Kenwood DP-1100 B, Руководство по обслуживанию

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DP-1100B II
II.
FUNDAMENTALS
5 - 2 - 2 T r a c k i n g Error D e t e c t i o n
T r a c k i n g e r r o r is a d e v i a t i o n of t h e r e a d i n g light s p o t f r o m t h e
pits (track) t o be t r a c e d .
In t h e P i c k u p a m e t h o d c a l l e d " h e t e r o d y n e s y s t e m " is
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 b a s e d u p o n t h e d i s t r i b u t i o n of t h e
r e f l e c t e d l i g h t 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 o f t h e pit a n d s p o t .
In this s y s t e m , e a c h electrical signal c o n v e r t e d by t h e
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
x
, A
2
, A
3
A n d A
4
, a n d
A
t
+ A
3
a n d A
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
t
+ A
3
a n d A
2
+ A
4
are t h e s a m e w h e n t h e t r a c k i n g is
e s t a b l i s h e d , w h i l e phase d i f f e r e n c e w i l l be c a u s e d w h e n t h e
s p o t deviates f r o m a pit.
F i g . 5 . 5 P I C K U P Radial Signal S a m p l i n g T h e o r y (Pit depth X/4)
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
x
, A
2
, A
3
a n d A
4
d e v e l o p e d b y t h e 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 p r o v i d e EFM s i g n a l . 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 t h e LDC g o e s H, t h e o u t p u t of T A 7 5 4 5 8 ( Q 1 0 8 )
b e c o m e s positive as s h o w n in t h e 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 R 1 4 5 , D 1 0 2 , A n d D 1 0 4 t u r n s
Q 1 0 9 c u t off, t h e r e b y s t o p s t h e oscillation of t h e Laser D i o d e .
W h e n t h e LDC g o e s t o L level, t h e 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
f l o w f r o m its e m i t t e r t o the b a s e , 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 t h e laser d i o d e is i m p i n g e d t o t h e 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 t h e 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 t h e s t r e n g t h of t h e
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 a c r o s s 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 t h e o p e r a ­
tional a m p l i f i e r positive. A s t h e result, t h e o p e r a t i o n a l
a m p l i f i e r o u t p u t also increases in p o s i t i v e , t h u s r e d u c i n g t h e
c u r r e n t f l o w i n g into t h e laser d i o d e .
3 0
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
Pit Section Time elapsed