Optical recording and reproduction

OPTICAL RECORDING AND REPRODUCTION
Audio Disc - Processing of the Audio signal - read out from the Disc
Reconstruction of audio signal - Video Disc – Video disc formats - recording
systems - Play back Systems, CD player and DVD player, Blue ray discs.
Text books
1. S.P.Bali, ―Consumer Electronics‖, Pearson Education, 2005.
2. Jochen Schiller, ―Mobile Communications‖, 2nd Edition, Addison-Wesley, 2001.
Reference Books
1. William Stallings, ―Wireless communications and Networks‖, 2nd Edition, Pearson
Education Asia, 2000.
2. R.R.Gulati ,‖Monochrome and colour television‖ , New age International Publisher, 2010
 Compact disc (CD) players are a very specialized form of phonograph, record player,
or tunable.
 A CD player plays pre-recorded discs (carrying music, speech, etc.) through a
conventional hi-fi or stereo system (amplifier and loudspeakers). The disc is single -
sided, 4.75 in (120 mm) in diameter, and can contain up to 60 min of hi-fi stereo
sound.
 The compact disc spins at a high rate of speed compared with a conventional audio
record, and uses a light beam/optical pick-up instead of the standard stylus/needle
pick-up arm.
 In addition to superior sound can provide immediate access to audio at any part of
the disc. It is also possible to program CD players to play only selected portions of
the audio.
 In the Laser Vision System, Fig.1 (a), which records video information, the signal is
recorded on the disc in the form of a spiral track that consists of a succession of pits.
The intervals between the pits are known as lands. The information is present in the
track in analog form.
 Each transition from land to pit and vice versa marks a zero crossing of the
modulated video signal. On the compact disc, Fig.1 (b), the signal is recorded in a
similar manner, but the information is present in the track in digital form.
Fig.1 (a) Details of Laser Vision system showing the optical pickup and the disc
microstructure and (b) Compact discs
3.1 AUDIO DISC

 Each pit and each land represents a series of bits called channel bits. After each
land/pit or pit/land transition there is a 1 and all the channel bits in between are 0.
 The density of the information on the compact disc is very high; the smallest unit of
audio information (the audio bit) covers an area of 1 μm2 on the disc, and the
diameter of the scanning light spot is only 1μm. The pitch of the track is 1.6μm the
width 0.6μm and the depth 0.12μm.
 The minimum length of a pit or the land between two pits is 0.9μm, the maximum
length is 3.3μm. The side of the transparent carrier material T in which the pits P are
impressed, the upper side during playback if the spindle is vertical, is covered with a
reflecting layer R and a protective layer P The track is optically scanned from below
the disc at a constant velocity of 1.25 m/s.
 The speed of rotation of the disc therefore varies from 8rev/s to about 3.5rev/s (or
480 rpm to about 210 rpm).
Fig. 2(a) Cross-section through a compact disc in the direction of the spiral track b) I
the intensity of the signal read by the optical pickup plotted as a function of time
 Electric recording, introduced in the 1920s, made this operation more complicated by
converting the acoustic signal to an electrical signal both in making the recording and
in playing it back. (See Fig. 3.)
 The vital advantage was that electrical signals, unlike acoustic signals, could easily
be amplified.
 The basic operation of a CD player is almost as simple.
 The electrical signal is converted from a continuously varying waveform to a
sequence of Binary digits, 0s and 1s.
 These are then recorded on a spiral path around the disk. (See Fig.4)
 There are pits or "dimples" in the track, and the falling and rising edges of a dimple
correspond to the falling and rising edges of the pulse train. In playback a laser beam
tracks the spiral path. Where there are height changes, the beam is not reflected
sharply, but attenuated.
3.2 Processing of the Audio signal

