Agilent Technologies 54621A User Manual page 136

MegaZoom Concepts and Oscilloscope Operation
Acquisition Modes
If you cannot acquire multiple triggers, you can still reduce noise and increase
resolution at slower sweep speeds by setting # Avgs to 1.
54620-series 54640-series
Sweep speed Sweep speed
≤
2 us/div 200 ns/div
5 us/div 1 us/div
20 us/div 5 us/div
100 us/div 20 us/div
500 us/div 100 us/div
Realtime Mode
In Realtime mode, the oscilloscope produces the waveform display from
samples collected during one trigger event. The sample rate for the
54620-series is 200 MSa/s for single channel or 100 MSa/s with channel pairs 1
and 2, 3 and 4, or pod 1 and pod 2 running. The sample rate for the 54640-series
is 2 GSa/s for single channel or 1 GSa/s with channel pairs 1 and 2, or pod 1 and
pod 2 running.
When less than 1000 samples can be collected in the time spanned by the screen,
a sophisticated reconstruction filter is used to fill in and enhance the waveform
display.
To accurately reproduce a sampled waveform, the sample rate should be at least
four times the highest frequency component of the waveform. If not, it is
possible for the reconstructed waveform to be distorted or aliased. Aliasing is
most commonly seen as jitter on fast edges.
When Realtime mode is off, the oscilloscope produces the waveform display
from samples collected from multiple triggers, when on fast sweep speeds. In
this case, the reconstruction filter is not used. When the trigger is stable, this
produces the highest fidelity waveform.
Realtime mode is only necessary at sweep speeds of 200 ns/div and faster for
the 54620-series and 2 µs/div and faster for the 54640-series, since on these
ranges <1000 samples can be collected on each trigger. While the effective
bandwidth of the channel is reduced slightly, Realtime mode produces a
complete waveform for each trigger.
Realtime can be turned on when any other acquisition mode is turned on. Use
Realtime to capture infrequent triggers, unstable triggers, or complex changing
waveforms, such as eye diagrams.
4-20
Bits of resolution
(# Avgs=1)
8
9
10
11
12