SAA7806H NXP [NXP Semiconductors], SAA7806H Datasheet - Page 49

• Manufacturer Part Number: SAA7806H
• Description: One chip automotive CD audio device
• Manufacturer: NXP [NXP Semiconductors]

Philips Semiconductors
9397 750 13697
Objective data sheet
6.7.4.1 Focus start-up
6.7.4 Focus servo system
An internal 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 dropout detection.
The radial or tracking error signal is generated by the satellite detector signals R1 and R2.
The Radial Error (RE) signal can be formulated as follows:
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 Indicator (TPI) which can be formulated as follows:
where the weighting factor sum_gain is generated internally by the SAA7806 during
initialization.
Five initially loaded coefficients influence the start-up behavior of the focus controller. The
automatically generated triangular voltage can be influenced by 3 parameters; for height
(ramp_height) and DC offset (ramp_offset) of the triangle and its steepness (ramp_incr).
For protection against false focus point detections, two parameters are available which are
an absolute level on the CA signal (CA_start) and a level on the FE
When this CA level is reached then focus has been achieved.
RE
TPI
Fig 29. Detector arrangement
s
=
=
single Foucault
SATELLITE
SATELLITE
DIODE R1
DIODE R2
sign D1
D3
R1 R2
–
D1
D2
+
D2
re_gain
+
Rev. 01 — 20 June 2005
D3
+
+
D4
R1
+
–
R2
R1
astigmatic focus
+
re_offset
SATELLITE
SATELLITE
DIODE R1
DIODE R2
D2
D4
R2
D1
D3
sum_gain
One chip automotive CD audio device
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
n
signal (FE_start).
SAA7806
double Foucault
SATELLITE
SATELLITE
DIODE R1
DIODE R2
D1
D2
D3
D4
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