HA12220F Datasheet, PDF (13/20 Pages) Hitachi Semiconductor – CD-ROM Drive Head Amplifier IC

HA12220F
Mirror Detection Circuit (MIRR)
As the pick-up travels across tracks, the EFM RF signal varies as in figure 11 (a). The mirror detection
circuit detects the mirror region from this signal.
The external capacitor on pin 19 integrates the track-crossing frequency component.
The internal time constant of the mirror detection circuit can be set for normal, 4×, or 8× speed by 2-bit
data from the HD49250, to raise the trackable range of track-crossing frequencies. The defect circuit
internal time constant is also switched at the same time.
(a) Pin 22
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(b) Pin 18
Figure 11 Mirror Detection Waveform
Tracking Error Amplifiers
The sub-beam output of PDIC is passed through a resistor and input at pins 4 and 5. External resistances of
pins 4 and 5 should be set according to the pick-up so that the traverse signal at pin 8 is about 2Vpp Typ.
After a reset, the initial value of the feedback resistance BAL of TR1 amplifier is 400kΩ, the same as the
feedback resistance of TR2 amplifier.
BAL has a variable resistance value that is changed by 4-bit data from the HD49250. The variability range
here is from –16 to +14% in 2% steps. This resistance can be varied to adjust the EF balance of the
tracking error.
TE amplifier generates the tracking error signal.
TVR is a resistor that changes the tracking gain from –8 to +8dB in 4dB steps. This is set by 3-bit data
from the HD49250. TVR2 is a variable resistor used to increase the gain by 12dB in CD-RW mode. This
variable resistor is set by 1-bit data from the HD49250.
TLPF switches the tracking error cut-off frequency. The TE output cut-off frequency is set to either 30, 60,
100, or 200kHz (Typ) by 2-bit data from the HD49250.
TR1
4
+ ^TR1
–
BAL
TVR
+TE
–
TLPF +
–
+TA
–
TVR2
TR2
5
1.2p
+ ^TR2
–
TVR
400k
1.2p
Gain=8dB Typ
8
TE
Figure 12 Tracking Error Amplifiers
Rev.1, Apr. 1997, page 13 of 20