Wednesday, June 27, 2012

The Structure of Recordable CD

Recordable CD can be divided into write once CD and rewritable CD.
The write once CD has two types DVD-R, DVD+R.
The rewritable CD has three types DVD-RAM, DVD-RW, DVD+RW.

DVD-R, DVD-RW, and DVD-RAM are the formats defined by DVD forum.
DVD+R, DVD+RW are the formats made by DVD union. About DVD forum and DVD union; please go to DVD Forum and DVD Union.

i. The Structure of Recordable CD
The following picture shows the structure of recordable CD, here take single side, single layer DVD as an example, which is similar to prerecorded CD, and it is composed by two 0.6mm film base joint together. Paint recording layer onto the film base of prerecord groove, then sputter the reflecting layer. This recording layer is the difference between recordable CD and prerecorded CD. Recording layer is to write in data with function of memory that can store the information for a long time.

• Record Principle
The recording layer uses different materials that can lead to different memory performances.
The write once CD has a recording layer of dye. Dye is made up by Cyanine, Phthalocyanine, Phthalocyanin and AZO some organic compound. AZO dye is a kind of dyes developed by Mitsubishi Chemicals Japan, which is expensive, only the high quality DVD-R disc can use this kind of dyes.

During the write in process of burner, data shall be modulated through 8-16 concoct and converted into channel code. The channel code is two serial figures between 0 and 1 with the format such as 10000...1, of which there are at least two "0", at most ten "0". This group of digit can form switch square wave. The number of "0" indicates the time of switch, "1" is the switch convert signal. The switch square wave control the switch of laser head. When it is under a state of "switch on", the laser head shall give off high power rail which can make dyes gasified and facula formed. This facula is somewhat like the pit in prerecorded CD. It has a low transparency, so the light is a little bit weak through the reflecting layer. The part between two faculae is "land". This "land" is of better translucency, so the light reflected by the land is much stronger. This optical feature is the same as that of the prerecorded CD, so the data can be read by CD-ROM. As we know, the light reflection of land and pit is different. But the laser will output the number 0, only on the joint part of pit and land, it will output 1.The length of land and pit determines the number of 0. All these figures output by laser is actually the channel code of the disc. These channel code shall be processed repeatedly to from the real data. The faculae on the recording layer can not be eliminated after being formed, so the disc can be written in once.

The recording layer of rewritable CD is made in phase change material. DVD-RW and DVD+RW uses the alloy of Ag, In, Sb, TE, while the DVD-RAM uses alloy of GE, Sb, Te. The double layer rewritable CD in development shall use the alloy of Ge, Sn, Sb, Te as the Layer 0 with a thickness of 6 nm and the alloy of Ge,Sn,Sb as the Layer 1 with the size of 12 nm.

The phase change material has two stable statuses: crystalline state and Non-crystalline state. The phase change recording layer is initialized into crystalline state when the DVD-RW is getting off the assembly line. In writing data, the recorder will convert the data into channel code, then square switch wave is formed to control the laser head and the on and off of irradiation. If the switch is on, the laser head shall give off high power radiation that enables the temperature of phase change material surpass its melting temperature and make it melt. As the melt time is shorter than that of crystallization period; the phase change material in the radiation area shall change from the crystalline state into amorphous state as the picture shows. When the switch is off, the phase change material would be stay in a crystalline state, as no laser radiation. In the groove, the reflection rate of crystalline and amorphous state area is different. The crystalline area has a much higher translucency works as the land of prerecorded CD. While the amorphous state is able to prevent light to going through, that works as the pit. This is how the rewritable CD store data.

Another feature of phase change material is reduction which is used in data erasing. While radiating in medium power laser, the temperature of phase change material shall surpass the "crystalline temperature, but not reach the melting temperature, as long as the irradiation time is longer than the crystallization time, it is possible to make the non crystalline change into crystalline. So this feature makes the rewrite of CD possible.

The rewritable DVD has the structure as the below picture shows. There is a layer of heat protection layer both on and below the recording layer. The heat proof layer is to prevent the change of status of phase change recording layer. So the heat proof layer is called Thermal isolation layer, thermal insulating layer.

• Pre-groove
The recording layer of recordable CD is set with grooves that carved in advance, so they are called pre-grooves as the picture shows. The functions of grooves are as following:
1. Tracking. It is to ensure that the laser head can write the data into the groove along the rails.
2. Addressing. It is to ensure the recorder to write in data to the accurate place.
3. Speed. It is to control the driver to rotate at a certain speed and in a certain way.

Wobble: Recordable disc radial grooves are sinusoidal bending mode, showing snake-like. This structure is called wobble. There are two wobble frequency for recordable CD, DVD-R(w) uses 140.6KHz, while the DVD+r (w) uses 817.4 KHz. The wobble loads the information of the recordable CD; it can provide tracking information and speed information. The addressing information veries according to formats.

ATIP (Absolute Time in Pre-groove), which is to concoct the time into the wobble.
ADIP (Address in Pre-groove, which is also to conduct the time code into wobble.

The grooves of DVD-R, DVD-RW, DVD+R and DVD+RW are spiral shaped. The DVD-R and DVD-RW are set with LPP (Land pre pit) with addressing information. DVD+R (W) have a higher wobble frequency than that of DVD-R (W). The addressing information is loaded on the Phase Modulation of groove, so it is also called ADIP.

