Keithley DAS-4300 Series, User Manual

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2-18 Functional Description
Random Interleave Sampling (RIS)
In addition to ETS, the DAS-4301/8K board provides Random Interleave
Sampling (RIS). Like ETS, RIS allows the DAS-4301/8K board to
sample a repetitive signal at rates above 1 Gsamples/s. Unlike ETS,
however, the signal does not have to be coherent with the pacer clock.
This feature is particularly convenient in scope-type applications where
you may not be overly concerned about the time it takes to complete the
acquisition but you want to watch the screen filling with data.
One advantage of RIS over ETS is the ability to acquire and display
pre-trigger data at sampling rates of up to 20 Gsamples/s. RIS also offers
more trigger source options than ETS. The trigger for the signal can be
derived from the signal (external software analog trigger), external
hardware analog trigger, or external digital trigger. If the trigger source is
external analog or digital, the trigger needs to be synchronized with the
signal.
RIS offers the same sampling rates as ETS: 2, 4, 5, 10, and
20 Gsamples/s. During each acquisition, an entire waveform is collected.
Ideally, at 20 Gsamples/s, 20 waveforms sampled at 1 Gsamples/s are
required to reconstruct a waveform equivalently sampled at
20 Gsamples/s. However, because the waveforms fall randomly, many
waveforms are usually required. The DAS-4300 scope and test program
updates the waveform as each is acquired.
Figure 2-5 illustrates how RIS works.