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Writable optical discs record data as low
reflectivity mark sections and high
reflectivity space sections. It is, however,
actually impossible to write data with a
difference in laser power of only a factor
of two. Therefore it is necessary to provide
multiple levels of laser power and to
control the timing of the edges where the
power level changes with high precision
to support a wide variety of media. This
timing control function is called the write
strategy (WS). (See figure 8.)
In the structure of a typical writable optical
disc drive, the write strategy timing
and the APC power monitoring signals are
transmitted over a flexible flat cable
(FFC). In 8×-speed Blu-ray Disc recording,
the signal degradation due to this
transmission would have a large negative
impact on recording quality. (See figure
9.)
For the LDD developed in this effort Sony
proposed a structure that does not require
transmission of high-speed signals over a
flexible flat cable by not only integrating
the write strategy function, but also by
supplying the sampling pulse signal from
the previously mentioned power monitor
PDIC that includes an integrated sample-and-
hold circuit.
Sony suppressed the power consumption
increase due to the write strategy integration
that includes implementing complex
write strategy patterns to a practical level
by major revisions of the circuit architecture.
Since the APC power control system
also follows the current interface
method, it will be easy to achieve the transition
to this Sony proposed system. (See
figure 10.)
While the 8×-speed Blu-ray Disc recording
channel clock will be 530 MHz, these
devices achieve both an adequately low
jitter and a uniform 59 ps resolution as
the basic performance required to assure
recording quality. (See figure 11.) |
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LDD
Vol.50