Fig. 3 Digital sound recording
Fig. 4 Digital sound recording
 A light sensor detects the reflections, producing again the sequence of 0s and 1s,
which is then converted back to an analog sound signal
 CD players provide better sound than conventional record players: increased
bandwidth (a lower bound of 20 hertz rather than 30 hertz), flatter frequency
response curve (plus or minus 0.5 decibels rather than 3 decibels), greater dynamic
range (90 dB rather than 70 dB), better signal to noise ratio (90 dB rather than 60
dB), much smaller harmonic distortion (0.01 percent rather than 1 to 2 percent), and
much better separation between the two stereo channels (90 dB rather than 30 dB)
 Other advantages are smaller size, longer playing time, and greater durability (there
being no mechanical contact in playback to cause wear of the disks)
 In addition, one has immediate access to different tracks, and programmed play is
possible. Finally, CDs are almost immune to the dust, scratches, and fingerprints that
disturb the sound of LPs.
 It is not, then, surprising that in less than a decade after their introduction in the early
1980s, CD players drove record players from the market
 While the vital advantage of electric recording was that it permitted amplification, the
vital advantage of CD recording is that it permitted many types of signal processing,
which confer the advantages just named.

 The electron tube made amplification possible; microelectronics made complex, real-
time signal processing possible. One of the most important of the signal processing
tasks is the conversion of the signal from analog to digital form, which is done in such
a way that the original waveform can be recreated with a high degree of accuracy.
 The digital encoding itself confers an important advantage: slight imperfections in the
disk or low levels of electrical noise in the digital circuits-ones small enough not to
change a 0 into a 1 or vice versa-no degradation of the signal at all.
 Errors inevitably occur, but the signal processing capability of the CD player can
usually correct them. First, there is redundancy in the digital coding so that if a small
number of bits are misread, the original sequence is automatically restored.
 Second, successive binary digits are not recorded together, but physically separated.
This means that if a defect in the disk affects a large number of bits, these will be
drawn from different sampling areas of the original signal.
 Thus, a dust particle, a scratch, a fingerprint, or even a small hole through the disk
will not affect the sound. Finally, larger errors, which the program cannot fully correct,
are detected and minimized through digital filtering.
 The analog signal from the microphone into a digital signal, pulse-code modulation
(PCM) is used. In this system the signal is periodically sampled and each sample is
translated into a binary number.
 From Nyquist sampling theorem the frequency of the sampling should be at least
twice as high as the highest frequency to be accounted for in the analog signal. The
number of bits per sample determines the signal-to-noise ratio in the subsequent
reproduction.
 In the compact disc system the analog system is sampled at a rate of 44.1 kHz,
which is sufficient for the reproduction of the maximum frequency of 20 kHz. The
signal is quantized by the method of uniform or linear quantization, the sampled
amplitude is divided into equal parts.
 The number of bits per sample (these are called audio bits) is 32; i.e. 16 for the left
and 16 for the right audio channel. This corresponds to a signal-to-noise ratio of more
than 90dB. The net bit rate is thus 44.1 × 103 × 32 or 1.41 × 106 audio bits per
second.
 The audio bits are grouped into frames, each containing six of the original samples.
Successive blocks of audio bits have blocks of parity bits added to them in
accordance with a coding system called Cross-Interleaved Reed-Solomon Code
(CIRC).
Fig. 5 The information on the compact disc is recorded form as a spiral track consisting
of a succession of pits
 This makes it possible to correct errors during the reproduction of the signal. The
ratio of the number of bits before and after this operation is 3:4. Each frame then has

Control and Display (C & D) bits added to it; one of the functions of C & D bits is
providing the information for the listener. After this operation the bits are called data
bits.
 Next, the bit stream is modulated, that is to say the data bits are translated into
channel bits which are suitable for storage on the disc. The Eight-to-Fourteen
Modulation (EFM) is used for this purpose.
 In EFM code blocks of eight bits are translated into blocks of fourteen bits. The
blocks of fourteen bits are linked by these merging bits.
 The ratio of the number of bits before and after modulation is thus 8: 17. The
information on the compact disc is recorded in digital form as a spiral track consisting
of a succession of pits.
 The pitch of the track is 1.6μm, the width 0.6μm and the depth of the pit 0.12μm. The
length of a pit or the land between two pits has a minimum value of 0.9μm and a
maximum value of 3.3μm.
Table 1. Names of the successive signals, the associated bit rates and operations during
the processing of the audio signal
Name
Bit rate in 106
bits/s
Operation
Audio signal PCM(44.1KHZ)
Audio bit stream 1.41 CIRC + (parity bits); Addition of C & D bits
Data bit stream 1.94 EFM; Addition of merging bits
Channel bit stream 4.32 Addition of synchronization patterns
 The disc is optically scanned in the player. This is done by AlGaAs semiconductor
laser figure shows the optical part of the pickup.
 The light from the laser La (wavelength 800 nm) is focused through the lenses L2
and Ll onto the reflecting layer of the disc. The diameter of the light spot S, Fig. 4, is
about 1μm. When the light falls on an interval between two pits, the light is almost
totally reflected and reaches the four photodiodes D1 to D4 via the half-silvered
mirror M.
 When the spot lands on a pit—the depth of a pit is about 1/4 of the wavelength in the
transparent substrate material interference causes less light to be reflected and an
appreciably smaller amount reaches the photodiodes.
 When the output signals from the four photodiodes are added together the result is a
fairly rough approximation to the rectangular pulse pattern present on the disc in the
form of pits and intervals.
Readout from the disc

