SAA7348GP Datasheet, PDF (14/60 Pages) NXP Semiconductors – All Compact Disc Engine ACE

Philips Semiconductors
All Compact Disc Engine (ACE)
Preliminary specification
SAA7348GP
7.3 Servo functions
7.3.1 SIGNAL CONDITIONING
The digital codes retrieved from the ADCs are applied to
logic circuitry to obtain various control signals. The signals
from the central aperture diodes are processed to obtain a
normalised focus error signal:
FE_n = _{D-D----1-1----+–}-----DD-----22-- – _{D-D----3-3----+–}-----DD-----44--
where the detector set-up illustrated in Fig.5 is assumed.
For single Foucault focusing, signal conditioning can be
switched under software control such that:
FE_n = 2 × _{D-D----1-1----+–}-----DD-----22--
The error signal, FE_n, is further processed by a
Proportional Integral and Differential (PID) filter section.
A Focus OK (FOK) flag is generated by means of the
central aperture signal and an adjustable reference level.
This signal is used to provide extra protection for
Track-Loss (TL) generation, drop out detection and the
focus start-up procedure.
The radial or tracking error signal is generated by the
satellite detector signals R1 and R2. The radial error signal
can be formulated as follows:
RE_s = (R1 − R2) × re_gain + (R1 − R2) × re_offset
where the index ‘s’ indicates the automatic scaling
operation performed on the radial error signal. This scaling
is necessary to avoid non-optimal dynamic range usage in
the digital representation and to reduce the radial
bandwidth spread. Furthermore, the radial error signal will
be free of offset during disc start-up.
The four signals from the central aperture detectors,
together with the satellite detector signals, generate a
track position signal (TPI), which can be formulated as
follows:
TPI = sign [(D1 + D2 + D3 + D4) − (R1 + R2) × sum_gain]
where the weighting factor sum_gain is generated
internally by the SAA7348 during initialization.
handbook, full pagewidth
SATELLITE
DIODE R1
D1
D3
D2
SATELLITE
DIODE R2
single Foucault
SATELLITE
DIODE R1
D2 D1
D4 D3
SATELLITE
DIODE R2
astigmatic focus
1997 Jul 11
Fig.5 Detector arrangement.
14
SATELLITE
DIODE R1
D1
D2
D3
D4
SATELLITE
DIODE R2
double Foucault
MBG422