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cvnplifier
whose
output
voltage
will
change between
0
and
—
S
volts
under normal
operating conditions. Transistor
Q21
limits
the
output swing
to
0 and
—7
volts.
The
output
of
IC2
is
usec(
to
control
both the
positive
and
negative
ojrrent
sources,
ICS through
ICG.
The
negative
input of
tCS
is
held at
0
volts
by
its
feedback.
The
current
through
R101 would
be
directly
proportional
to the
output
voltage
of IC2
if all
the source currents of
ICS and ICS
are neglected,
and
the current
through
R116
would
be
equal to the current
through
R101.
Therefore,
the voltage
drop
across
R1
16
would
be
equal to the voltage
drop
across
R101.
Thus,
amplifier
ICS
is
operated
as a
voltage
levd
shifter
to
diift
the voltage referenced
from
^ound
to a voltage referenced
from +15
volts.
Due
to the feedback control of
amplifier IC5, the voltage
drop
across
R1^
would be
equal to the voltage
drop
across
R1
16 which
in
turn
is
equal to the voltage
output
of
amplifier 1C2. Since
the
positive
current
output from
Q24
is
cttrectfy
proportional to the voltage across
R135,
it
must
also
be
proportion^
to the
control voltage of
the
VCG
amplifier.
Ampidiers 1C4 and IC6
are
very
similar
to amplifiers
ICS
»id IC5 except
that
IC3
is
an
inverting »nptifier
and IC4
is
a
non-inverting
amplifier.
If
all
the
1
kH
resistors
in
Figure
3^
are
well matched, the
positive
output
current
(1+)
and
the
negative
output
current
(I—)
will
be
equal
and
directly
proportional to the control
voltage.
These
two
currents are
alternately
switched
into a
timing capa-
citor
to generate
a
triangle
waveform.
By
increasing
the
resistance
of
R101
by
19
times,
the
voltage
drop acrbs
R116
and
R135
will
be reduced
to
1/19th of
u4rat
it
had
been. Therefore, the
output
current
(1+)
will
be
1/19di the negative current
(I—).
In
this
condition, a
non^mmetrical
triangle
with
a
rise
to
fall
ratio
of
19
to
1
and
a frequ»icy of
1/1
0th the
original
fre-
quency
(symmetrical frequency)
is
generated,
if
the
resis-
tance of
R101
is
decreased
and
the
resistance
of
R110
is
increased
by
exactly
the
same amount,
the
symmetry
ratio
will
be
gradually
changed
while the
output frequency
remains
constant.
Dual
potentiometers
R99
and
R103
provide
this
SYMMETRY
control.
For
FREQ HZ
multipliers
of
X10
to
X1M, R135
and
R140
are
1
k£2
resistors.
Changing
the
FREQ HZ
multiplier
is
accomplished
by
changing
the
timing
capacitors con-
nected to the
diode
gate.
For frequency
ranges
below
XI
0,
R135
and
R140
are
changed
instead
of changing the timing
capacitors.
In this
case,
the current
from
the current sources
will
go
as
low
as
50
nA, and
the source current of
ICS and IC6
can not
be
neglected.
Therefore, a high
impedance
buffer ampli-
fier
Q26
and
Q27
is
inserted
between
Q24
and
the negative
input of ICS,
and another
buffer amplifier
Q28
and
Q29
is
inserted
between
Q25
and
the negative input of
IC6.
Q27
'is
connected
as a
constant current source supplying
the
bias
current to
Q26
and
minimizing
the
change
of
Vgs
of
Q26
with temperature change.
R129
provides
dc
off^t adjustment
of the
buffer
amplifier.
Q28
and
Q29
function exactly
like
Q26
and Q27.
Refer to the
Main Board
schematic diagram
142-210
at
the
rear
of
this
manual.
FREQ
DIAL
control
R82
controls
the
amount
of current
supplied to
the
summing node
of the
VCG
amplifier,
thus
controlling
the
output
frequency.
VERNIER
control
R90
provides
fine
frequency
control.
R93
is
the zero adjustment
for the negative
input of
IC2,
so the
VCG
input terminal
is
not dependent
on
source
impedance.
R87
provides source current
compensation
for
die negative input of IC2, permitting
frequency
adjust-
ments
at
the
minimum
setting
of die
FREQ
DIAL. The
100
k£2
potentiometers
associated
with
ICS, IC4, ICS,
and
ICG
are
used to zero
offset
the input terminal of the
corresponding
amplifiers.
Q21
and
R100
are
used
to
limit
the
output
voltage
swing of the
VCG
amplifier,
IC2, to
+0.7
volts
and —7.0
volts.
TRIANGLE
AMPLIFIER
The
Triangle Amplifier
consists
of
transistors
Q1
through
Q8,
with
Qt
and
Q2
forming
a
very high input
impedance
differential
pair.
Q3
and
Q4
supply constant
bias
currents
to the
differential
pair,
increasing
the
open
loop
gain
of
the
amplifier.
Q5
is
connected
as a 7-volt
zener diode to
shift
the
output
tevei
of
Q6.
The
overall
Triangle Amplifier
is
a
unity gain
amplifier
with very
low output impedance.
HYSTERESIS SWITCH
The
Hysteresis
Switch
consists
of a
comparator and
a
flip-
flop.
The
integrated circuit IC1
(CA3049)
is
the
compara-
tor,
consisting
of
two
differential amplifiers.
One
side
of
each
differential amplifier,
pin
7
and
pin
1
0,
are
connected
tp
ground through
22
ohm
resistors.
Potentiometers
R23
and
R12
establish
the high
and low
voltage
limits
for the
comparator.
When
the
output
of the
Triangle Amplifier
reaches
+1.25 V,
the
transistor
connected to
pin
1
of
IC1
will
be conducting,
and
die
collector
current
through
pin
12
will
be
large
enough
to
turn
on
the tunnel diode
CR11,
which
in
turn
changes
the
state
of the
flip-flop.
When
the
output
of the Triangle Amplifier reaches
—1.25
volts,
the
transistor
connected
to pin
7 of
IC1
conducts and
its
collector
current at pin
6
will
be
large
enough
to turn
on
tunnel diode
CRTS,
reversing
the
state
of
the
flip-flop.
3-7
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