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Chapter 4 145
Basic Digital Operation
Triggering Waveforms
Triggering Waveforms
Triggering is available in both ARB and real-time formats. ARB triggering controls the playback of a
waveform file; real-time custom triggering controls the transmission of a data pattern. The examples and
discussions in this section use the dual ARB Player, but the functionality and methods of access (described
on
page 147 ) are similar in all ARB and real-time formats.
Triggers control data transmission by telling the ESG when to transmit the modulating signal. Depending on
the trigger settings, the data transmission may occur once, continuously, or the ESG may start and stop the
transmission repeatedly (Gated mode).
A trigger signal comprises both positive and negative signal transitions (states), which are also called high
and low periods; you can configure the ESG to trigger on either state. It is common to have multiple triggers,
also referred to as trigger occurrences or trigger events, occur when the signal generator requires only a
single trigger. In this situation, the ESG recognizes the first trigger event and ignores the rest.
When you select a trigger mode, you may lose the signal (carrier plus modulation) from the RF output until
you trigger the modulating signal. This is because the ESG sets the I and Q signals to zero volts prior to the
first trigger event, which suppresses the carrier. If you create a data pattern with the initial I and Q voltages
set to values other than zero, this does not occur. After the first trigger event, the signal’s final I and Q levels
determine whether you see the carrier signal or not (zero = no carrier, other values = visible carrier). At the
end of most data patterns, the final I and Q points are set to a value other than zero.
There are four parts to configuring a waveform trigger:
• Source determines how the ESG receives the trigger that initiates waveform play.
• Mode determines the waveform’s overall behavior when it plays.
• Response determines the specifics of how the waveform responds to a trigger.
• Polarity determines the state of the trigger to which the waveform responds (used only with an external
trigger source); you can set either negative, or positive.