Figure 4-11. AC coupled timing measurements with Threshold DAC.
With the 3.3 ACV range selected, a 10% duty-cycle square wave with 5 V peak-to-peak value, presents a
peak-to-peak signal at the internal measuring circuits of –0.5 V to + 4.5 V. The AC Median Value is
+2.0 V. By setting the Threshold DAC to the Median value, the internal measuring circuits are properly
biased for best performance.
Figure 4-12. Comparator and Threshold DAC Settings
4.12.2 Frequency and Period Measurements
Both
Freq.
and
Per
check boxes are only visible when ACV or ACI functions are selected. These check boxes are
used to make frequency or period measurements.
Freq.
measures from 1 Hz to 300 kHz. When activated, the
ontrol panel alternately updates the amplitude reading followed by the frequency reading. The reading rate is
slow
y is activated. In the Windows control panel, period (
Per
) is also selectable.
a
c
er than indicated when frequenc
Once the frequency range is acquired, Frequency and Period have a maximum measurement time of about 1 second.
It could take up to five measurements before the correct frequency range is auto-selected. This process is automatic.
Once within range, the next frequency measurement is made at the last selected range.
Both Frequency and Period measurement performance can be improved by properly setting the Threshold DAC,
novel feature of the SMX2044. See “Threshold DAC”, “AC Median Value”, and “Peak-to-Peak” measurements for
further details.
37
Signametrics
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