Datasheet

www.tektronix.com/bench 5
Digital Debugging Tips Using a Mixed Signal or Mixed Domain Oscilloscope
To align the analog channels with the digital channels, the 2.5
V position on the CMOS analog waveforms are time aligned
with the CMOS logic transitions which occur at the 2.5 V
threshold. As shown in Figure 7, a -1.60 ns deskew is used
to align the analog channel to the digital channel. This deskew
process is repeated for the other analog channels.
The analog channels skews should be checked when the
analog probes are changed and the digital thresholds should
be checked when measuring a different logic family. With
the threshold and skews configured, the MSO is ready for
verifying and debugging digital circuits. Next, several examples
of verifying a design using an MSO will be discussed.
Triggering on the Unexpected
The first example is verifying a TTL burst signal that contains
eight positive pulses as shown in Figure 8. The positive pulse
width specification range is 23.2 ns to 25 ns with 26 ns to 27
ns between the pulses. The time between the bursts is not
specified.
The MSO digital channel is connected to the TTL burst signal
and the threshold is set for TTL logic. The MSO is configured
for rising edge trigger. To speed up the verification process,
the MSO is configured to automatically measure the positive
and the negative pulse widths between the cursors.
Figure 9 shows a single shot acquisition where the MSO
triggered on the first pulse edge. Depending upon when the
MSO single shot acquisition button was pushed, the MSO
could have triggered on any of the other rising edges.
The acquired signal has eight pulses which comply with the
specification. The first positive pulse width is 23.88 ns and
the negative pulse width is 26.18 ns which are automatically
measured. These values are within the specifications. The
Tektronix MSO Series oscilloscope’s cursors are linked and
one control moves both cursors down the waveform checking
each positive and negative pulse width. All pulses in this
acquisition meet the specification.
Figure 7. Analog channel time aligned with the digital channel.
Figure 9. TTL Burst Signal.
Figure 8. TTL Burst Signal.
Unspecified time
between bursts