Datasheet

www.tektronix.com/bench 13
Digital Debugging Tips Using a Mixed Signal or Mixed Domain Oscilloscope
Figure 26 shows Wave Inspector searched for the maximum
ADC output value of 3F hex. Wave Inspector’s bus search
found 18 events. These events are gathered in three groups of
search marks which are located at the test ramp signal peaks.
But each peak has multiple 3F hex values and not just one 3F
hex value which should be at each test ramp signal peak.
Figure 27 shows the Wave Inspector right arrow navigation
key was used to jump from the trigger position in Figure 26
to the first marked 3F event to the right of the trigger. Notice
in the center of the MSO display, the ADC output bus data is
37, 38, 39, 3A, 3B, 3C, 3D, 3E and six 3Fs hex values. The
correct operation is one 3F hex value at the peak of the test
ramp signal.
A clipped top of the test ramp signal at the ADC input could
have produced multiple 3F hex values but the analog channel
ADC input waveform looks good; it’s not clipped or distorted
at the test ramp signal peak. Rather, the multiple 3F hex
values at the peak of the test ramp signal indicate that the
analog signal exceeded the maximum ADC input voltage.
The test ramp signal processed by the signal conditioning
exceeds the maximum ADC input voltage and the processed
signal does not reach the minimum ADC input voltage. To fix
this problem the acquisition system signal conditioning offset
and gain need to be adjusted. Notice the ADC input waveform
maximum is 1.871 V and the minimum is 854.1 mV on the
bottom left corner in Figure 27. The signal conditioning
circuit offset and gain needs to lower both these values for
correct operation.
Figure 26. Wave Inspector bus search finds too many 3F hex values at test signal
peaks.
Figure 27. Wave Inspector navigation jumps to marks at 3F hex values at test signal
peak