Keysight E8663D, Руководство пользователя

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126 Keysight E8357D/67D & E8663D PSG User’s Guide
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 method of access
(described on page 128 ) are similar in all (ARB and real–time) formats.
Triggers control data transmission by telling the PSG when to transmit the
modulating signal. Depending on the trigger settings, the data transmission
may occur once, continuously, or the PSG 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 PSG
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 PSG 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 PSG 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 PSG 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.