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TDA1301T View Datasheet(PDF) - Philips Electronics

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Description
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TDA1301T
Philips
Philips Electronics Philips
TDA1301T Datasheet PDF : 14 Pages
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Philips Semiconductors
Digital servo processor (DSIC2)
Product specification
TDA1301T
FUNCTIONAL DESCRIPTION
Three spots front-end
The photo detector in a two-stage three-spots compact
disc system normally contains six discrete elements. Four
of these elements (in the event of single Foucault: three
elements) carry the central aperture (CA) signal while the
other two elements (satellite signals) carry the radial
tracking information. Besides the HF signal, which is finally
applied to both of the audio channels, the central aperture
also contains information for the focus servo loop. To
enable the HF signal to be processed, the frequency
contents of the central aperture signal must be divided into
an HF data part and an LF servo part. The HF signal is
processed outside the DSIC2 by the TDA1302 or a
discrete amplifier-equalizer. The necessary crossover
point, to extract the LF servo part, is compensated for in
the amplifier.
Diode signal processing
The analog signals from the photo detectors are converted
into a digital representation using analog-to-digital
converters. The ADCs are designed to convert unipolar
currents into a digital code. The dynamic range of the input
currents is adjustable within a given range and is
dependent on the ADC input reference voltages VRL and
VRH. The maximum current for the central diodes signals
is given in equation (1).
Ii (max) = fsys × ( VRH VRL) × 1.5 × 106 [ µA]
(1)
The maximum current for the satellite signals is given in
equation (2).
Ii (max) = fsys × ( VRH VRL) × 0.75 × 106 [ µA]
(2)
VRH is generated internally. There are four different levels
(1.0, 1.5, 2.0 and 2.5 V) which can be selected under
software control. In the application VRL is connected to
VSSA. It is also possible to drive VRH with an external
voltage source but in this situation the internal voltage
source has to be switched off (software controlled).
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 detectors are processed
so that the normalized focus error signal (FE) given in
equation (3) is realized:
FEn = D-D----11-----+–-----DD-----22-- D-D----33-----+–-----DD-----44--
(3)
Where the detector set-up is assumed to be as illustrated
in Fig.3.
March 1994
Fig.3 Diode configuration.
5
 

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