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Triggered Burst and Gate
Triggered Burst 7
7-5
Start Phase
The start phase, i.e. the point on the waveform cy
cle 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
so
me 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 the
frequency resolution to 8 digits for all waveforms although the normally DDS generated
waveforms are still entered with 10 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. This can cause a slight lag if the parameters are changed quickly using the
rotary knob.
The phase resolution of true arbitrary waveforms is li
mited by the waveform length since
the maximum resolution is 1 clock; thus waveforms with a length greater than 3600
points will have a resolution of 0·1 ° but below this number of points the maximum
resolution becomes 360 ° divided by the number of points.
Square waves, pulses, pulse trains and sequences have no start phase adjust
ment; phase is
fixed at 0 °.
A summary of start phase capabilities in triggered burst mode is shown in the table
below:
Waveform
Max waveform frequency Phase control range, resolution
Sine, cosine, haversine
and havercosine
2·5 MHz
±360 °, 0·1 °
Square 2·5 MHz 0 ° only
Triangle 500 kHz ±360 °, 0·1 °
Ramp 500 kHz ±360 °, 0·1 °
Sin(x)/x 500 kHz ±360 °, 0·1 °
Pulse and pulse train 25 MHz 0 ° only
Arbitrary 100 Msamples/s clock ±360 °, 360 ÷ length or 0·1 °
Sequence 100 Msamples/s clock 0 ° only
Manual Initialization of Inter-Channel Triggering
If a multi-channel instrument is set up such that all channels are triggered by
an adjacent
one it is possible to have a stable condition where all channels are waiting for a trigger
and the sequence of triggered bursts never starts. To overcome this problem any channel
can be triggered manually and independently using the force soft-key on that
channel’s TRIGGER IN screen. Select the channel to start the sequence with the
appropriate SETUP key, select the TR
IGGER IN screen with the TRIG IN key and
press the force soft key.
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