Casio CZ-1 Service Manual And Spare Parts List page 114

21-4.
VCO
(Voltage Controlled
Oscillator)
A- IN
*
A-OUT
BIN
BOUT
The
VCO
is
an
oscillator
whose
oscillation
frequency
varies in
accordance with the
input voltage
level.
In
the
left
figure,
the voltage
levels
of the
A-OUT
and
the
B-OUT
are opposite.
n
i
When A-OUT
is
HIGH, B-OUT
drops
to
LOW.
(2)
From A-OUT.
electric
current flows into B IN
via a
differentiation circuit.
As
a result,
the voltage of
B-IN drops
gradurily while
the A-IN voltage gradually
rises.
AIN
A-OUT
JUTTL
""LTLTLT
Threshold
"itvtl
CA
AOUT>H
h
7*
Thrtshold
Itvtl
CB
B
OUT>H
|-
A-IN
(3)
When
B-IN becomes lower than
the threshold level,
B-OUT
rises to
HIGH.
When
A-IN becomes
higher than the threshold
level,
A-OUT
drops to
LOW.
(4)
The
circuit oscillates repeating the
above
operations.
The
following
shows
the actual circuit of
VCO. When
control terminal
(a)
is
GND
(zero
volt),
it
takes
approximately
1
5 microseconds
for
the
differentiation circuit to
reach the threshold
voltage.