Acquiring and Displaying Waveforms
3–60
TDS 500D, TDS 600B, & TDS 700D User Manual
Figures 3–28, 3–29, and 3–30 illustrate how DPO acquisition mode differs from
the normal acquisition mode used by digital storage oscilloscopes. Note that
normal mode follows a “capture waveform–digitize waveform–update waveform
memory–display waveform” cycle. Normal mode misses short term deviations
occurring during the long dead times. Typical waveform capture rates are
50 waveforms per second.
DPO mode increases the waveform capture rate to up to 200,000 waveforms per
second (maximum waveform rate depends on oscilloscope model), updating the
waveform array many times between displays. This very fast capture rate greatly
increases the probability that runts, glitches, and other infrequent events will
accumulate in waveform memory. The oscilloscope then displays the waveform
at the normal display rate using variable or infinite persistence and adjustable or
automatic brightness. You can control how long the waveform persists on screen
by selecting variable persistence and setting a decay constant. To display only
the most recent acquisition, select No Persistence.
DPO adds intensity or gray scale information, like an analog oscilloscope, to
each point in the waveform array. The waveform array is a two dimensional array
of display pixels. Display pixel values are incremented each time they are written
by a waveform acquisition. Pixels may saturate or overflow if the database is not
reset soon enough. When saturation occurs is a function of the depth of the array
for each pixel, the trigger rate, and how stable or consistent the acquisition data
is. The more consistent the data, the more often a given data location will be
incremented and the sooner it will saturate. To set the depth of the waveform
array, see To Set the Accumulation Depth on page 3–64.
To turn on DPO mode, do one of the following steps:
1. Press the front-panel button DPO.
2. Press DISPLAY ➞ Settings (main) ➞ Display (pop-up) ➞ Mode (main).
Push Mode again to toggle to DPO mode.
3. Press SAVE/RECALL SETUP ➞ Recall Factory With DPO (main) ➞
OK Confirm DPO Init (side) to recall the DPO factory setup.
To turn DPO off, press DPO. Alternatively, press DISPLAY ➞ Set-
tings (main) ➞ Display (pop-up) ➞ Mode (main), and then press Mode again to
toggle to Normal mode.
Waveform Capture Rate
To Use DPO Mode
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