34
Trigger Edge
The
slope
soft
−
key is used to select the edge (
positive
or
negative
) of the external
trigger signal that is used to initiate a burst. The default setting of
positive
should be used
for triggering by the Internal Trigger Generator or an adjacent channel’s Trigger Out.
Note that the
trigger
signal from SYNC OUT, used for synchronising the display of a
triggered burst on an oscilloscope for example, is always positive
−
going at the start of the burst.
Burst Count
The number of complete cycles in each burst following the trigger is set from the
TRIGGER/GATE SETUP
screen called by pressing
setup
on the
MODE
screen.
TRIGGER/GATE SETUP:
♦
burst cnt: 0000001
◊
phase: +000.0º
(actual: +000.0º)
The required count can be set by pressing the
burst cnt
soft
−
key followed by direct entries
from the keyboard or by using the rotary control. The maximum number of waveform cycles that
can be counted is 1048575 (2
20
−
1).
Start Phase
The start phase, i.e. the point on the waveform cycle at which the burst starts, can be selected by
pressing the
phase
soft
−
key followed by direct entries from the keyboard or by using the rotary
control. Since the waveform cycle is always completed at the end of the burst the start phase is
also the stop phase.
The phase can be set with a precision of 0.1
°
but the actual resolution is limited with some
waveforms and at certain waveform frequencies as detailed below. To indicate when this is the
case the actual phase is shown in brackets as a non
−
editable field below the programmed value.
To achieve start phase precision all waveforms are run in Clock Synthesis mode, i.e. as if they
were arbitrary waveforms, when Triggered Burst is specified; this limits actual frequency
resolution to 4 digits for all waveforms although the normally DDS generated waveforms are still
entered with 7
−
digit precision. Sine/cosine/haversine/etc. waveforms are created as if they were
arbitrary waveforms with the first point of the waveform exactly at the start phase; each time the
phase or frequency is changed the waveform is recalculated which can cause a slight lag if these
parameters are being changed quickly with the rotary knob.
The phase resolution of true arbitrary waveforms is limited by the waveform length since the
maximum resolution is 1 clock; thus waveforms with a length >3600 points will have a resolution
of 0.1
°
but below this number of points the maximum resolution becomes 360
°
÷
number of
points.
Square waves, pulse, pulse trains and sequences have no start phase adjustment; phase is fixed
at 0
°
. A summary of start phase capabilities in Triggered Burst mode is shown in the table below:
Waveform
Max Wfm Freq
Phase Control Range & Resolution
Sine, cosine, haversine, havercosine 1MHz
± 360
°
, 0.1
°
Square
1MHz
0
°
only
Triangle
100kHz
± 360
°
, 0.1
°
Ramp
100kHz
± 360
°
, 0.1
°
Sin(x)/x
100kHz
± 360
°
, 0.1
°
Pulse & Pulse Train
10MHz
0
°
only
Arbitrary
40MS/s clock
± 360
°
, 300
÷
length or 0.1
°
Sequence
40MS/s clock
0
°
only
