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1.1.6 Tracking zero-cross amplifier
The tracking zero-cross signal (hereinafter referred to as TEC signal) is obtained by amplifying the TE signal by fourfold,
and used to detect the tracking-error zero-cross point. As the purpose of detecting the zero-cross point, the following two
points can be named:
1. To use for track-counting in the carriage move and track jump modes
2. To use for detecting the direction in which the lens moves in tracking close. (Used in the tracking brake circuit to be
explained later.)
The frequency range of the TEC signal is from 300 Hz to 20 kHz, and
TEC voltage = TE level x 4
The TEC level can be calculated at 4.62 V, which, at this level, exceeds the D range of the operational amplifier, and clips
the signal, but, because the CD LSI only uses the signal at the zero-cross point, it poses no particular problem.
1.1.7 EFM circuit
The EFM circuit converts the RF signal into digital signals of 0 and 1. The AGCO signal output from the pin 119 is
A/C-coupled externally, input to the pin 118, and supplied to the EFM circuit.
Missing RF signal due to scratches and stains on the disc, and asymmetry of the upper and lower parts of the RF, caused
by variation in disc production, cannot be entirely eliminated in AC coupling process, the reference voltage ASY of the
EFM comparator is controlled, using the probability that 0 and 1 occur at 50%. Thus, the comparator level will always stay
around the center of the RFO signal. This reference voltage ASY is generated by passing the EFM comparator output
through the low-pass filter. The EFM signal is output from the pin 113.
PE5547A
RFI
118
Vdd
40k
40k
Fig.1.1.4 EFM
5
6
Vdd
+
-
+
-
7.5k
1.5k
6
7
+
-
CX-3195
7
8
ASY
114
EFM signal
EFM
113
2k
8
A
B
C
D
E
F
7
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