Hi. In this short video, I will show you how to use the jitter analysis and real-time eye
features on Keysight’s InfiniiVision 6000 X-Series oscilloscope. Let’s get started.
You can see here on the screen that there’s jitter on the clock edge. You can tell because
the edge appears to be bouncing around relative to the trigger point. This is referred to
as time interval error, which means that the edge is either occurring too early or too late
in relation to the sample point. This can cause sampling errors at the receiver of your device.
Many times with high-speed serial buses, the clock may not be explicit,
which means that it must be recovered at the receiver. We can use an oscilloscope to simulate
the receiver by using its clock recovery algorithm. Sometimes jitter may not be as
obvious, and so it’s important to use jitter analysis to uncover it. Let’s use the 6000 X-Series
jitter analysis to try and find the cause of this jitter.
We will first need to enable the jitter analysis and add a time interval error measurement that will be based
on a constant clock recovery. This will simulate a receiver with no filter. The auto-setup
keys make it easy to enable various jitter measurements, and each plot will be based
on timing errors of each edge of the signal relative to the recovered clock.
First we will enable the histogram. The bimodal distribution reveals deterministic jitter is affecting
the signal. Now let’s enable the jitter trend waveform.
The purple waveform is time-correlated to the captured signal. Notice that the jitter trend has a sinusoidal modulation, which indicates
that periodic jitter is affecting the signal. We can use the built-in measurements to determine
the frequency of the trend line. Using the 6000 X-Series jitter analysis feature revealed
that the jitter was periodic and had a frequency of about 100 KHz. The real-time eye
feature is another way to view the effects that the jitter has on the signal. We will
first acquire the real-time eye with a constant clock recovery which will simulate a receiver
with no filter. Under the Analyze menu, select Features, select Real Time Eye,
and we can make sure that the clock recovery is set to Constant Frequency.
Now press Acquire Real Time Eye. An eye diagram is an overlay of individual bits
based on the clock recovery. You could see here that the eye is closed which is due
to the edge shifts of each bit. We can also draw a box at the signal zero crossing and
enable the histogram to visualize the jitter distribution within the box.
An ideal eye diagram will be open, showing that there isn’t any significant jitter affecting the signal.
Another type of clock recovery used in high-speed serial buses is a phase-lock-loop bandwidth
filter, which can help to eliminate jitter. First and second order phase-lock-loop clock
recovery can be used to simulate this on the 6000 X-Series oscilloscope. Let’s change
the clock recovery to a PLL to try and filter out this jitter.
This particular signal has a speed of ten megabits per second. And from our first measurement, we determined the frequency
of the jitter was about 100kHz. We could set the bandwidth loop to 1.5 MHz
to ensure we have filtered out the sinusoidal jitter and all of its higher harmonics.
Now we will acquire the real time eye again.
As you can see, the eye has opened and is not
being affected by the jitter anymore. This histogram has a Gaussian distribution which
also tells us that we have successfully filtered out the jitter.
In this short video, we used the oscilloscope to simulate a receiver on a high-speed serial bus.
For more information on the Keysight InfiniiVision 6000 X-Series oscilloscope, please visit Keysight.com.
And, for a live demonstration, please contact your local Keysight representative. Thank you.