38 Source User’s Guide
Basic Digital Operation
Using Waveform Markers
Pulse/RF Blanking always occurs on the low part of the signal regardless of the
polarity setting.
Using the TRIGGER 2 Signal as a Transceiver Trigger
One of the uses for the TRIGGER 2 signal (marker signal) is to trigger a
measurement instrument. You can set up the markers to start the
measurement at the beginning of the waveform, at any single point in the
waveform, or on multiple points in the waveform. To optimize the use of the
TRIGGER 2 OUT signal for measurements, you may also need to adjust the
sample rate. To change the sample rate setting click Input/Output, RF Source,
Modulation Setup, ARB Setup, Sample Rate keys.
The TRIGGER 2 output signal can exhibit jitter of up to ±4 ns on the rising and
falling edge. This jitter can be minimized in either of two ways.
Method 1: Use a sample clock of 200 MHz/N where N is a positive integer and
where 200 MHz/N can be represented exactly on the display.
For example: 200 MHz, 100 MHz, 50 MHz, 25 MHz, and so on.
If the result cannot be represented exactly on the display, jitter will be present.
For example: N = 6 will result in jitter, because 200 MHz/6 = 33.333 Mhz,
which is truncated when displayed.
Method 2: Select a sample clock and waveform length that spaces the markers
by a multiple of 8 ns. For example: A 200 point waveform with a marker on the
first point and a sample clock of 50 MHz provides a marker every 4 µs. Because
4 µs is a multiple of 8 ns, the jitter is minimized.
When the TRIGGER 2 signal exhibits jitter and it is used as a measurement
trigger, it can cause the waveform to falsely appear as having jitter. If this
condition occurs, you can adjust the sample rate to a value (see above) that
does not cause the jitter appearance. To maintain the integrity of the original
waveform with a sample rate change, you will have to also recalculate the
sample values. The following figures illustrate the marker signal jitter and its
effect on the waveform.
The jitter is gone with
an optimal sample rate
Waveform appears to exhibit jitter when
triggered using EVENT signal with jitter.
Oscilloscope triggering on waveform
Oscilloscope triggering on EVENT signal
Oscilloscope triggering on EVENT signal
TRIGGER 2 signal exhibits jitter
due to a non-optimal sample rate
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