Sony DVP-M35 Operation Manual page 31

The IC506 Servo DSP: CXD8730 on MB-78 board provides the following control in
the focus servo system.
(a) Focus search
The optical pickup lens is moved toward a disc to turn on the focus servo.
The focus servo loop is turned on when the PI (Pull IN) signal (used for FOK:
Focus OK) exceeds the specification (Vc +0.25V) and the FlE signal zero-crossing
is detected.
(b) Focus gain adjustment
The gain of digital filter in the IC506 is automatically adjusted so that the focus
servo loop gain becomes optimum.
Consequently, the optimum gain for each disc to be played can be attained, besides
correction of gain variations in focus actuator (coil) and optical pickup sensor
(photodiode for focusing).
(c) Focus bias adjustment
The focus bias is added to the focus servo filter so as to minimize the jitter.
Consequently, a variation of optical pickup and disc can be automatically corrected.
(d) Focus jump
Operation carried out when playing back the DVD dual layer disc to perform
focusing jump between layer 0 (PU side layer) and layer 1 (far end layer).
First the servo loop is turned off, the kick voltage is supplied to the focus actuator,
and the focus is jumped to the targeted layer. As the focus approaches the desired
layer, the FE signal appears. The voltage of this signal is monitored, the deceleration
pulse is generated, and the focus servo is turned ON again after focusing.
These operations from the start to end of jumping are all performed inside the
DSP.