SAA7824 Datasheet, PDF (30/89 Pages) NXP Semiconductors – CD audio decoder, digital servo and filterless DAC with integrated pre-amp and laser control (PhonIC)

Philips Semiconductors
CD audio decoder, digital servo and filterless
DAC with integrated pre-amp and laser control
Product specification
SAA7824
SHADEN BITS
01
(bank 1)
SHADOW
REGISTER
C
signal magnitude
control for diodes
R1 and R2 (LF
only)
ADDRESS
1100
DATA
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
VOLTAGE (mV)
20
25
30
40
60
75
100
120
150
200
270
350
450
600
720
960
INITIAL
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
reset
7.16.2 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 to be as shown in
Fig.21.
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 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 dropout 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 SAA7824 during initialization.
2003 Oct 01
30