51
Pulse and Pulse-trains
Pulse and pulse
−
trains are both selected and set
−
up from independent menus on the
STANDARD
WAVEFORMS
screen called by pressing the STD key. Pulse and pulse
−
trains have similar timing
set
−
ups and considerations but pulses are only unipolar, with a maximum amplitude of 10Vpp,
whereas pulse
−
trains can be bipolar, with a maximum peak
−
to
−
peak of 20Vpp.
Pulse Set-up
Pulse waveforms are turned on with the
pulse
soft
−
key on the
STANDARD WAVEFORMS
screen; pressing the
setup…
soft
−
key beside
pulse
calls the first of the pulse set
−
up
screens:
Enter pulse period:
100·0 us
◊
exit next
◊
The pulse period can be set between 100·0ns and 100s, with 4
−
digit resolution, by direct entries
from the keyboard or by using the rotary control. Pressing the
next
soft
−
key calls the pulse
width screen:
Enter pulse width:
program 50·00 us
(actual 50·00 us)
◊
exit next
◊
The width can be entered directly from the keyboard or by using the rotary control. Any value in
the range 25.00ns to 99·99s can be programmed but the
actual
value may differ because of
the considerations discussed below; for this reason the
actual
pulse width is shown (in
brackets) below the
program
width.
Pressing the
next
soft
−
key calls the pulse delay screen:
Enter pulse delay:
p0·000 ns
(0·000 ns)
◊
exit done
◊
This is very similar to the pulse width screen and, again, the
actual
delay is shown below
the
program
delay. The delay value that can be entered must be in the range ± (pulse period
−
1 point); positive values delay the pulse output with respect to waveform sync from SYNC OUT;
negative values cause the pulse to be output before the waveform sync. Pressing the
done
soft
−
key on this screen returns the display to the
STANDARD WAVEFORMS
screen.
The means by which pulse period is set
−
up in the hardware requires an understanding because it
affects the setting resolution of both pulse width and delay. Pulse is actually a particular form of
arbitrary waveform made up of between 4 and 50,000 points; each point has a minimum time of
25.00ns corresponding to the fastest clock frequency of 40MHz.
At short pulse periods, i.e. only a few points in the waveform, the setting resolution is, however,
much better than 25.00ns because the time
−
per
−
point is adjusted as well as the number of
points; since the pulse width and delay are also defined in terms of the same point time, varying
the time
−
per
−
point affects their resolution. For example, if the period is set to 500ns, the
minimum pulse width, when set to 25.00ns, will actually be 25.00ns; 20 points at 25.00ns each
exactly define the 500ns period. However, if the period is set to 499·0ns, 20 points at the
minimum point time of 25.00ns will be too long so 19 points are used and the point time is
adjusted to 26.26ns (499·0
÷
19); 26.26ns is now the increment size used when changing the
pulse width and delay.
