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4) Focus Error Amplifier
The photo-detector outputs (A + C) and (B + D) are passed
through a differential amplifier and an error amplifier, and
then (A + C − B − D) is output from Pin 91 as the FE signal.
The FE voltage low frequency component is :
FE = (A + C − B − D) ×
= (A + C − B − D) × 5
Using REFO as the reference, an S-curve of approximately 1.5
Vpp is obtained for the FE output. The final-stage amplifier
cutoff frequency is 11.4 kHz.
CN101
A+C
6
B+D
13
5) Tracking Error Amplifier
The photo-detector outputs E and F are passed through
a differential amplifier and an error amplifier, and then
(E − F) is output from Pin 93 as the TE signal. The TE
voltage low frequency component is :
224k
TE = (E − F) ×
112k
= (E − F) × 6.6 (Effective LSI output is 5.0).
Using REFO as the reference, the TE waveform of
approximately 1.3 Vpp is obtained for the TE output.
The final-stage amplifier cutoff frequency is 20 kHz.
CN101
F
9
E
11
Fig.5 TRACKING ERROR AMPLIFIER AND TRACKING ZERO CROSSING AMPLIFIER
16k
80k
×
(20k + 5k)
10k
FE OFFSET
10k
82
48k
83
16k
84
48k
85
16k
10k
Fig.4 : FOCUS ERROR AMPLIFIER
160k
×
48.7k
F
86
112k
224k
E
87
48k
112k
224k
C219 180pF
FE
90
91
D/A
80k
110k
5k
20k
5k
20k
6) Tracking Zero Crossing Amplifier
TEC signal (the tracking zero crossing signal) is
obtained by multiplying the TE signal four times. It is
used for locating the zero crossing points of the track-
ing error. The zero cross point detection is done for the
following two reasons :
1 To count tracks for carriage moves and track jumps.
2 To detect the direction in which the lens is moving
when the tracking is closed (it is used on the track-
ing brake circuit to be described later).
The TEC signal frequency range is 300 Hz to 20 kHz.
TEC voltage = TE level × 4
Theoretical TEC level is 5.2V. The signal exceeds D-
range of the operational amplifier and thus is clipped.
It, however, can be ignored since this signal is used by
the servo LSI only at the zero crossing point.
C220 51pF
92
93
D/A
80k
80k
110k
110k
TE OFFSET
48.7k
48k
20k
48.7k
YPM-2306ZF
A/D
TO DIG. EQ
TE
A/D
TO DIG. EQ
TE2
94
C221
60k
95
6800pF
TEC
31