Fig. 6 Diagram of the Optical pick - up
Fig. 7 CD player

Fig. 8 The optical pick-up
 The optical pick-up Fig.4 shown in above, is very small (about 45 × 12 mm) and is
mounted in a pivoting arm that enables the pick-up to describe a radial arc across the
disc, so that it can scan the complete spiral track.
 Around the pivotal point of arm is mounted a linear motor that consists of a
combination of a coil and a permanent magnet. When the coil is energized the pick-
up can be directed to any required part of the track, the locational information being
provided by the C & D bits added to each frame on the disc.
 The pick-up is thus able to find independently any particular passage of music
indicated by the listener. When it has been found the pick-up must then follow the
track accurately to within ±0.1μm without being affected by the next or previous track.
 Since the track on the disc may have some slight eccentricity, and since also the
suspension of the turntable is not perfect, the track may have a maximum side-to-
side swing of 300 μm.
 A tracking servo system is therefore necessary to ensure that the deviation between
pick-up and track is smaller than the permitted value of + 0.1μm and in addition, to
absorb the consequences of small vibrations of the player. The tracking-error signal
is delivered by the four photodiodes D1 to D4.
 When the spot S, seen in the radial direction, is situated in the centre of the track, a
symmetrical beam is reflected. If the spot lies slightly to one side of the track,
however, interference effects cause asymmetry in the reflected beam.
 This asymmetry is detected by the prism P2, which splits the beam into two
components. Beyond the prism, one component has a higher mean intensity than the
other.
 The signal obtained by coupling the photodiodes as (D1 + D2) – (D3 + D4) can
therefore be used as a tracking error signal.

 The signal read from the disc by the optical – pickup has to be reconstituted to form
the analog audio signal.
 Fig.9 shows the block diagram of the signal processing in the player
Fig.9 Block diagram of the signal processing in the player
 D, input signal read by the optical pick – up. A, the two output analog audio signals
from the Left (L) and the Right (R) audio channels
 Demodulation circuit in ERCO, error correction circuit.
 Buffer, buffer memory forming part of the main memory , Memory associated with
ERCO
 CIM (Concealment, Interpolation, Masking) circuit, in which errors that are only
detected since they cannot be corrected are masked or concealed. F, filters for
interpolation, DAC, Digital - to - analog conversion circuits. Each of the blocks
mentioned here are fabricated in VLSI technology, C, Clock generator controlled by a
quartz crystal
 The degree to which buffer memory capacity is filled serves as a criterion in
controlling the speed of the disc. In Demod the demodulation follows the same rules
that were applied to the EFM modulation, but now in the opposite sense.
 The information is them temporarily stored in a buffer memory and then reaches the
Error detection and Correction (ERCO). The parity bits can be used here to correct
errors, or just to detect errors if correction is found to be impossible.
 These errors may originate from in the manufacturing process, damage during use,
or finger marks or dust on the disc.
 Since the information with the CIRC code is interleaved in time, errors that occur at
the input of ERCO in one frame are spread over a large number of frames during
decoding in ERCO
3.3 Reconstitution of the audio signal

