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3. FOCUS ERROR AMPLIFIER
The focus error amp is the difference between RF I – V AMP (1) output V
A
and RF I – V AMP (2) output
V
B
. This two (V
A
, V
B
) signals are each applied to the (-) and (+) input of focus error amp. As the result of
differential voltage, Focus error signal is appeared at FE1 Pin (Pin57). This FE1 Output Voltage (low
frequency) becomes (A + C) – (B + D), as follow V
FE1
= R1/R3 (V
B
– V
A
)
The focus error voltage is directed to the focus servo Block, to maintain optimum focusing at all times.
4. FOCUS OK GENERATION CIRCUIT
The focus OK circuit generates a timing window to monitor focus search status of focus servo. When
RFO (Pin 66) Voltage is more than –0.37V, the focus OK circuit is inverted. Time constant of HPF in EFM
comparator and in mirror circuit and that of LPF in focus OK circuit are determined bu capacitor (0.01
µ
F)
between RFI and RFO.
FL8550
16
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