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CX-3158

1.1 PREAMPLIFIER BLOCK (UPD63763GJ: IC201)

In the preamplifier block, the pickup output signals are processed to generate signals that are used for the next-stage

blocks: the servo block, demodulator, and control.

After I/V-converted by the preamplifier with built-in photo detectors (inside the pickup), the signals are applied to the

preamplifier block in the CD LSI UPD63763GJ (IC201). After added by the RF amplifier in this block, these signals are

used to produce necessary signals such as RF, FE, TE, and TE zero-cross signals.

The CD LSI employs a single power supply system of + 3.3V. Therefore, the REFO (1.65V) is used as the reference volt-

age both for this CD LSI and the pickup. The LSI produces the REFO signal by using the REFOUT via the buffer amplifi-

er and outputs from the pin 133. All the measurements should be made based on this REFO.

Caution: Be careful not to short the REFO and GRD when measuring.

1.1.1 APC (Automatic Power Control)

A laser diode has extremely negative temperature characteristics in optical output at constant-current drive. To keep

the output constant, the LD current is controlled by monitor diodes. This is called the APC circuit. The LD current is

calculated at about 30mA, which is the voltage between LD1 and V3R3D divided by 7.5 (ohms).

Fig. 1.1.1 APC

PICKUP UNIT CD CORE UNIT

LD-

LD+

100/16

2SB1132

2R4 x 2

2R7

VREF

REG 1.25V

APN

LDS

UPD63763GJ

143

142

6R5K

110K

100K

1 2 3 4 5 6 7 8 ... 23 24

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