51
Photo Detectors
The three beams of light are reflected from the disc and returned to the
optical assembly. They land on the photodetectors within these three
groups.
E F
A D
C B
G H
KHM - 220AAA
PHOTO DETECTORS
The voltages from these detectors are matrixed by RF Amplifier IC001
that follows (on the TK-51 board) into servo correction and disc identifica-
tion signals.
Photo Detector Manufactured Signals
Photo
Detectors Signals
Produced Purpose
A – D TE (DVD only)
FE, PI, Mirr., RF
(eye pattern)
TE – DVD tracking error
FE – Focus error
PI – “Pull In” is the analog sum of A-D
detectors used to ID the disc and
create MIRR.
MIRR – mirror signal goes high (4V) if
PI is above a threshold. MIRR is used
to count tracks and ID the disc.
RF – Audio and Video Data
E, F * TE +, TZC CD Tracking error, track count.
G,H * TE –, TZC CD Tracking error, track count
*In CD and older DVD players, there are only two outer tracking error
detectors (E & F). In this new laser assembly, two outer detectors were
added but they are not used in this player.
The extra detectors are to permit this laser assembly to read DVD-R discs
in future players. This DVD player cannot play DVD-Recordable discs
even though the laser has the ability to do so. Detectors E & F are added
together and treated as one. G & H detectors are also added in the matrix
/ RF amp IC001 that follows (not shown).