W h e n a C D is played back, L D / C D signal becomes L, the
A P C O signal is cut off by Q8, the V C X O frequency is fixed
at 8.4672MHz by the voltage set by VR3 while with an
L D D disc, this frequency becomes variable in the range
of 8 . 4 6 7 2 M H z ± 3 K H z .
T h e C D ' s spindle servo system negatively feeds the infor
m a t i o n of the d a t a quantity stocked in the player's R A M
back to the spindle-motor, and the quantity of stored data
in the R A M is kept within the range of ± 3 frames of the
average.
This is impossible with L D D disc because the L D spindle
m o t o r is controlled by H sync. As a substitute for the
above, L D D players takes the following m e t h o d .
W h e n the data in the R A M becomes smaller t h a n the aver
age by 3 frames, Z6 (TC9179F) D I V + signal shifts to H ,
Z l l - 3 shifts to H disregarding A P C O signal. This decreases
the V C X O ' s oscillating frequency and slows d o w n data
processing t o recover the average stored data quantity.
W h e n the d a t a quantity exceeds the average by 3 frames,
D I V - becomes H , Z l l - 3 shifts to L, V C X O frequency
increases, the processing speed is accelerated and the stored
d a t a decreases d o w n t o the average.
W h e n the quantity of the stored d a t a becomes n o r m a l
(average ± 2 frames), D I V
4 -
or D I V - shifts to L.
Z9 (SN74LS221N) 1/2, C D D M , is triggered and the Z7-17
A P C G signal shifts t o L temporarily. The A P C O signal
is fixed at the duty cycle of 5 0 % (0 phase difference) by
the low A P C G signal. After the V C X O frequency is
returned to its center value, a u t o m a t i c phase comparison
is resumed.
As mentioned, C D player generates 4.3218MHz clock
(PLCK) signal and synchronizes it with the suppressed pit-
repetition signal of the same frequency contained in the
reproduced E F M signal. The E F M signal contains some
signals close t o 4.3218MHz when the pickup is between
music pieces.
W h e n searching, P L L circuit opens and t h e reproduced
and generated signals become out of synchronization. If
the searching is terminated between music pieces, the os
cillation m a y mislock at a close signal to 4.3218MHz.
T h e C D system can not sense the frame sync in the mis-
locked period. So, F S P S (Frame sync pattern synchroni
zation) signal shifts to H , Z4 (TD6315AP)-11 shifts to L.
Z4-7&8 become high in impedance. C I 1 connected to Z4-4
holds the previous value and VCO frequency is fixed. In
this period the disc turns at a nonrated speed. W h e n the
reproduced pit-repetition frequency reaches the fixed V C O
frequency, frame sync is picked up and F S P S signal shifts
t o L and the P L L loop closes.
In L D D , resynchronization between the frame sync and
clock by F S P S is impossible because, as mentioned, the
r o t a t i o n of the spindle m o t o r is n o t controlled by P C M
signal. T o resynchronize them, Z10 blocks out the F S P S
signal when the L D / C D signal shifts to H . W h e n the
S E A R C H is terminated and the falling edge of S C A N sig
nal triggers Z 9 (2/2), Q5 closes and pulls the V C O input
to + 5V. T h e n the VCO frequency returns to 4 3 2 1 8 M H z .
LD-707 (NTSC) is also capable of reproducing digital
sound signal recorded o n L D D discs when combined with
a LaserVision Digital Sound Processor D A - 1 .
26
Fig. 5 Control Circuit of Reference Signal Frequency(CLD-900)
v c o
CD: The phase of 4 . 3 2 1 8 M H z ref clock varies t o
synchronize w i t h reproduced sync.
LDD: Spindle motor is free f r o m VCO.
V C X O
CD: Fixed t o 8 . 4 6 7 2 M H z
LDD: 8 . 4 6 7 2 M H z ± 3 k H z t o control digital signal
processing speed
