SAA7372 Datasheet, PDF (25/60 Pages) NXP Semiconductors – Digital servo processor and Compact Disc decoder CD7

Philips Semiconductors
Digital servo processor and Compact Disc
decoder (CD7)
Product specification
SAA7372
I_{in (max, central)} = f_sys × ( V_RH – V_RL) × 1.0 × 10^–6 µA
I_{in (max, satellite)} = f_sys × ( V_RH – V_RL) × 0.5 × 10^–6 µA
Where f_sys = 4.2336 MHz.
V_RH is generated internally, and there are 32 levels which
can be selected under software control via the preset latch
command. With this command the V_RH voltage can be set
to 2.5 V then modified, decremented one level or
incremented, by resending the command the required
number of times. In the application V_RL is connected to
V_SSA1.
7.14.2 SIGNAL CONDITIONING
The digital codes retrieved from the ADCs are applied to
logic circuitry to obtain the 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 is assumed as shown in Fig.19.
In the event of single Foucault focusing method, the signal
conditioning can be switched under software control such
that the signal processing is as follows;
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 the
track-loss (TL) generation, the focus start-up procedure
and the drop out detection.
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 which is performed on the radial error signal.
This scaling is necessary to avoid non-optimum dynamic
range usage in the digital representation and reduces the
radial bandwidth spread. Furthermore, the radial error
signal will be made free from offset during start up of the
disc.
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 SAA7372 during initialization.
handbook, full pagewidth
SATELLITE
DIODE R1
D1
D3
D2
SATELLITE
DIODE R2
single Foucault
1998 Feb 26
SATELLITE
DIODE R1
D2 D1
D4 D3
SATELLITE
DIODE R2
astigmatic focus
Fig.19 Detector arrangement.
25
SATELLITE
DIODE R1
D1
D2
D3
D4
SATELLITE
DIODE R2
double Foucault
MBG422