Application Examples
Low Duty Cycle Pulse Trains
15
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Using this technique the duty cycle range is limited to that achievable with the symmetry
control (99:1). For very small duty cycles, at lower repetition rates, the triggering
facilities may be used, as described in the next section.
Low Duty Cycle Pulse Trains
Low duty cycle pulse trains can be created by using the internal trigger generator to
produce the long interval between the pulses, with each pulse being a single cycle of the
main generator.
Set the main generator to 10 kHz by pressing
FREQ
,
1
,
0
,
kHz
, and reduce the duty-
cycle to 1:99 (i.e. pulse width of 1 µs) by pressing
SYMMETRY
,
1
,
%
.
Select the trigger menu by pressing
EDIT
,
TRIG
, and set
SOURCE=TGEN
, i.e. internal
trigger generator. The
TGEN
period should be at its default setting of 1.00 ms
(1.000 kHz) and the burst count set to 0001.
The default phase setting of 0 ° corresponds to the top of the rising edge of the pulse and
starting at this phase will not give the desired result; set the phase to -90 ° by moving the
cursor to the
PHASE
field with the
FIELD
keys and enter
-
,
9
,
0
,
ENTER
.
Whilst still in the trigger menu press
TRIG
again to turn Trigger mode on.
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A single cycle of the main generator (i.e. a single pulse) will now be output at the default
frequency of 1 kHz, so a 1000:1 duty cycle has now been achieved. Move the cursor to
the
TGEN
period field with the
FIELD
keys and increase the period using the rotary
control; although it will be difficult to see on the oscilloscope, the 1 µs pulse width is
maintained down to milliHertz repetition rates, i.e. an extremely small duty-cycle.
Note that at main generator frequencies above 30 kHz phase control of pulse waveforms
is restricted unless waveform generation is in low frequency mode (see
Waveform
generation options
in chapter 5,
Main Generator Operation
); this ultimately limits the
minimum width of pulses at very low repetition rates.
15-3
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.com
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