Wavetek 144 Instruction Manual page 17

3.1.2
Sweep Generator
and Trigger Logic
CONTINUOUS
MODE
In this
mode, both the
Main
Generator and the
Sweep
Generator operate independently.
As shown
in
Figure 3-3,
the
Sweep
Generator
is
a passive integrator
with
a
Voltage
Controlled Current Source.
The
output
of the
Sawtooth
Amplifier changes the
states
of
both the
Peak and Zero
Detectors
when
either
the
peak or the zero limit
is
reached,
thus switching
on and off
the current source output.
The
result
of this
charging
and
discharging of the
timing capaci-
tor
is
a
continuous
generation of
a
sawtooth waveform.
The
charging
and discharging rate
of the timing capacitor,
also
the repetition rate
of the
sawtooth waveform,
is
pro-
portional to
the
amount
of current fed
into
the capacitor
and the
size
of the capacitor.
The amount
of
current
output
is
proportional to the controlling voltage
and the
current
programming
resistor.
Thus, the repetition rate
is
controlled
by
the
sweep time
VARIABLE
control
R33
and the
SWEEP TIME
range
selector switch.
The Current Source Switch provides
a
shunt path
to signal
ground
for
the timing capacitor
when
the
sawtooth wave-
form
is
in
the negative slope
region.
Switching
action
is
activated
by
the
Peak Detector and the Zero Detector
outputs.
The
Sawtooth
Amplifier
is
a
noninverting, high
input
impedance, high slew rate
amplifier providing
low
output impedance and complete isolation for the passive
integrator.
The Peak and Zero
Detectors accomplish detection of both
extremes
of the
sawtooth waveform.
The
outputs of these
two
detectors,
in
conjunction with other transistor
switches,
causes the
Current Source Switch to place
a
shunt path
across the
Timing
Capacitor or
remove the shunt
path.
Thus, the operational loop
is
completed
for
the
Continuous
Mode
operation of the
Sweep
Generator.
TRIGGERED OR GATED
MODES
Refer to Figure 3-4. In
both the Triggered
and
the
Gated
modes,
the
Main Generator and the
Sweep Generator
operate independently.
Figure 3-3
—
Sweep
Generator,
Continuous
Mode
3-3