CXA1782CQ/CR
1-1. FS4
This switch is provided between the focus error input (Pin 2) and the focus phase compensation, and is in
charge of turning the focus servo ON and OFF.
$00
→ $08
Focus OFF ← Focus ON
1-2. Procedure of focus activation
For description, suppose that the polarity is as described below.
a) The lens is searching the disc from far to near;
b) The output voltage (Pin 6) is changing from negative to positive; and
c) The focus S-curve is varying as shown below.
A
t
Fig. 3. S-curve
The focus servo is activated at the operating point indicated by A in Fig. 3. Ordinarily, focus searching and the
turning the focus servo switch ON are performed during the focus S-curve transits the point A indicated in Fig. 3.
To prevent misoperation, this signal is ANDed with the focus OK signal.
In this IC, FZC (Focus Zero Cross) signal is output from the SENS pin (Pin 24) as the point A transit signal. In
addition, focus OK is output as a signal indicating that the signal is in focus (can be in focus in this case).
Following the line of the above description, focusing can be well obtained by observing the following timing
chart.
(20ms) (200ms)
$02
($00)
$03
$08
Drive voltage
Focus error
The broken lines in the figure
indicate the voltage assuming
the signal is not in focus.
SENS pin
(FZC)
The instant the signal is brought into focus.
Focus OK
Fig. 4. Focus ON timing chart
– 23 –
ETC [ ETC ]
