Pioneer YPM-2306ZF 서비스 매뉴얼 - 페이지 33

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10) EFM Circuit

This circuit is used for converting the RF signal to digi-

tal signal consisting of "0" and "1". The RFO signal

from Pin 75 is externally AC coupled, entered to Pin 74,

then applied to the EFM circuit.

Loss of the RF signal due to scratches or stains on the

disc, or vertical asymmetry of the RF due to variations

in the discs manufactured can't be eliminated by AC

coupling alone. This circuit, therefore, controls the ref-

erence voltage ASY on the EFM comparator by use of

the fact that "0" and "1" appear fifty fifty in the EFM

signal. By this arrangement, the comparate level is con-

stantly maintained at almost center of the RFO signal

level. The reference voltage ASY is generated when the

EFM comparator output is passed through the low pass

filter. The EFM signal is output from Pin 71. It is a 2.5

Vp-p amplitude signal centering on REFO.

C213

3900pF

40k

RFI

40k

75k

Fig.9 : EFM CIRCUIT

EFM. SIG

EFM

ASY

40k

15k

YPM-2306ZF

R202

10k

C210

3300pF

R203

39k

C211

0.1µF