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5-6
SPINDLE
AND
TANGENTIAL
SERVO
].
General Outline
By comparing
the phase of a reference signal
with the phase of the synchronizing signal separa-
ted from the video signal reproduced from the disc.
the spindle servo maintains the spindle motor rpm
at a constant
value.
However,
due
to
the disc
eceentricity
and
track
irregularities,
time
base
errors of ЗО изр-р are generated in the reproduced
video signal, resulting in failure to obtain normal
color
in the reproduced
picture (since the errors
exceed
the
TV
receiver
color lock
rangel.
It is
therefore.
necessary
to
suppress
the
time
base
errors to a level not exceeding 20 изр-р, and this is
achieved by comparing the phase of the reproduced
color burst with the phase of a reference oscillation
signal. and sub-sequently driving a tangential mirror
to control
tangential
movement
of the laser
beam.
For this purpose,
the following
3 ICs are
employed.
i11 Control pulse generator IC (UMS5003)
(2) Tangential servo IC (12М3001)
(3) Spindle servo IC (UM8002)
the
У.
ЕС
COMP
SYNC =
LOCK
и
zm
А69
РЯ-8210-А
2.
Control Pulse Generator Circuit
Іп order
io generate
pulses required
for the
tangential servo and spindle servo. this IC includes
(1) burst gate. limiter and polarity inverter,
(2) reference
signal
generator
and
frequency
divider circuits,
(3) Equalizing pulse eliminator cireuit, and
i4) Sampling pulse generator.
And the block diagram is shown in Fig. 17.
2-a Burst gate, limiter and polarity inverter
When
the video signal is passed via C403 and
applied to pin 5. a burst signal output is obtained
from
pin 3. Noise
components
in the signal are
removed
by the
3.58MHz tuning circuit, and the
burst
signal output
from pin 3 is applied to the
limiter where
the signal js subjected to waveform
shaping.
Since
the burst
signal phase
is inverted
every H period, the phase is made uniform at every
H period by the polarity inverter, thereby forming
the sampling pulse signal for the tangential servo
phase comparator.
G A T E
F
SAMPLING
+
358;
САТЕ FOR
PULSE
i
rh — tuning
e
I
ج
фа
+
!
FON
- P
|
PBH
-
—
PULSE
GE
Fig. 17
Contro!
pulse generator circuit
ВЕРН
2401, 2402
0402-0406
17727
t
Sw
PULSE
В
256
GEN
о
—
T
|
т
---
tg
21
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