Table of Contents
Advertisement
,.
,.
-_-_:.:..
:.:_--.
....
, ,
I
11
\I
,
:
\
~
11
1 1
II
t
1
\I
11
I
I
I
...
___
-----
-
--
REV
SLOW REV
Fig. 2-18. Laser beam trace in each modes of operation
•
STILL Play
'
'
"
II
II
'/
I
The STILL play is the fundamental operation of the trick play.
One track is read and then the beam jumps one track back and
.repeats. As each revolution of the disc is recorded frame (two
fields), the STILL play takes place in the unit of one frame.
•
SLOW FWD Play
The 1/2 SLOW FWD picture is obtained by repeating the STILL
play and the NORMAL play at a constant rate.
•
FAST FWD Play
The FAST FWD Play is made possible by jumping one track
forward after each field and the jumping «;lirection in this case is
opposite to that in the STILL or the SLOW FWD.
•
REV Play
The REV. Play is made possible by jumping two tracks in the re-
verse direction after each revolution of disc.
•
SLOW REV Play
The SLOW REV Play is basically the same as that of SLOW FWD
Play that is made possible by repeating the STILL Play and the REV
Play at a constant rate.
18
•
How the track jump takes place will be describ,ecfbriefly. There
are two kinds of the jumps. All the track jumps are the REV jumps
except the FWD jump in the FAST FWD mode. Fig. 2-19 shows the
timings of the FWD jump and the REV jump.
The tracking servo loop switch is opened at the V-sync timing
upon receiving a REV jump command. Then the mirror is driven in
the REV direction.
As the mirror is moved, the tracking detection beam is shifted out
from the track by 1/2 track amount, that produces the half of the
tracking error voltage similar to a sine curve. The error voltage of
"zero" is provided for a moment. The "zero" voltage is the zero-
cross signal which is produced when the laser beam is located in the
middle of two adjacent tracks. A deceleration signal in the FWD
direction is impressed on the mirror drive signal at the zero cross
moment. When the beam is positioned correctly· on the adjacent
track, the error voltage becomes zero again and then the tracking
servo loop is closed by the zero detection signal. The normal track-
ing servo operation is restored.
' The FWD jump is the same sequence as that of the REV jump
except that the drive direction of the mirror is opposite. ,
V-SYNC
TRACKING
LOOPSWITCH
REV
ACCELERATE
FWD
ACCELERATE
MIRROR
DRIVE
TRACKING
ERROR
PREVlOUSI
TRACK
REV JUMP
~REVJUMP
®
©
(j)
FWD
JUMP
SERVO LOOP OPEN
®
~
} "
0
®
:\)
- F W D
J U M P - - - -
Fig. 2-19. Track jump system
~/
I
AOJACENT
TRACK
Advertisement
Table of Contents
