CD/DVD TECHNOLOGY

BY:- S.K.Srivastava, DDE, STI(T)

COMPACT DISK

CD system was first introduced in 1980 by a joint venture between Sony and Phillips.

It is the CD that has introduced most people to digital audio reproduction system.

Starting with CD-DA format, CD family was expanded to include CD-ROM(1984),CD-i(1986),CD-WO(1988), Video-CD(1994),

CD-RW(1996) and much more variants with a host of applications in data, audio,video and beyond.

CD-DA sampling freq.- the video route

Professional video recorders were used to prepare CD master tapes as they were the only recorders available to handle large BW requirement of digital audio signal

Therefore, sampling frequency has to correlate with line/field rates of TV standard- storing a few samples per scan line.

CD-DA sampling freq.- the video route …..

NTSC system It uses 525 lines in 30 frames per

second with 490 active lines. With 3 samples/sec, the sampling frequency = 490x30x3=44.1KHz.

PAL system This format uses 625 lines(588 active

lines) in 25 frames/sec.With 3 samples/line, the sampling freq=588x25x3=44.1KHz.

CD.. AUDIO PROCESSING The analog audio signal is converted into digital signal by

Analog to Digital converters with 16 bit linear quantization at a sampling frequency rate

of 44.1 kHz. During recording, first order pre-emphasis may be applied.

Pre-emphasis standards agreed for CD format are 50 and 15 micro seconds. In this case the player must apply a similar de-emphasis to the decoded signal to obtain a flat frequency response.

A specific control code recorded along with the audio signal on the compact disc is used to Inform the player whether pre-emphasis is used and so the player switches on the corresponding de-emphasls circuit.

Moreover, audio information on the CD may comprise four music channels instead of two. This is also identified by a control code to allow automatic switching of players equipped with a four channel play back facility.

Conversion of Analog audio to Digital Signal

CD Cutting

CD cutting is similar to LP record cutting except that the former employs digital technology and uses laser beam for cutting photo resistive material for producing master disc. CD production follows seven main stages as illustrated below:

A glass plate is polished for optimum smoothness. Photo resist coating is applied to its surface. The roughness of glass surface

and the thickness of coating determine the depth of the pit on CD. Photo-resist coating is then exposed to a laser beam, the intensity of which

is acoustically modulated with digitized audio information. The photo-resist layer is developed and then the pits of information are

revealed. The surface is silvered to protect the pits. The surface is plated with nickel to make metal master. The metal master is then used to make mother plates. These mothers are

used to make further metal masters or stammers. The stamping process although named like LP record production, is in fact,

an injection moulding, compression moulding or polymerization process, producing plastic disc.

The signal surface of each disc is then coated with a reflective material (vaporized aluminium) to enable optical readout and further protected with plastic layer, which also support the disc label.

Stages in cutting of a CD..

CD Readout Principle….

CD Readout Principle…

It is evident from the figure that the readout surface is thicker than the label surface.

Therefore, a minor scratch on the readout surface is very well tolerated.

Since the label side lacquer coating is only 30 mm thick, writing on this side is not recommended.

Readout Process…In the readout process, a readout beam is

applied from the opposite side of cutting. The readout beam produces a spot size of

1.2 micro meter at the disc base. Since this beam is applied from the

opposite side of cutting a "pit" is read as a "bump". The beam enters through the largest possible area of the surface approx. 0.7 mm dia circle for a spot size of 1.2 micro meter at the disc base. The size of entry circle is a function of refractive index of the optical system and the thickness of the disc.

Readout process..

Readout Process…

The wavelength of laser beam used for readout of bumps and flats is 780 nm in air.

When light passes through CD medium having refractive index of 1.55; its wavelength is reduced to 500 nm (780/1.55 = 500 nm or 0.5 J.lm).

The height of bump is about λ/4 of laser beam used for readout. While reading CD, the laser spot of 1.2 µm dia moves along the track whose bump width is 0.5 µm and height is 0.13 µm.

When the laser beam traces the bump, the phase of reflected light will be λ/4 apart (bump height = A/4) and hence will cancel out.

When the laser traces the flat, the phases of reflected laser will not change and will add up.

We can say that, there will be no output when laser traces the bump and there will be output when laser traces the flat and thus '1' and '0' are identified.

CD Parameters…

CD Standards

Standards define the way different types of information, such as audio, video or data, are stored on a CD. Currently, there are more than 10 different standards for CDs. Many of these, such as CD-I (Compact Disc-Interactive), were designed for use with proprietary players that combined audio and text or graphics data, and never caught on. The three main formats currently used for audio and data CDs are named for the color of the standards books that describe them.

Red Book Audio The Red Book standard was the original format developed for

storing music on CDs. This standard is also referred to as CD-DA (Compact Disc-

Digital Audio). Audio CDs have the advantage of being playable almost anywhere.

CD Standards…

Yellow Book standard The Yellow Book standard defines how data is

stored on prerecorded CD-ROMS.

Orange Book Standard The Orange Book standard is similar to the Yellow

Book It defines the format for CD-Rs and CD-RWs. MP3

files and other compressed audio formats are simply data files, so they are stored on Yellow Book (pre-recorded) or Orange Book (CD-R and CD-RW) CDs.

