CXA2542AR
Mirror Circuit
The mirror circuit performs peak and bottom hold after the RFI signal has been inverting amplified.
For the peak hold, a time constant can follow a 30kHz traverse, and, for the bottom hold, one can follow the
rotation cycle envelope fluctuation.
FOK
1V
DEFECT
RF_O
RF
MIRROR HOLD AMP
1.5k
31
30
51k
0.033µ
FOK
C5
0.01µ
29
CP
LPC
22k
J
H
I
PEAK &
BOTTOM
HOLD
× 1
× 1.4
RF_I
G
K
MIRR
MIRROR AMP
SENS
SELECTOR
24
SENS2
MIRROR
COMPARATOR
RF_O
0V
0V
G
(RF_I)
H
(PEAK HOLD)
0V
0V
I
(BOTTOM HOLD)
J
K
(MIRROR HOLD)
H
L
MIRR
The DC restored-envelope signal J is obtained by amplifying the difference between the peak and bottom hold
signals H and I. Signal J has a large time constant of 2/3 its peak value, and the mirror output is obtained by
comparing it to the peak hold signal K. If the value of C5 is made smaller, the low frequency component of the
RF signal is cut off and the amplification of the signal G gets small. Then, that of the signal J gets also small
and the signal K level becomes low, resulting in the short mirror output pulse width. Accordingly, when on the
disc track, the mirror output is Low; when between tracks (mirrored portion), it is High; and when a defect is
detected, it is High. The mirror hold time constant must be sufficiently large compared with the traverse signal.
– 27 –
SONY [ SONY CORPORATION ]
