Service
TP
~
+
+
U 21
13
U2/12
U219
U
2/5
U21
4
U212
Figure 8- 3-
5.
Timing
diagram in advance mode
Constant Duty Cycle Mode
When Constant
Duty
Cycle Mode
is
selected,
the
control
voltage
for
the
rep. rate generator's negative
current
source (U13a/
030)
is
also
routed
to
the
width
generator - thus changing
the
pulse
width
in
proportion
to
any frequency change. This
is
achieved
by
tapping
the
junction
voltage at R
112
/ R
113
and
routing
it
via U15,
S4a
/pins 8, 9,
R215
and
R51
to
U16a/
pin
2,
which
drives
the
positive
current
source U 16b/
068
of
the
width
generator.
The
duty
cycle
limits
vary according
to
which
frequency
range
is
selected, an
individual
description
for
each range being given in the
following.
In the
10M
Hz - 1 M Hz
frequency
range, the
duty
cycle
is
fixed
at
approx
imately
8 %.
This
is
achieved
by re-routing the
supply
voltage
(from
S2a
/
pin
3)
via
R198
/ R197
to
the
width
current
source -
instead
of
via
the
width
vernier R222. The
width
range switches
are
disabled and
the
width
is
solely
dependent
on
the
frequency
setting.
L
In the 1
MHz
-
.1
MHz
frequency
range,
the
duty
cycle can
be
selected
from
2.5 %
to
10
%_
The
supply
voltage
for
the
width
current
sou rce
is
routed
via
S2a
/pins
1,2
to
the
width
vern ier R222.
All
width
range switches
are
disabled, and
the
width
(duty
cycle)
is
determined
by
a
combination
of
the
fixed
width
ramp capacitor C59, the
width
vernier setting and the voltage derived
from
U15
/
pin
6.
In the
frequency
ranges . 1 MHz
to
10
kHz,
10
kHz
to
1
kHz,
and 1
kHz
to
10 Hz,
only
the
width
range switches S4b and S4c are enabled. Transistors
072
to
075
and the associated ramp capacitors
C60
to
C64
are
switched in
by
the
rate range switches S2c/d/e/
f.
8- 20
Model 214B
TRIGGER
WIDTH
START
Scans by ArtekMedia => 2009
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