Devices Mounted in the OP |
| . |
. |
In general, both an LDD that drives the
laser and PDICs, which are photodetector
ICs, are mounted in the OP. There are
two PDICs: an RF/servo signal detection
PDIC that converts the light reflected
from the disc to an electrical signal and a
power monitor PDIC that monitors the
laser power. (See figure 1.) The RF/servo
PDIC has the roles of detecting both control
signals, such as the OP focus signal
and the tracking signal, and the playback
data signal from the light reflected from
the disc. The power monitor PDIC is a
device that functions as the metric for the laser automatic power control (APC) system.
This device directly monitors the
laser output and monitors the laser power
during reading and writing.
Figure 1 Optical Pickup Structure Overview
|
|
|
PDIC - RF/Servo |
| . |
. |
| Extremely fast response and gain settings
that support the recording and playback
levels for a variety of media are required
to achieve practical 8×-speed Blu-ray
Disc recording and playback. Also, as the
speed multiple increases, the PDIC becomes
the main contributing factor to
noise in the playback signal. Therefore
the designers cannot simply aim to increase
the bandwidth, they must also
achieve lower noise. In the RF/servo
PDIC developed in this effort using a new
process, Sony (a) reduced the parasitic
capacitance by using finer fabrication, (b)
used high-precision capacitors, and (c)
took full advantage of new circuit technologies
to achieve a multi-stage (8-stage)
gain switching in the transimpedance amplifier
and at the same time reduce the
noise by a significant -4.4 dB (as compared
to current Sony products). (See figure
2.) Also, to make it possible to achieve
8×-speed Blu-ray Disc recording and
playback, Sony achieved the wide bandwidth
of fc = 230 MHz, which is approximately
twice that of current products. (See
figure 3.) This performance is fully adequate
to handle the fastest signals that
occur in 8×-speed Blu-ray Disc playback
(the 2T iteration × 8 = 132 MHz). |
|
|
PDIC - Power Monitor |
| . |
. |
Improving the response speed of the
power monitor PDIC is required to
achieve 8×-speed Blu-ray Disc recording.
When reading out data during playback,
the laser operates in a DC optical generation
mode, and it is not necessary for the
power monitor to respond quickly. However,
when writing data to a disc, the laser
operates in a pulse optical generation
mode, and rapidly changing signals are
input. The APC system during recording
samples both the mark level when writing
data to the disc and the space level
when not writing data, and this operation
is established by correct monitoring of the
laser output. The longest mark or space
period in 8×-speed Blu-ray Disc recording
is 15.15 ns, and the power monitor
output signal must settle within this period.
The power monitor PDIC developed
using a new process during this effort
achieves both a wide range gain adjustment
function (see figure 4) and the high-speed
settling performance (8 ns, Typ.)
required for 8×-speed Blu-ray Disc recording
while transmitting over a flexible PC board. (See figure 5.) We also reduced
the number of external components in the
OP by moving the external resistor conventionally
required for gain adjustment
into the IC.
Sony has additionally proposed integrating
the sample-and-hold circuit in the
power monitor. (See figure 6.) In the conventional
approach, reduced settling performance
and other signal degradations
occur when transmitting analog signals to
the flexible PC board. Sony, however,
eliminated the influence of the transmission
to the flexible PC board by integrating
the sample-and-hold circuit in the
power monitor developed in this project.
This made it possible to achieve fast settling
characteristics (6 ns Typ.). By integrating
the sample-and-hold circuit, it became
possible to assure a fully adequate
sampling margin even in the narrow sampling
interval in 8×-speed Blu-ray Disc
recording. (See figure 7.) |
|
 |
 LDD |
|
See
all articles with figures and tables.  |
|
Vol.50 |
|
