Fig.4-17
The DC-replayed Envelope signal J is obtained from
the differentia! amplitude of these Peak and Bottom
Hold signals, H and I. The Mirror output is
obtained by comparing this signal J with the signal
K which has been held at peak level, using a time
constant of a a level that is two-thirds that of the
peak value. In other words, the Mirror output is
"L"
upon a disc track or "H" between disc tracks
(the Mirror section). Moreover, the Mirror output is
also "W when a defect has been detected.
EFM COMPARATOR
Fig.
4-18
The EFM Comparator functions to convert the RF the reference voltage of the EFM comparator is
signals into binary signals. The asymmetry caused controlled by exploiting the respective 50% proba-
by variance during disc manufacture cannot be bility of a 1 or 0 occurring as the value of a
eliminated merely by AC coupling. Consequently, binary-coded EFM signal.
25
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