LMH0318_15 Datasheet, PDF (15/57 Pages) Texas Instruments – LMH0318 3 Gbps HD/SD SDI Reclocker with Integrated Cable Driver

www.ti.com
LMH0318
SNLS508 – SEPTEMBER 2015
Feature Description (continued)
8.3.3 2:1 Multiplexer
A 2:1 input multiplexor connects IN0 and IN1 to the CDR. By default, IN0 is selected. To select IN1, the 2:1
multiplexer must be set. See LMH0318 Programming Guide (SNLU183) for detailed settings.
8.3.4 Clock and Data Recovery
By default, the equalized data is fed into the CDR for clock and data recovery. The CDR consists of a reference-
less Phase Frequency Detector (PFD), Charge Pump (CP), Voltage Controlled Oscillator (VCO), and Output
Data Multiplexer (Mux).
The inputs to the Phase and Frequency Detector (PFD) are the data after the CTLE as well as I and Q clocks
from the VCO. The LMH0318 will attempt to lock to the incoming data by tuning the VCO to phase-lock to the
incoming data rate.
The supported data rates are listed in the following table. See LMH0318 Programming Guide (SNLU183) for
further information on configuring the LMH0318 for different data rates.
DATA RATE RANGE
2.97 Gbps, 2.967 Gbps
1.485 Gbps, 1.4835 Gbps
270 Mbps
125 Mbps
Table 1. Supported Data Rates
CDR MODE
Enabled
Enabled
Enabled
Disabled
COMMENT
At 125 Mbps device is in CDR bypass
8.3.5 Eye Opening Monitor (EOM)
The LMH0318 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 interval 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 20 and Figure 21. These diagrams depict
examples of an eye monitor plot implemented by software. The first plot is an example of using the EOM data to
plot a basic eye using ASCII characters, 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.
Copyright © 2015, Texas Instruments Incorporated
Product Folder Links: LMH0318
Submit Documentation Feedback
15