Datasheet

www.tektronix.com/bench 7
Digital Debugging Tips Using a Mixed Signal or Mixed Domain Oscilloscope
Figure 12. LVPECL signal zero with 50 ns period and signal one with 90 ns period.
Signal 0
Signal 1
2.4V
1.6V
2.4V
1.6V
Figure 13. MSO triggered on 727.3 ps glitch on the bottom LVPECL signal.
See the Complete Picture with Analog
and Digital Acquisition
In this example, two Low-Voltage Positive Emitter-Coupled
Logic (LVPECL) signals are verified. The 3.3 V LVPECL logic
high is approximately 2.4 V and the logic low is approximately
1.6 V. Therefore, the MSO digital channels thresholds are set
to 2.0 V.
Signal zero is a square wave with approximately 50 ns
period and signal one is a square wave with approximately
90 ns period as shown in Figure 12. There is no fixed time
relationship between the signals.
The same verification technique that was used in the previous
TTL burst example is used to verify these LVPECL signals. To
check for non-conforming signals, the MSO is configured to
trigger on a pulse width less than 22.4 ns. In Figure 13, the
MSO triggered on a 727.3 ps glitch on the bottom signal.
Capturing this glitch required the MSO to have a timing
resolution that is better than 727.3 ps.
An important MSO acquisition specification is the timing
resolution used for capturing digital signals. Acquiring a
signal with better timing resolution provides a more accurate
timing measurement of when the signal changes. For example,
a 500 MS/s acquisition rate has 2 ns timing resolution and
the acquired signal edge uncertainty is 2 ns. A smaller timing
resolution of 60.6 ps (16.5 GS/s) decreases the signal edge
uncertainty to 60.6 ps and captures faster changing signals.
The Tektronix MSO5000B, MSO4000B and MDO4000B
Series internally acquire digital signals with two types of
acquisitions at the same time. The first acquisition is with
timing resolution down to 2 ns for a record length up to 250
M. The second acquisition is called MagniVu
™
high speed
acquisition. The MagniVu timing resolution is down to 60.6 ps
with up to a 10,000 point record length acquisition centered
on the trigger. The MDO3000 Series provides MagniVu timing
resolution up to 121.2 ps. The MagniVu acquisition shows
signal transition details like glitches that are not seen by other
instruments with less timing resolution.
In Figure 13, the bottom signal glitch occurs at the same time
that the rising edge of the top signal occurred. This could be
a crosstalk problem but more information is needed before
making this diagnosis.