Datasheet

Application Note
www.tektronix.com/bench4
Preparing for Digital Acquisition
There are two basic tasks to prepare a MSO for digital
acquisition. First, just like a logic analyzer, the MSO digital
channel thresholds are configured for the logic family being
measured to ensure the correct logic level is acquired.
Secondly, the analog channel’s skews are adjusted for
accurate time correlation between the analog channels and
the digital channels.
The MSO’s analog channel is used to quickly check the logic
swing of your digital signal. In Figure 5, the MSO automatically
measures the 5 V CMOS signal amplitude with measurement
statistics across multiple acquisitions. For logic families with
symmetrical voltage swings like CMOS, the threshold is at
half of the signal amplitude. In Figure 6, the digital channel
threshold is set to 2.5 V which is half the amplitude of the 5 V
CMOS signal. However, for logic families with asymmetrical
voltage swings like TTL, you typically need to consult the
component data sheet and define the threshold as half-way
(TTL V
threshold
= 1.4V) between the logic device’s maximum low-
level input voltage (TTL V
IL
= 0.8V) and minimum
high-level input voltage (TTL V
IH
= 2.0V) values.
In Figure 6, you can see the timing skew between the rising
edges of the analog and digital waveforms of the same signal.
The analog waveform is leading the digital waveform. For
accurate measurements, it’s important to remove the analog
to digital time skew for better time-correlation measurements
between the analog and digital waveforms. The Tektronix
MSO Series provides adjustable analog probe deskew to
align the analog channels with each other and to align the
analog channels with the digital channels. The analog channel
deskew settings compensate for different analog probe
propagation delays.
Every Tektronix MSO Series oscilloscope is provided with a
logic probe. To simplify digital measurements, the oscilloscope
compensates for the propagation delay of the logic probe.
Therefore, there are no digital channel probe deskew
adjustments.
Figure 5. Quick verification of the 5 V CMOS signal amplitude using measurement
statistics.
Figure 6. Setting the MSO digital threshold to 2.5 V for a 5 V CMOS signal.