TDA1301 Philips Semiconductors, TDA1301 Datasheet - Page 4

• Manufacturer Part Number: TDA1301
• Description: Digital servo processor DSIC2
• Manufacturer: Philips Semiconductors

Philips Semiconductors
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 V
V
is given in equation (1).
March 1994
RH
Digital servo processor (DSIC2)
. The maximum current for the central diodes signals
Fig.3 Diode configuration.
RL
and
5
The maximum current for the satellite signals is given in
equation (2).
V
(1.0, 1.5, 2.0 and 2.5 V) which can be selected under
software control. In the application V
V
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:
Where the detector set-up is assumed to be as illustrated
in Fig.3.
I
I
FE
i max
i max
RH
SSA
n
is generated internally. There are four different levels
. It is also possible to drive V
=
=
=
--------------------- -
D1
D1 D2
f
f
sys
sys
–
+
D2
V
V
–
RH
RH
--------------------- -
D3
D3 D4
–
–
–
+
V
V
D4
RL
RL
1.5 10
0.75 10
RH
RL
with an external
Product specification
TDA1301T
–
is connected to
6
–
6
A
A
(1)
(2)
(3)