SM4712 Nippon_Precision_Circuits America, SM4712 Datasheet - Page 12

• Manufacturer Part Number: SM4712
• Description: DVD RAM Head Amp ic
• Manufacturer: Nippon_Precision_Circuits America

Tracking Signal Processor
The tracking stage generates the push-pull tracking
error signal and output signal for DPD servo, as well
as a push-pull sum signal used as an auxiliary signal.
The [(A + B)
mon-data front-end amplifier and signal processor
block is sent to the gain switching block. The gain
switching block amplifies the difference signal using
one of 16 preset gain settings in 2 dB steps to form a
push-pull signal output on TSUB. A feedback resis-
tor connected to TSUBB is used to ensure gain set-
ting stability. The gain of the gain switching block is
controlled by serial interface control bits as shown in
table 2.
Each signal from T1, T2, T3, T4 is buffered and then
output on DPDA, DPDB, DPDC, DPDD, respec-
tively, for DPD servos.
The auxiliary signal is generated from the push-pull
sum signal (A + B + C + D). This signal is buffered
(TAB) and output on TADD. A feedback resistor
connected to TADDB is used to ensure gain setting
stability.
Focus Signal Processor
The focus stage generates the focus error signal from
the focus PD, and a sum signal. The weak focus PD
current signals (F1, F2) are input to the front-end
amplifier and then current-to-voltage converted at
fixed gain.
The front-end amplifier output is sent to the signal
processor block where the focus error signal (F1
F2) and the sum signal (F1 + F2) are generated.
The focus error signal is sent to the gain switching
block. The gain switching block amplifies the differ-
ence signal using one of 16 preset gain settings in 2
dB steps with output on FSUB. A feedback resistor
connected to FSUBB is used to ensure gain setting
stability. The gain of the gain switching block is con-
trolled by serial interface control bits as shown in
table 3.
The sum is buffered and output on FADD. A feed-
back resistor connected to FADDB is used to ensure
gain setting stability.
(C + D)] signal from the com-
SM9103M
Table 2. TSUB gain setting
1. Default is 0 dB
Table 3. FSUB gain setting
1. Default is 0 dB
TG3
FG3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
TG2
FG2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
NIPPON PRECISION CIRCUITS—12
TG1
FG1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
TG0
FG0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Gain (dB)
Gain (dB)
+14
+12
+10
+14
+12
+10
+8
+6
+4
+2
+8
+6
+4
+2
0
10
12
14
16
0
10
12
14
16
2
4
6
8
2
4
6
8
1
1