The rut of pre-grooves DVD-R and DVD-RW is concocted with ATIP and the address information is provided by the LPP. The pre pit shall offer the amplitude peak of the wobble signal of the groove.

The pre-groove of DVD+R and DVD+RW using a ADIP way with information loaded on the phase modulation of the groove.

DVD-RAM has special pre-grooves with a shape of concentric circle. The groove is separated by sector head, the inner circle has molding information area as the left picture shows below. The address information is molded onto the sector head. The most important is that the pit and land can be loaded with data as the right picture shows below.

• Spin mode
There are three spin modes: Constant line Velocity (CLV), Constant Angular Velocity (CAV), Zone constant line velocity (ZCLV).
The DVD-R, DVD-RW use CLV mode, DVD+R, DVD+RW used CLV/CAV mode and DVD-RAM uses ZCLV mode.

ii. The capacity of single side recordable CD
The 120 mm CD has a capacity of 4.7 GB, and 80 mm has a capacity of 1.46 GB.

iii. The rewrite times of CD
The general standard is 1000 times with longevity of 30 years.

iv. Compatibility
DVD-R and DVD-RW can be read on most DVD-ROM.
DVD+R and DVD+RW can not read by common DVD-ROM, they can only read on the DVD-ROM produced by 6c of the DVD Union.
DVD-RM can not be read on common DVD-ROM, it can only be read by DVD-RAM drivers.

v. High-speed recordable CD
At present the high double rate DVD-R has four speeds and eight speeds. DVD-RW has 2 speeds, 3speeds and 5 speeds.
DVD+R have the maximum speed of 16 speeds, while the DVD+RW have the maximum speed of 8 speeds. The following chart is the parameter under high speeds.

Recording time of a 4.7 GB disc

1X-Speed  4.7GB ÷ 11.08Mbps ÷ 60Sec ≈ 57min
2X-Speed  57min ÷ 2 ≈ 28min
4X-Speed  57min ÷ 4 ≈ 14min
8X-Speed  57min ÷ 8 ≈ 7min
16X-Speed  57min ÷ 16 ≈ 3.6min

Bitrate of high speeds DVD-R and DVD-RW

general peremeter 2X DVD-RW 4X DVD-R/RW 8X DVD-R
 basic scanning speed (m/s) 6.98 13.96 27.92
 basic spped channel bitrat (MBPS) 52.32 104.64 209.28
 basic speed user bitrate
22.16 44.32 88.64

Pwer of high speed recording

Recording of upper limit recording erasing
2X DVD-RW 17mW 10mW
4X DVD-RW 28mW 12mW
4X DVD-R 20mW -
8X DVD-R 32mW -

vi. Write once CD and CD-ROM
The following table is the DVD-R, DVD+R, DVD-ROM

Specific parameter DVD-R DVD+R DVD-ROM
 disc type  write once  write once read only
 120mm single layer capacity of the disc (GB)  4.7  4.7  4.7
 recording layer  dye  dye  -
 shape of information layer  spiral wobble groove,
 prewrite pit on land
 spiral phase concoct wobble groove  land and pit
 rail interval (μm)  0.74  0.74  0.74
 reflecting rate  45-85%  45-85%  45-85%
 Burning rotate style  CLV  CLV/CAV  -
 prewrite  yes  no  -

vii. The comparisons between versions of rewritable CD
DVD-RW, DVD+RW, DVD-RAM has its unique advantages. DVD-RW has a better compatibility and easy to be read by DVD-ROM. DVD+RW has some advantages in technology such as its phase concoct, seamless recording, defects management and so on. Moreover, it has a easier way of making. But the disc can not be read by common CD-ROM.DVD-ROM is capable of direct access with fast speed and compatibility with computer system. However, it can only be used on CD-ROM with RAM. Users would like these formats can be unified. It seems a little bit difficult.
Following is the comparison between the three formats of rewritable CD.

specific parameter DVD-RW DVD+RW DVD-RAM
 120mm single layer capacity of disc (GB)  4.7  4.7  4.7
 Laser wave length(nm)  650  655  650
 NA  0.60  0.65  0.60
 shape of prewrite groove  spiral wobble groove,
 prewrite pit on land
 spiral phase concoct wobble groove  concentric wobble groove, grooves cut by sector head
 groove wobble frequency (KHz)  140.6  817.0  140.6
 rail intervals for recording area (μm)  0.74  0.74  0.74
 rotation mode  CLV  CLV/CAV  ZCLV
 address information  pit that plate moulded on the land  cycle wave reverse in groove ADIP  plate moulded sctor head
 recording method  Recording in groove  Recording in groove  recording in goove or on land
 Write/read mode  SEQ  SEQ or Random  Random
 Reflecting rate  18-30%  18-30%  15-25%
 Reading power (mW)  ≤1.0  0.7  ≤1.0
 Erasing power (mW)  8.0-15.0  8.0-15.0  8.0-14.0
 Erasing power (mW)  3.0-8.0  3.0-8.0  3.0-8.0
 Channel code concoct  8-16  8-16  8-16
 ECC  RS-PC(Reed-Solomon Product Code)
 Defect management  Specific software required  Providing 3 reservation area for defect management( In all 4224 sectors) 4 defect management area ( In all 128 sectors)
 Plate moulded Lead-in area  No No  No
 cartridge  No No  bare disc or cartridge disc 

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