HA12220 Hitachi Semiconductor, HA12220 Datasheet - Page 10

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

HA12220F
RF Amplifiers
The output from PDIC is summed by RFS amplifier.
Figure 4 shows the equivalent circuit for the EQ block in figure 3. The peaking characteristics can be
changed with 4-bit data from the HD49250.
On resistance of SC1 to SC4 are 600 Typ.
The RFS amplifier output is input to the AGC amplifier internally in the IC.
Pin 24 is used to connect the capacitor that sets cut-off frequency of high-pass filter between the RFS
amplifier and the AGC amplifier. The cut-off frequency will typically be 80Hz with the external constants
shown in figure 5.
The RF signal is rectified by an internal resistor and an external capacitor connected to pin 23.
The pins 28, 1, 2, and 3 expect an input level of about 0.1Vpp. The AGC amplifier output (pin 22) will
have an amplitude of 1.2Vpp Typ.
When CD-RW mode is set by 1-bit data from the HD49250, the AGC amplifier gain is increased by 12dB.
This allows the IC to output a 1.2Vpp Typ amplitude even during CD-RW playback.
Rev.1, Apr. 1997, page 10 of 20
Figure 4 RFS Amplifier Equalizer Equivalent Circuit
from RFS
Gain changing
28
1
2
3
24
RF1
RF2
RF3
RF4
+
SC3
RFC
1
AGC
Figure 5 AGC Amplifier
Figure 3 RFS Amplifier
23
1.58k
SC2
12k
12k
12k
12k
4k
AGCF
0.1
4p
to HD49250
SC1
4k
8p
22
EQ
–
+
RFS
AGCO
0.3p
SC4
16p
to DEFECT MIRR
to AGC