saa7372 NXP Semiconductors, saa7372 Datasheet - Page 24

• Manufacturer Part Number: saa7372
• Description: Digital Servo Processor And Compact Disc Decoder Cd7
• Manufacturer: NXP Semiconductors

Philips Semiconductors
7.14
7.14.1
The photo detector in conventional two-stage three-beam
compact disc systems normally contains six discrete
diodes. Four of these diodes (three for single foucault
systems) carry the central aperture signal (CA) while the
other two diodes (satellite diodes) carry the radial tracking
information. The CA signal is processed into an HF signal
(for the decoder function) and LF signal (information for the
focus servo loop) before it is supplied to the SAA7372.
The analog signals from the central and satellite diodes
are converted into a digital representation using
analog-to-digital converters (ADCs). 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, which is dependent on the value of
external resistor connected to pin I
current for the central diodes and satellite diodes is given
in the following formulae;
The V
which ensures that the V
on the spread of internal capacitors, using the reference
1998 Feb 26
I
I
in max central
in max satellite
Digital servo processor and Compact Disc
decoder (CD7)
RH
Servo part
voltage is internally generated by control circuitry
D
IODE SIGNAL PROCESSING
=
=
2.4 10
----------------------- -
1.2 10
----------------------- -
R
R
IrefT
IrefT
RH
voltage is adjusted depending
6
6
G
A
A
refT
. The maximum
Fig.18 Motor servo mode diagram.
4 f
3 f
24
current generated by the external resistor on I
application V
currents for a range of resistors is given Table 10.
Table 10 Maximum current input
This mode of V
by the preset latch command.
Alternatively, the dynamic range of the input currents can
be made dependent on the ADC reference voltages V
and V
satellite diodes is given in the following formulae;
R
IrefT
220
240
270
300
330
360
390
430
470
510
560
620
RH
BW
(k )
. The maximum current for the central diodes and
RL
RH
is connected to V
D1 TO D4 ( A)
MGA362 - 2
DIODE INPUT CURRENT RANGE
automatic adjustment can be selected
10.909
10.000
8.889
8.000
7.273
6.667
6.154
5.581
5.106
4.706
4.286
3.871
f
SSA1
. The maximum input
Product specification
R1 AND R2 ( A)
SAA7372
5.455
5.000
4.444
4.000
3.636
3.333
3.077
2.791
2.553
2.353
2.143
1.935
refT
. In the
RL