Wavetek 144 Instruction Manual page 18

Figure 3-4
—
Sweep
Generator, Triggered or Gated Modes
When
this
instrument
is
in
the
TRIG mode
and
ready,
the
Main Generator Diode Gate
is
switched
off by the
Trigger/Gate Control,
and
the
Timing
Capacitor
is
dis-
charged through the shunt
path.
When
a trigger signal
arrives at
the Trigger/Gate Control, the control
flip-flop
changes
the
state,
opening the Diode
Gate. Current flows
into the
Timing
Capacitor, allowing the passive
integrator
to generate a triangle
waveform.
The
control
flip-flop
is
reset
by the square wave from
the
Sync
Amplifier
when
the proper phase
triggers
the
flip-flop.
The
flip-flop
output,
in
conjunction with the
level-shift circuit, closes the Diode
Gate. Thus, the
single
cycle generation of
a selected
wave-
form
is
accomplished.
When
in
the
GATED
mode,
the output of the Trigger
Level Comparator/Squaring
circuit
is
coupled
directly to
the Trigger/Gate Control.
The
sequence of operation
is
the
same
as that
of the
TRIG
mode,
except
that
one
or
more
cycles are
generated for the duration of the
trigger
(gate) signal
applied to the
TRIG
IN connector.
SWEEP
MODES
In
the
SWEEP
modes
of operation,
a
third input (the
Sweep
Generator output)
is
added
to the
VCG
Amplifiers through
the
SWEEP WIDTH
control.
In
the
CONT
SWP
mode,
the
Sweep
Generator and the Main Generator
run continuously.
In
the
TRIG SWP
and
SWP HOLD
modes, the Main
Genera-
tor runs continuously
at the
frequency
set
by the frequency
controls
until a trigger or gate pulse appears
at
the
TRIG
IN
connector.
(a)
Continuous Sweep Mode
Refer to Figure
3-5. In the
CONT SWP
mode,
the basic
frequency of the Main
Generator
is
set
by
the
FREQ
3-4
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