Optical Pickup Device that Achieves 8××-Speed Blu-ray Recording and Playback
The Industry’s Highest Level of Low-Noise and High-Speed Performance
Breaking the Technological Barriers to 8××-Speed Blu-ray Recording and
Playback
RF/Servo (PDIC)
■ Built-in wideband (230
MHz) I-V amplifier
■ Low noise (-4.4 dB at 176
MHz compared to current products)
■ Multi-stage gain switching (IV: 8 stages)
■ High-sensitivity photodetector (0.3 A/W at 405
nm)
Power Monitor (PDIC)
■ Rapid settling: 6 ns (Typ.)
■ Wide-range gain adjustment function (differential
gain: 0.24 to 44.4 V/mW)
■ Built-in sample-and-hold
circuit
Blu-ray Discs are used in a wide range of
products including recorders, PCs, and
games, and the popularity of this technology is expected to increase rapidly. To
realize the potential of the Blu-ray Disc
even further, Sony is continuing development efforts aimed at achieving recording and playback at Blu-ray Disc speeds
of 8× and higher and at achieving even
higher recording capacities through even
higher layer counts in multilayer Blu-ray
Disc media. Improving the performance
of the optical pickup (OP) is critical to
achieving these goals and in particular,
the photodetector IC (PDIC) and laser
diode driver (LDD) mounted in the OP
hold the key to these improvements. To
achieve 8× Blu-ray Disc recording and
playback, two or more times the bandwidth of existing 16× DVD recording and
playback OPs and even lower noise are
required. This is extremely difficult for
current device and circuit technologies.
To resolve these Blu-ray Disc issues,
Sony has developed a new BiCMOS pro-
cess for PDICs and has achieved both low
noise and fast response times. By increasing the compatibility with the PDIC while
at the same time increasing the performance of the LDD as well, Sony has proposed a new architecture for 8×-speed
Blu-ray Disc recording and playback.
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
Disc
■ Serial interface
RF/SERVO
PDIC
Laser Diode Driver (LDD)
LD
Power monitor
PDIC
LDD
<Optical pickup>
■ Figure 1 Optical Pickup Structure Overview
Input Noise (RF)
Input Noise [pA/√Hz]
■ Operating frequency:
16 to 530 MHz
■ Minimum 59 ps (1/32T)
resolution
■ Built-in write strategy
■ Sampling pulse output
for external sample-andhold function
■ Maximum drive current
BD: 550 mA, CD/DVD:
1000 mA
10
9
8
7
6
5
4
3
2
1
0
Current (Sony)
New (Sony)
–4.4 dB
0
50
100
Frequency [MHz]
■ Figure 2 Noise Characteristics Comparison
150
200
laser automatic power control (APC) system. This device directly monitors the
laser output and monitors the laser power
during reading and writing.
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)
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,
Power Monitor Total Gain
Frequency Response (RF output)
50
+3
Sensitivity [V/mW]
New (Sony)
Current (Sony)
Gain [dB]
0
fc = 230 MHz
–3
–6
40
Mode EH
30
20
10
100
Frequency [MHz]
1000
0
64
Fall Response
2.0
1.8
1.8
1.6
1.6
1.4
Output Voltage [V]
Output Voltage [V]
Rise Response
Sony new
1.2
Sony current
1.0
0.8
0.6
1.4
1.2
1.0
0.8
0.4
0.2
0.2
0.0
+10
+15
Time [ns]
■ Figure 5 Power Monitor Response Waveforms
+20
Sony current
0.6
0.4
+5
192
■ Figure 4 Gain Adjustment Range
2.0
0
128
Gain Setting [dec]
■ Figure 3 Frequency Characteristics Comparison
0.0
–5
Mode H
Mode M
Mode L
10
0
–9
1
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 highspeed settling performance (8 ns, Typ.)
required for 8×-speed Blu-ray Disc recording while transmitting over a flexible
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).
Sony new
–5
0
+5
+10
Time [ns]
+15
+20
Current
adjust range
256
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.)
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 sampleand-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.)
LDD
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.)
S/H pulse
GCA
P
VoutP
N
VoutN
Sampling pulse 1ns
Power monitor
internal out
S/H
IV
20 ns
20 ns
Sampling pulse delay
Test pattern
Integration of the
Multi-stage external variable
resistor
circuit
Addition of a
sample-and-hold
circuit
New S/H Response
2.0
Sampling pulse width = 1ns
1.8
■ Figure 6 Power Monitor Structure
1.6
4T
2T
2T
NRZI data
2T
3T
Output Voltage [V]
1.4
New
1.2
1.0
Settling time: 6 ns
0.8
Sampling region
0.6
Write strategy
0.4
0.2
Optical input
0.0
–5
0
■ Figure 8 Write Strategy Example
■ Figure 7
+5
+10
+15
Sampling Pulse Delay [ns]
+20
+25
Sample-and-Hold Characteristics Evaluation
Test pattern
Future Developments
Sony has proposed devices for use in optical pickups that can achieve 8×-speed
Blu-ray Disc recording and playback.
Keep your eye on Sony for PDIC and
LDD devices that can support higher capacities through increased Blu-ray Disc
recording and playback speeds and multilayer media.
(1) APC Sampling
Main board
OP
8T@BD × 8 = 15.15 ns
NRZI data
RF amplifier
FM-PDIC
APC
(1)
Space sampling
Power monitor
Flexible cable transmission
and circuit delay
Read APC
S/H
Power monitor
waveform
Mark sampling
Current LDD
S/H
Power control
Current
amplifier
DSP
(2)
Current
SW
The sampling gate cannot be opened
Sampling pulse
(2) Timing Pulse Transmission
Timing
gen.
Write strategy
Variations in the
amount of delay
Write APC
Data/clock
Write
strategy
NRZI data
4T
2T
2T
2T
3T
Write strategy
Flexible flat cable
(FFC)
LVDS waveform
Edge displacement due to inter-code
interference in the shortest pulses.
× -Speed Blu-ray Disc Operation
■ Figure 9 Problems with Existing Architectures for 8×
OP
FM-PDIC
<2> APC sampling internally in the FM-PDIC that
takes advantage of a new process technology
The shortest is roughly 1T
(1.88 ns)
Main board
RF amplifier
Space sampling
APC
S/H
Mark sampling
Power monitor
File Vertical Timebase Trigger Display Cursors Measure Math Analysis Utilities Help
S/H
Sampling pulse
WS-LDD
Current
amplifier
Current
SW
<3> Power control based on a
specified voltage that follows
the existing APC system.
Power control
DSP
C2
Timing
gen.
Write
strategy
Data/clock
<1> Achieving both the complex WS patterns expected for 8×-speed
Blu-ray Disc recording and reduction in power consumption to a
practical level through revision of the WS architecture
Write
strategy
Data/clock
C2
DC50
100 mV/div
50.0 mV ofst
Timebase
1.72 ns
RIS
500 ps/div
1.00 kS
200 GS/s
Trigger
Stop
Edge
C2
0 mV
Negative
LeCroy
■ Figure 10 Product Concepts for a Built-in Write Strategy LDD that Achieves
×-Speed Blu-ray Disc Operation
8×
■ Figure 11 8×
×-Speed Blu-ray Disc:
59 ps Timing Resolution