What is a CD-RW

A CD-RW is a compact disk, but this can be used again and again like our audio/video tape after erasing the contents.

offers convenience of reuse

Fig. 4: CD-RW

CD-RW--- The technology The technology behind CD-RW is optical phase-change. A CDRW disc's phase-change medium consists of a

polycarbonate substrate, moulded with a spiral groove for servo guidance, absolute time information and other data, on to which a stack (usually five layers) as shown in Fig. Fig. 4: CD-RW 4 is deposited.

The recording layer is sandwiched between dielectric layers that draw excess heat from the phase-change layer during the writing process.

In place of the CD-R disc's dye-based recording layer, CD-RW commonly uses a crystalline compound made up of a mix of silver, indium, antimony and tellurium. This rather exotic mix has a very special property: when it's heated to one temperature and cooled it becomes crystalline, but if it's heated to a higher temperature, when it cools down again it becomes amorphous.

The crystalline areas allow the metalised layer to reflect the laser better while the non-crystalline portion absorbs the laser beam, so it is not reflected.

CD-RW--- The technology…In order to achieve these effects in the recording layer, the CD-Rewritable recorder use three different laser powers:

the highest laser power, which is called "Write Power", creates a non-crystalline (absorptive) state on the recording layer.

the middle power, also known as "Erase Power", melts the recording layer and converts it to a reflective crystalline state.

the lowest power, which is "Read Power", does not alter the state of the recording layer, so it can be used for reading the data.

Read/Write Speed

At 1x speed, a disk spins at about 539 rpm when the head is placed on inner diameter and it slows to 210 rpm at the outer diameter.

At 16x, the speeds are about 8000rpm & 3200rpm.

Real time recorders operate at about 150 kbps rate.

DVD-Digital Versatile Disk It can store more data than

conventional CD’s( 10 times or more) and may eventually supercede the CD, i.e., the future belongs to the DVD’s as this offers more storage capacity than the CD’s.

it uses more advanced technology and four layers.

CDs, CD-RWs and DVD’s employ optical method for reading and writing. Hence, data integrity is less vulnerable as compared to magnetic tapes. They also have a much longer life.

Fig. 5: Multilayer DVDs can store more data

DVD STANDARDS…

DVD+R and DVD+RW

DVD+R and DVD+RW formats are supported by Philips, Sony, Hewlett-Packard, Dell, Ricoh, Yamaha and others.

DVD+R is a recordable DVD format similar to CD-R. A DVD+R can record data only once and then the data becomes permanent on the disc. The disc can not be recorded onto a second time.

DVD+RW is a re-recordable format similar to CD-RW. The data on a DVD+RW disc can be erased and recorded over numerous times without damaging the medium.

DVDs created by a +R/+RW device can be read by most commercial DVD-ROM players.

DVD STANDARDS…DVD-R & DVD-RW These formats are supported by Panasonic, Toshiba, Apple

Computer, Hitachi, NEC, Pioneer, Samsung and Sharp. DVD-R is a recordable DVD format similar to CD-R and

DVD+R. A DVD-R can record data only once and then the data becomes permanent on the disc. The disc cannot be recorded onto a second time. There also are two additional standards for DVD-R disks: DVD-RG for general use, and DVD-RA for authoring, which is used for mastering DVD video or data and is not typically available to the general public.

DVD-RW is a re-recordable format similar to CD-RW or DVD+RW. The data on a DVD-RW disc can be erased and recorded over numerous times without damaging the medium.

DVDs created by a -R/-RW device can be read by most commercial DVD-ROM players.

DVD…DVD+R DL and DVD-R DL Dual layer technology is supported by a range of

manufacturers including Dell, HP, Verbatim, Philips, Sony, Yamaha and others. As the name suggests, dual layer technology provides two individual recordable layers on a single-sided DVD disc. Dual Layer is more commonly called Double Layer in the consumer market, and can be seen written as DVD+R DL or DVD-R DL.

DVD+R DL (also called DVD+R9) is a Dual Layer writeable DVD+R.

DVD-R DL (also called DVD-R9) is a Dual Layer writeable DVD-R. The dual layered discs can hold 7.95GB

The double sided dual layer (called dvd-18) can hold 15.9GB.DVD-ROM DVD-ROM was the first DVD standard to hit the market and is

a read-only format. The video or game content is burned onto the DVD once and the DVD will run on any DVD-ROM-equipped device.

Next Generation DVD’s

The two most prominent competing technologies are Blu-ray and AOD.

Blu-ray Disc (BD) The Blu-ray format was developed jointly by Sony,

Samsung, Sharp, Thomson, Hitachi, Matsushita, Pioneer and Philips, Mistubishi and LG Electronics

It uses a 405nm-wavelength blue-violet laser technology, in contrast to the 650nm-wavelength red laser technology used in traditional DVD formats.

The rewritable Blu-ray disc, with a data transfer rate of 36Mbps (1x speed) can hold up to 25GB of data on a single-layer disc and 50GB on a dual-layer disc.

On a 50GB disc, this translates into 9 hours of high-definition (HD) video or approximately 23 hours of standard-definition (SD) video.

Next Generation DVD …

Advanced Optical Disc (AOD) – AOD was developed jointly by

Toshiba and NEC while Blu-ray has a storage

capacity of 25GB on a single-layer disc, AOD has a storage capacity of 20GB on a single-layer disc. and the capacity to hold 30GB on a dual-layer disc.