Chapter 6. Theory of Operation
EK–MOL80–SV. B01
6–19
Read/Write Channel Electronics
Read/write channel electronics take analog data from the optical head and
convert it into digital “transitions”. These transitions are decoded by the
encoder/decoder electronics in the controller chip to extract data from format and
error correction features. The write channel electronics take the serial data
stream from the encoder/decoder and convert the digital pulses into analog data.
This data is then sent to the optical head.
Loading Motor
The loading motor loads and unloads the optical disk cartridge. The loader motor
includes a gear train and a rack and pinion system that allow the cartridge shuttle
to raise and lower the cartridge within the loader housing.
Bias Magnet
The bias magnet subassembly sits on top of the cartridge shuttle and provides the
correct polarity for erasing or writing data.
Optical Head
The optical head assembly contains both mechanical and electronic components
and is a “slip optics” design. This design physically separates the laser diode and
its associated detectors from the focus/fine position actuators, providing
significant seek time performance advantage due to less mass on the moving
portion of the optical head.
The actuators and laser diode (and associated detectors) are on a small PCA on
the optical head assembly. The main components are as follows:
Auto Laser Power Control (ALPC)
Controls the intensity and duration of the laser beam for erase, write, and read
operations.
Focus Servo (Fcs)
Controls the vertical motion of the objective lens to focus the laser beam on the
disk surface.
Fine Tracking Servo (Trk)
Controls the horizontal motion of the objective lens to follow the track of the
disk.
Linear Motor (LM)
Positions the actuator in the vicinity of the desired track on the disk.
