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IN connector.
The
VCG
Summing
Amp
is
an
inverting
amplifier
whose
output
voltage
is
used
to
control
a
positive
current source
and
a
negative current source.
For sym-
metrical
output waveforms,
the currents
from
the
two
current sources
are
equal
and
directly
proportional
to
the
voltage of the
VCG
Summing
Amplifier output.
The
Diode
Gate,
which
is
controlled
by
the
Hysteresis Switch,
is
used
to switch the
positive
current or the negative current to
the timing capacitor
selected
by
the
FREQ HZ
selector.
If
the
positive
current
is
switched
into
the timing
capacitor,
die voltage across the capacitor
will
rise
iinearly
to
generate
the
triangle
rise
transition,
if
the current
Is
negative,
the
voltage across the timing capacitor
will
fall
linearly
to
produce
the
fall
transition.
The
Triangle
Amplifier
is
a
unity
gain amplifier
whose
out-
put
is
fed to the Hysteresis
Switch
as well as
to the Sine
Converter.
The
Hysteresis
Switch has
two
voltage
limit
points (-M.25
V
and
-1.25
V).
During the time
the
output
voltage of the Triangle
Ampli-
fier
is
rising,
the
output
voltage of the Hysteresis
Switch
is
positive.
But
when
the
output
voltage
of the Triangle
Amplifier reaches
-t-1.25
V,
it
triggers
the Hysteresis
Switch
causing the switch
output
to
go
negative.
Once
the
control
+2.5V
I—
C
-2.5V
L_^_l
Figure 3-2
-
Simplified
Timing Diagram
voltage
into
the
Diode Gate becomes
negative,
it
will
switch die
positive
current out
and
switch the negative
current
in
to the
timing
capacitor, so that
the voltage
across
the capacitor
will reverse, starting a linear
decrease
of the
waveform.
When
the decreasing
voltage reaches
—1.25
V,
the
output
of the Hysteresis
Switch
will
switch
back
to
positive,
reversing
the
process.
This
action generates the
triangle
waveform
as
shown
in
Figure
3-2.
Since the
output
of the Hysteresis
Switch
is
a
square wave, the
result
is
simultaneous generation of
a
square
wave and
a
triangle
wave
at
the
same
frequency.
The
output frequency
is
determined
by
the
magnitude
of
the capacitor selected
by
the
FREQ HZ
selector
and
the
magnitude
of the
positive
and
negative current sources.
Since the current sources
are
linearly
proportional
to the
control voltage of the
VCG
circuit,
the
output frequency
will
also
be
linearly
proportional to the control
voltage.
If
the current of the negative current source
is
decreased
by 19
times,
the
fall
time
of the
triangle
will
be 19 times
longer
than the
rise
time of the
triangle; resulting
in
an
unsymmetrical
waveform
and
a division
of the
frequency
by
a
factor of
10.
Gradually
increasing
the current
from
the negative current source
and
decreasing the current
from
the
positive
current source
in
such
a
way
that
the
period for the
triangie
to
compiete one
cycle
remains
constant, the
symmetry
of the
output
waveform
can be
continuously
varied
while the frequency
is
held constant.
The
inverted
output
of the Hysteresis
Switch
is
fed to the
Sync
Amplifier
and
also
the
Square
Wave
Amplifier.
The
Square
Wave
Amplifier
cons;ists
of a
shaping
circuit
which
iimits
the
output swing
to
±1.25
volts.
For
positive
pulse outputs,
it
limits
the
output
voltage
swing
from
—1.25
V
to
0 V; and
for negative pulse
outputs,
it
limits
the
output swing
from 0
V
to +1
.25
V.
The
output
signai
from
the Triangle
Amplifier
is
applied
to the
Sine Converter, consisting of a
sine
shaping
circuit
and
a
sine amplifier.
The
sine,
triangle,
square,
positive
pulse,
or negative
pulse
is
fed to the
Output
Amplifier through
the
WAVE-
FORM
SELECTOR
switch
and
the
30
V
P-P
MAX
control.
The Output
Amplifier
is
an
inverting amplifier
whose
output
is
fed
into
a
step
attenuator
and
then
to
the
output
BNC
connector.
The
Attenuator
consists
of four
pi
attenuators,
each having
a
50-ohm
input
impedance
and
a
50-ohm
output imped-
ance.
There
is
one
—10
dB
attenuator,
one
—20
dB
attenuator,
and
two
—30
dB
attenuators.
By
combining
them
in
six
different
arrangements,
these
four attenuators
provide
10
dB
steps
of attenuation;
from 0
dB
to
—
60dB.
3-2
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