In my daily lab work, I use instruments to measure different signal parameters. This gives me a good understanding of each parameter as well as the ability to uncover signal integrity issues. I know some of you lack this advantage because you don’t have access to highly sophisticated test and measurement instruments, and wind up spending extra time and money debugging and optimizing your systems.
Given the complexity of high speed design, it’s highly desirable to have an embedded eye opening monitor that allows you to examine the shape and health of incoming signal waveforms and conduct real-time eye measurements, regardless of the data pattern. Ideally, the eye monitor would be non-intrusive and able to operate remotely to reduce your customer’s service-related issues and repair costs.
To better serve you, TI has implemented an on-chip eye opening monitor (EOM) in its latest generation of 3G-SDI reclockers, including the LMH0366 and LMH0376 with eye monitor and 4:1 input mux. These EOMs are non-intrusive, data pattern independent, able to operate remotely, and best of all -- they allow you to incorporate value added features. Whether you’re designing digital video routers, distribution amplifiers, or video test equipment, you can apply the LMH0366 or LMH0376’s eye monitor feature a few different ways.
Figure 1: Typical application of LMH0366 SDI Reclocker.
Reconstruct the eye diagram
The EOM provides 64 x 64 cells that allow you to reconstruct the eye diagram. This enables you to calculate jitter, rise/fall time, overshoot/undershoot, and much more. The device moves the eye horizontally and vertically against a reference and measures the number of hits.
Figure 2: Raw data produced by the EOM data.
Figure 3: System waveform shows eye density hits, with different color weight given based on number of hits.
Figure 4: System eye hit derivative waveform shows eye density hits, and uses the rate of change to determine the eye diagram.
HEO and VEO measurements
In certain applications, it may be more desirable to quantify the eye opening either by horizontal eye opening (HEO) or vertical eye opening (VEO). You’ll want to use the HEO and VEO to show the units interval (UI) eye opening. HEO divided by 64 specifies the UI eye opening, while VEO multiplied by a 3.125 mV range setting provides the vertical eye opening. These measurements provide a clear indication of signal quality.
EOM degradation interrupt
There are times when you’ll find it’s critical to set an interrupt due to the EOM going beyond a certain limit, or the reclocker loses lock, or you’ve lost the signal. The LMH0366 and LMH0376 reclockers have these capabilities. Under user control, a threshold can be set for the EOM and this will send an interrupt to the processor or microcontroller.
With lots of customer feedback, we developed these features to enhance your next broadcast video equipment design. As always, I’d very much like to hear from you. Please send your comments and suggestions. You can also ask questions and get answers in TI’s High Speed Interface Forum.