Philips CDR880 - Continued Servo Functions; Continued Wobble Processing

BASICS CDR/RW
16
EFMCK
48 mw
Power
(EFM)
0.5mW
t
= measure_of
A = absorbtion
CAc
l
Lens
t
eens anane 6
Hold
(NEN)
eo ~!
Figure 24
Sample and hold
In the Alfa circuit this measured absorption has been
compared with the stored absorption values of the first AlfaO
setpoint. The difference has to be corrected via the Alfa circuit.
3.2.2.3 Normalizing
The normalizing function normalizes the photodiode signals
from the LDU. The reason for normalizing is the great differen-
ce in reflection of various discs. To prevent the influences of
these variations in the rest of the circuits all photodiode
signals are brought to the "normal" level in the beginning of
the circuit. The normalizer processes in this way the sum-
signal of the mainspot called: Central Aperture (CA), but also
the focus and radial error signals. The output signals are
called FEN, REN, CAN. From the CA signal is made a push
pull signal too. That normalized signal is called: PPN. From
the HF-sumsignal the HF signal has been formed. In the read
mode this signal has been directed to the decoder panel after
equalization in the Modulation Transfer Function. In the write
mode this signal has been switched to the Alfa circuit.
3.2.3 The Servo Functions
The electrical circuitries of the turntable motor control and
focus and radial servo drivers are on the main board. These
servo Circuits execute the recorder commands via an own
servo microcontroller (Servo uP) and the main functions are:
- communicating with the master pP (System Controller).
- processing the single commands from the master uP.
- reporting the error conditions to the master uP.
The servo devices on the mainboard also processes the error
signals received from AEGER IC on the CDM Board like:
- controlling the turntable motor in recording and play-back
mode.
- controlling the focus- and radial actuator.
- controlling the slide movement.
3.2.3.1 Turntable Motor Control in recording and play-back
mode
In the read mode the turntable motor has been controlled by the
Pulse Width Modulation (PWM) signal from the CD-Decoder.
In this IC the received HF sumsignal (HFM) from AEGER is
sliced and fed to a phase locked loop circuit after which a FIFO
is filled with the extracted data. Nominally the disc speed
should be such that the FIFO is filled halfway. The amount the
FIFO is filled is compared with the nominal value and the
resulting error signal is the MOTO 1/2 signal used to activate
via the Servo microcontroller the turntable motor control circuit.
In the write mode the ATIP information in the pregroove is
used. This groove carries a modulated frequency of 22.05
kHz. This frequency is present in the PPN signal from
AEGER. To have speed adjusted the received wobble
frequency is compared with the fixed frequency in the wobble
processing unit. Via CDCEP the MPWM signal is sent to the
servo microcontroller, which controls on its turn the turntable
Hallmotor.
3.2.3.2 Focus servo
After normalization in the AEGER the focus error signal (FEN)
will be directed to the Digital Servo IC for Recordable CD
(DSICR) on the Main Board.
The focus servo function starts with the start up, to move the
actuator through the focal point. From the DSICR the digital
message focus found will be sent to the Servo micro
controller. Other digital signals are directed to Digital Servo
Driver IC (DSD) to keep the spot in focus with the disc.
3.2.3.3 Radial servo
After normalization in the AEGER the error signal of radial
servo (REN) will be directed to the DSICR.
The radial servo delivers the following functions:
- radial actuator control.
- slide movement control.
During normal tracking operation the REN signal is processed
in the AEGER into a DC error signal which provides the radial
actuator. Most of the time the slide motor is not driven.
The radial actuator, while keeping track, will slowly move
outward related to the slide and this is resulting in a growing
radial integrator voltage. Each time this voltage exceeds a
certain value, a slide step is generated, resulting in a sudden
outward movement of the slide and hence a radial error drop.
Much more functionality is required during all kinds of non-
linear operations, like starting up, catching track, jumping,
playing across drop-outs, handling shocks and so on. All
these operations require many additional switching functions
which are provided in DSICR. These transfer function
coefficients are programmed in the EEPROM.
3.2.4 The Wobbie Processing
In the recording mode the normalized HF-signal (PPN) is lead
to the wobble processing unit. Here the pregroove information
has been decoded. The carrier frequency of the PPN signal
(22.05 kHz) is compared to a reference frequency. The result
is converted into an errorsignal that controls the turntable
motor and the modulation on that carrier is demodulated to
the time-code information.
Service disc systems PH i Li PS