitivities of 100-200 mV and no equalization. Typical system channel budgets allocate a higher loss budget for cable assemblies than for individual connectors and this practice is reflected in the cable assembly speed rating at Samtec. The -7dB rating is a conservative number that allocates 2 dB of system budget for other channel components such as short PCB traces and IC packaging effects.

The updated Samtec Speed Rating is reflected in our most recent High Speed Characterization Reports. However, our older reports still detail the -3 dB point in the insertion loss plots. If there is any confusion with this discrepancy, please contact our Signal Integrity Group.

For assistance in determining a cable assembly’s suitability for specific high speed applications, please contact our Signal Integrity Group.

If you would like assistance in interpreting Samtec’s Speed Ratings, please contact our Signal Integrity Group.