ZHCSDJ6E February 2015 – June 2018 LMH1218
PRODUCTION DATA.
The LMH1218 has an on-chip eye opening monitor (EOM) which can be used to analyze, monitor, and diagnose the performance of the link. The EOM operates on the post-equalized waveform, just prior to the data sampler. Therefore, it captures the effects of all the equalization circuits within the receiver before the data is reclocked. The EOM is operational for 1.485 Gbps and higher data rates.
The EOM monitors the post-equalized waveform in a time window that spans one unit intervals and a configurable voltage range that spans up to ±400 mV differential. The time window and voltage range are divided into 64 steps, so the result of the eye capture is a 64 × 64 matrix of “hits,” where each point represents a specific voltage and phase offset relative to the main data sampler. The number of “hits” registered at each point needs to be taken in context with the total number of bits observed at that voltage and phase offset in order to determine the corresponding probability for that point. The number of bits observed at each point is configurable.
A common measurement performed by the EOM is the horizontal and vertical eye opening. The horizontal eye opening (HEO) represents the width of the post-equalized eye at 0-V differential amplitude, measured in unit intervals or picoseconds. The vertical eye opening (VEO) represents the height of the post-equalized eye, measured midway between the mean zero crossing of the eye. This position in time approximates the CDR sampling phase.
The resulting 64 × 64 matrix produced by the EOM can be processed by software and visualized in a number of ways. Two common ways to visualize this data are shown in Figure 7 and Figure 8. These diagrams depict examples of eye monitor plot implemented by software. The first plot is an example of using the EOM data to plot a basic eye using ASCII character, which can be useful for simple diagnostics software. The second plot shows the first derivative of the EOM data, revealing the density of hits and the actual waveforms and crossing that comprise the eye.