Teledyne LeCroy PXA125 - Manual (Page 24)

User Manual PXA125
1-10 Portrayal
Triggered Mode
In triggered mode, the PXA125 circuits are armed to generate one
output waveform. The trigger circuit is sensitive to transitions at the
trigger input. Select between positive or negative transitions to trigger
the instrument. When triggered, the generator outputs one waveform
cycle and remains idle at the first point of the waveform. The
instrument can be armed to receive a trigger signal from either the
front panel connector, soft command, an internal trigger generator,
from one of 8 backplane trigger lines or from a backplane STAR line.
As an alternative to an external source, the PXA125 has a built-in
trigger generator that can be programmed through a wide range of
frequencies and with 7 digits of resolution.
The trigger signal, whether it comes from the front panel, backplane
or from a soft command, has to pass through some electrical circuits.
These circuits cause small delay known as system delay. System
delay cannot be eliminated completely and must be considered when
applying a trigger signal. It defines how long it will take from a valid
trigger edge to the moment that the output reacts.
Gated Mode
In gated mode, the PXA125 circuits are armed to generate output
waveforms as long as a gating signal is present. Unlike the triggered
mode, the gated mode is level sensitive. When the gating signal goes
low, the waveform at the output connector is first completed and the
output reverts to an idle state. The idle amplitude level, after the
gating signal goes low, is the last point on the waveform.
Burst Mode
The burst mode is an extension of the triggered mode where the
generator can be programmed to output a pre-determined number of
waveforms. The sources to trigger a burst are the same as for the
trigger mode.
Frequency Agility
Using the latest DDS (direct digital synthesis) technology, the
PXA125 is extremely agile. Operations like sweep, FSK and FM are
directly derived from the DDS circuit by controlling its input bits.
Frequency agility is described below.