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1
1.1.6 Tracking zero-cross amplifier
A
The tracking zero-cross signal (hereinafter TEC signal) is obtained by amplifying the TE signal 4 times, and used to
detect the tracking-error zero-cross point.
By using the information on this point, the following two operations can be performed:
1. Track counting in the carriage move and track jump modes
2. Sensing the lens-moving direction at the moment of the tracking close (The sensing result is used for the tracking
brake circuit as explained below.)
The frequency range of the TEC signal is between 300Hz and 20kHz.
TEC voltage = TE level x 4
The TEC level can be calculated at 5.2V. This level exceeds the D range of the operational amplifier, and the signal gets
B
clipped. However, it can be ignored because the CD LSI only uses the signal at the zero-cross point.
1.1.7 EFM
The EFM circuit converts the RF signal into a digital signal expressed in binary digits 0 and 1. The AGCO output from
the pin 116 is A/C-coupled in the peripheral circuit, fed back to the LSI from the pin 115, and sent to the EFM circuit
inside the LSI.
On scratched or dirty discs, part of the RF signal recorded may be missing. On other discs, part of the RF signal
recorded may be asymmetric, which was caused by dispersion in production quality. Such lack of information cannot
be completely eliminated by this AC coupling process. Therefore, by utilizing the fifty-fifty occurrence ratio of binary
digits (0 and 1) in the EFM signal, the EFM comparator reference voltage ASY is controlled, so that the comparator
C
level always stays around the center of the RFO signal. The reference voltage ASY is made from the EFM comparator
output via the low-pass filter. The EFM signal is put out from the pin 111.
RFI
115
D
40 k
40 k
E
Fig. 1.1.4 EFM
F
6
1
2
Vdd
Vdd
+
-
1.5 k
7.5 k
2
3
UPD63760GJ
+
-
+
-
CX-3057
3
4
ASY
112
EFM signal
EFM
111
2 k
4
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