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DP-1100B II
5 - 2 - 2 T r a c k i n g Error Detection
T r a c k i n g error is a d e v i a t i o n of the r e a d i n g light s p o t f r o m the
pits (track) t o be t r a c e d .
In the
Pickup a m e t h o d
a d o p t e d t o d e t e c t t h e s p o t d e v i a t i o n f r o m a pit.
T h e h e t e r o d y n e s y s t e m is based u p o n the distribution of the
reflected light d i f f r a c t e d f r o m a pit d e p e n d s u p o n a relative
l o c a t i o n of t h e pit a n d s p o t .
5 - 3
R F S I G N A L
A RF signal is a s u m of e a c h electrical signal A
d e v e l o p e d b y the 4 - d i v i d e d p h o t o d i o d e (refer to 3 - 5 ) . T h e RF
signal is t h e n p r o c e s s e d t o provide EFM signal. T h e EFM
signal is t h e n c o n v e r t e d into an a n a l o g signal in passing
t h r o u g h a D-A c o n v e r t o r after d e m o d u l a t e d .
5 - 4
L I G H T E M I S S I O N F R O M L A S E R D I O D E
W h e n
the
LDC g o e s
b e c o m e s positive as s h o w n in the s c h e m a t i c d i a g r a m , A n d a
c u r r e n t f l o w i n g
t h r o u g h
Q 1 0 9 c u t off, t h e r e b y stops the oscillation of the Laser D i o d e .
3 0
II. FUNDAMENTALS
called
" h e t e r o d y n e
s y s t e m "
Fig. 5 . 5
P I C K U P Radial Signal Sampling T h e o r y (Pit depth X/4)
, A
, A
x
2
3
H, the
o u t p u t of
T A 7 5 4 5 8 ( Q 1 0 8 )
R 1 4 5 ,
D 1 0 2 ,
A n d
D 1 0 4
In this
s y s t e m ,
4 - d i v i d e d p h o t o d i o d e is a s s u m e d as A
a n d A
A
+ A
t
3
2
is
a n d A
A
+ A
t
3
2
established, w h i l e phase difference will be c a u s e d w h e n the
s p o t deviates f r o m a pit.
Pit Section
Time elapsed
W h e n the LDC g o e s t o L level, the o u t p u t of T A 7 5 4 5 8 ( 1 / 2 )
c h a n g e s t o n e g a t i v e , a n d this a l l o w s bias c u r r e n t of Q 1 0 9 to
a n d A
4
f l o w f r o m its e m i t t e r t o the base, t h u s Q 1 0 9 is t u r n e d o n a n d
the Laser d i o d e e m i t s infrared light ( 8 1 0 m m ) .
W h e n light e m i t t e d f r o m the laser d i o d e is i m p i n g e d t o the pin
d i o d e , a c u r r e n t p r o p o r t i o n a l t o s t r e n g t h of the light f l o w s
f r o m a n o d e to c a t h o d e of the d i o d e . W i t h the strength of the
light i n c r e a s e d , a v o l t a g e d e v e l o p e d across R 1 1 3 also i n ­
creases a n d m a k e s n o n - i n v e r t e d ( + ) t e r m i n a l of the o p e r a ­
tional
amplifier
t u r n s
amplifier o u t p u t also increases in positive, t h u s r e d u c i n g the
c u r r e n t f l o w i n g into the laser d i o d e .
e a c h
electrical
signal
c o n v e r t e d
, A
, A
x
2
+ A A r e e v a l u a t e d . N a m e l y , b o t h phases f o r
+ A
are the
s a m e w h e n
4
Inside of
the track
On a track
Outside of
the track
On a track
Inside or outside
of the track
Sum signal
Inside of
the track
Difference
Signal
Outside or
the track
positive.
A s
t h e
result,
t h e
by
the
A n d A
, a n d
3
4
the t r a c k i n g
is
operational

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