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CIRCUIT DESCRIPTION
Tracking error amplifier
The current from the side spot photodiodes is input to pins E
and F and is converted to a voltage by the E I-V amplifier and F
|-V amplifier respectively.
That is:
Vr =iF Xx 403 k-ohms
Ve=IEx 260 k-ohms x Ra/(Ra+ 22 k)+(Ra+ 260 k)
Focus OK circuit
The focus OK circuit creates a timing window,
turning the
focusing servo ON with the focus search status.
While an RF signal is present at pin @)an HPF output is pre-
sent at pin). At the same
time, the LPF output (opposite
phase) of the focus OK amplifier is obtained.
The focus OK output is inverted when
Vari— Varo is almost
equal to —0.37 V.
26K
TRACKING
ERROR
AMP
The difference
between
the E I-V amplifier and the F I-V
amplifier is calculated by the tracking error amplifier, and the
photodiode (E-F) current is converted to a voltage and output.
Vtte=(Ve—VeF) x 3.2
=(iE-iF) x 1290 k-ohms
Focus
OK
COMPARATOR
C34 is used to determine the time constants of the EFM com-
parator, the HPF in the mirror circuit, and the LPF in the focus
OK
amplifier.
Normally,
C34=0.01
pF is selected,
with
fc=1
kHz. This will prevent degradation of the block error
rate due to an RF envelope lack caused by cracks, etc. on the
disc.
19
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