CD CORE UNIT
VDD(+ 3.3 V)
1.1 PREAMPLIFIER BLOCK (PE5497B: IC201)
In the preamplifier block, the pickup output signals are processed to generate signals that are used in the subsequent
blocks: servo, demodulator, and control blocks. Signals from the pickup are I/V converted in the pickup with the
preamplifier with built-in photo detectors, and after added with the RF amplifier, they are used to produce such signals as
RF, FE, TE, and TE zero-cross signals. The preamplifier block is built in CD LSI PE5497B (IC201), whose parts are
described individually below. Incidentally, as this LSI employs a single power supply (+ 3.3 V) specification, the reference
voltages of this LSI and the pickup are the REFO (1.65 V) for both. The REFO is an output obtained from REFOUT in the
LSI via the buffer amplifier, and is output from the pin 93 of this LSI. All measurements will be performed with this REFO
as the reference.
Caution: Be careful not to short-circuit the REFO and GND when measuring.
1.1.1 APC (Automatic Power Control) circuit
Since laser diodes have extremely negative temperature characteristics in optical output when driven in constant current,
it is necessary to control the current with the monitor diodes in order to keep the output constant. This is the feature of the
APC circuit. The LD current is obtained by measuring the voltage between LD1 and VDD(+ 3.3 V), and divide the value by
7.5 (ohms), which becomes about 30 mA.