HA12220 Hitachi Semiconductor, HA12220 Datasheet - Page 11

• Manufacturer Part Number: HA12220
• Description: CD-ROM Drive Head Amplifier IC
• Manufacturer: Hitachi Semiconductor

FOK Detection Circuit
This detector is a comparator that generates the FOK signal. FOK is one of the signals that activate the
focus servo.
The FSA amplifier (fc = 53kHz Typ) summes the output from the PDIC. When this output signal becomes
lower than the reference voltage by Vth, pin 17 goes high. This Vth can be set by 2-bit data from the
HD49250.
Vth is set to 0.8V (0dB) after a reset.
Using -com ADC & DAC the voltage of pin 11 had better be set the same voltage as the voltage of pin 10
before focus searching in order to reduce the effect of DC offset voltage at FSA amplifier output.
APC
This circuit is for the Psub laser diode. This circuit is turned on or off by 1-bit data from the HD49250.
28
1
2
3
RF1
RF2
RF3
RF4
120k
120k
120k
120k
Figure 6 FOK Detection
600k
–
+
5p
FSA
Figure 7 APC
6
MD
APC
+
–
FOK
7
BUF
LD
1k
–
+
FOK
CO
CI
11
17
10
Rev.1, Apr. 1997, page 11 of 20
-COM DAC
-COM ADC
HA12220F