Scopes display eye diagrams for serial trigger and decode

June 28, 2016 // By Graham Prophet
Teledyne LeCroy is expanding the serial data analysis capabilities of its oscilloscopes by introducing eye diagram capabilities in its TDME Serial Bus options.

The added capability will display an eye diagram of a packetized low-speed serial data signal without additional setup time. Eye parameters quantify system performance; users can apply a standard or custom mask to identify anomalies. Mask failures can be indicated and can force the scope into Stop mode. Up to four serial data signals can be decoded and displayed as eye diagrams at one time. These can be different protocols, or the same protocol measured at different points (e.g., transmit and receive, different nodes, or different standard-defined test points). A user-defined filter may be applied to each eye diagram to only display specific signals in the eye.

The signal quality of physical layer can be qualified in the eye by applying parameters for eye height, eye width, and number of mask failures. Some packages (e.g., FlexRay TDMP) go a step further and include additional measurements defined in the standard. A user-defined or pre-defined mask may be added to the eye diagram so as to objectively evaluate if the physical layer signal intrudes too far into the eye opening. Filters can include or exclude specific messages from the Eye so as to determine failure source (e.g., messages from a specific node or with a specific ID). Mask failures are indicated with a red circle and can be displayed in a table. Touch the failure table to open a zoom of the failed area for further inspection.

Some standards, due to their speed or nodal complexity, provide specific guidance on what eye diagrams or measurements should be made and exactly how they should be performed. FlexRay and MIPI DPHY are examples. In these cases, the Eye Diagram (“E”) capability is augmented with additional specialized “P” capability (for Physical Layer Measurements), as per the standard.