R101.
Therefore, the
voltage drop across R116
would be
equal to the voltage drop across
R101. Thus, amplifier
ICS is
operated as a voltage level
shifter
to shift the
voltage
referenced from
ground
to a voltage referenced
from
+15 volts.
Due to the
feedback control
of
amplifier
IC5, the voltage
drop across
R135 would be equal
to the voltage
drop
across
R116 which in turn is
equal to the voltage
output
of
amplifier
IC2. Since
the positive current
output from
Q24 is directly
proportional
to the voltage
across R135,
it
must also
be proportional to the
control voltage
of the
VCG amplifier.
Amplifiers
IC4 and IC6 are very
similar
to amplifiers
ICS
and
IC5 except
that
IC3 is an inverting amplifier
and IC4
is
a non-inverting
amplifier. If all
the 1 kJ2 resistors
in
Figure 3-3
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
across
R116 and
R135 will be reduced to
1/19th of
what it had been. Therefore,
the
output current
(1+)
will
be 1/19th the
negative current (I—).
In this
condition,
a nonsymmetrical triangle
with
a rise
to
fall
ratio of
19 to
1 and a frequency
of 1/1 0th the original
frequency
(symmetrical
frequency)
is generated.
If the
resistance
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,
R
135 and R 140
are
1 kS2
resistors.
Changing
the
FREQ
HZ multiplier
is
accomplished
by changing
the timing
capacitors
connected
to the
diode
gate.
For
frequency ranges below
X10,
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 IC5 and
ICS can not
be
neglected.
Therefore,
a high impedance buffer
amplifier
Q26 and
Q27 is inserted between
Q24 and
IC5, and another
buffer
amplifier
Q28 and
Q29 is inserted between
Q25and
the negative
input of
ICS.
Q27 is
connected
as
a
constant
current source supplying
the
bias current
to
Q2S
and minimizing
the change of
Vgs
of
Q26 with
temperature change. R129 provides
dc
offset
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
the
negative
input of
IC2, permitting
frequency
adjust-
ments
at the
minimum
setting
of the FREQ
DIAL. The
100
kl2
potentiometers
associated with
IC3,
IC4, IC5,
and
IC6 are
used
to
zero
offset
the
input terminal of
the
corresponding
amplifiers.
3.2.2
Triangle
Amplifier
The
Triangle Amplifier
consists of transistor
Q1
through
Q8,
with
Q1 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 level of
Q6. The overall Triangle
Ampli-
fier is
a unity gain amplifier
with very low output
imped-
ance.
3.2.3
Hysteresis
Switch
The Hysteresis
Switch consists
of
a comparator and a
flip-flop.
The integrated
circuit IC1 (CA3049) is
the
comparator, consisting of two
differential amplifiers. One
side of each differential
amplifier, pin
7 and pin
10,
are
connected
to
ground
through 22 ohm resistors.
Poten-
tiometers
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
con-
nected to pin 1 of
IC1 will
be conducting,
and the
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
CR13,
reversing
the
state
of
the flip-flop.
There
are three
RC networks
connected
to pin
1 and
three
RC networks
connected
to pin 4 of
IC1. These
six
RC
networks
provide frequency
response
compensation for
IC1 and
the
entire loop of
the Triangle
Generator
so that
it will
have
a
flat
frequency
response
from
dc to 10 MHz.
The flip-flop
is comprised of
transistors
Q10 through
Q16,
with
Q12 and Q13
connected
as a
differential
pair. Q14
supplies
a constant
bias
to
the
differential
pair,
preventing
saturation
during
their "on"
state.
Q11
and Q16
are
3-4
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