HP 54645A, User'S And Service Manual

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Viewing Signal Detail with Display Mode
Remember how you had to constantly adjust the brightness on old analog
scopes to see a desired level of detail in a signal, or to see the signal at all?
With the HP 54645A/D, this is not necessary. The HP 54645A/D brightness
knob operates much like the brightness knob on your computer screen, so
you should set it to a level that makes for comfortable viewing, given the
room lighting, and leave it there. Then you can control the “detail” by
selecting a Display Mode: Normal, Peak Detect, or Average, as described in
the following paragraphs.
Normal Mode
Normal mode is the display mode that you will probably use for acquired
samples most of the time. It compresses up to 1 million acquisition points per
channel into a 4,000-point display record with vectors off, or a 2,000-point
record with vectors on.
The scope’s 200 MSa/s sampling speed specification means that samples are
taken every 5 ns. At the faster sweep speeds, the running display is built from
many individual triggers. If you press the Stop key, and pan and zoom
through the waveform, only the last trigger’s acquisition will be displayed.
Whether the scope is stopped or running, you see more detail as you zoom in,
and less as you zoom out. To keep from losing detail as you zoom out, switch
to the Peak Detect display mode. “Zoom” means you expand the waveform
using either the main or delayed sweep window. “Panning” the waveform
means you use the Delay knob to move it horizontally.
Peak Detect Mode
In Peak Detect display mode, any noise, peak, or signal wider than 5 ns will
be displayed, regardless of sweep speed. In Normal display mode, at faster
than 2 us/div, you would see a 5-ns peak, so peak detect has no effect at
sweep speeds faster than 2 us/div. Note that in this case the Pk status
indicator on the top line of the display is not highlighted.
Using Peak Detect and Autostore together is a powerful way to find spurious
signals and glitches.
Average Mode
Averaging is a way to pull the signal out of noise. Averaging works better than
either a bandwidth limit or a brightness control because the bandwidth is not
reduced.
Front-Panel Overview
Important Oscilloscope Considerations
2-3