 This increase the probability that the maximum number of correctable errors per
frame will not be exceeded. A flaw, such as a scratch, can often produce a train of
errors called an error burst
 The error – correction code used in ERCO can correct a burst of about 4000 data
bits, largely because the errors are spread out in this way. If more errors than the
permitted maximum error, they can only be detected
 In the CIM block, the errors detected are then masked, if the value of a sample
indicates an error, a new value is found by linear interpolation between the preceding
values and the next one. If two or more successive sample values indicate an error,
they are muted (made equal to zero).
 At the same time a gradual transition is created to the values preceding and
succeeding it by causing a number of values before the error and after it to decrease
to zero in a particular pattern.
 In the digital-to-analog convertor (DAC) the 16bit samples first pass through
interpolation filters F and are then translated and recombined to re-create the original
analog signal A from the two audio channels L and R
 Since samples must be recombined at exactly the same rate as they are taken from
the analog audio signal, the DAC‘s and also CIM and ERCO are synchronized by a
clock generator , C, controlled by a quartz crystal
 Fig.7 also illustrates the control of the disc speed nD. The bit stream leaves the buffer
memory, however , at a rate that depends on the speed of revolution of the disc, the
extent to which nD and the sampling rate are matched determines the filling degree
of buffer memory
 The control is so arranged as to ensure that the buffer memory is at all times filled to
50% of its capacity. The analog signal from the player is thus completely free from
wow and flutter, yet with only moderate equipment‘s for the speed control of the disc
3.4.1 Evolution of Video Disc
 The concept of gramophone record that produces pictures first became a reality in
1920‘s, long before the development of the first video disc cassette.
 John Logie Baird successfully created a mechanical television system by recording
simple visual signals on an ordinary 78RPM gramophone record and in 1935 his
invention went on sales in Selfridges.
 Purchases of Baird‘s video disc were able to view various British public figures in
profile. The invention failed to capture the imagination of the public and was
eventually withdrawn.
 It was 35 years before the first video disc appeared but it was never actually
launched on the British market.
 It was supposed to be marketed by a company called Teldec, jointly by the German
company Telefunken and Decca in the U.K. Made of plastic and with a playing time
of only ten minutes the disc was named TeD; however due to a mixture of technical
problems and disagreement between Teldec partners, it never became commercially
available.
3.4 VIDEO DISC

 The Teldec debacle, however, set the video disc ball rolling, prompting a burst of
activity from the electronic companies around the world as they attempted to improve
upon the original idea.
 Philips was the first off the mark unveiling its video disc at a press conference in
Eindhoven in 1972. It has taken the company another ten years to introduce the first
commercially available video disc and video disc player in the U.K.
3.4.2 Introduction
 The pioneer and Philips video disc resembles very much in its physical shape of a
gramophone record
Fig.10 Video disc
 In Fig.10 it consists of a transparent plastic material with standardized diameters of
30 cm and 20 cm and a thickness of 1.1 mm.
 The most striking differences with an audio record are its mirror like appearance due
to a reflective coating and the fact that it can be played on one side only. The basic
difference lies in the structure of information.
 Whereas the audio disc has grooves, the walls of which are modulated with an audio
signal, the video disc, in view of the requirements of a much higher information
density, has tracks with a much higher information density, has tracks with a much
finer information and with a spacing that is about 60 times smaller than that of the
audio disc.
 Two basic types of disc are available, one rotating at 1800r.p.m for areas with NTSC
television system and another rotating at 1500RPM for areas with PAL or SECAM
television system. The information on the disc exists as a spiral track starting at the
inside of a fixed diameter and moving to the outside.
 Average track pitch is 1.6µm, resulting in a playtime time of approximately 30
minutes for a 30 cm diameter disc. The information in the track consists of small
depressions called pits with variable distance and length. Pit width is 0.4 µm,
whereas pit depth is approximately 0.1µm
 Instead of depressions, other elements suitable for absorption and dispersion of light
can also be used and exist mainly as a result of mastering system used.
 The total track length on a 34 cm disc about 34 km and the linear speed of tracking
varies from 37 km/hr at the innermost track to 100 km/hr at the outermost track. One
complete television picture (two fields) requires a surface area on the disc of 0.5 mm
at the innermost track.

 In general, Video disc was a mechanical video disc system developed in Japan by
Matsushita Subsidiary National Panasonic. The 12 inch vinyl disc was spun at 500
rpm with each revolution holding three frames of color video, with a total of up to an
hour of video on each side of the disc.
 Discs could be recorded in either 30 minutes per side format, or 60 minutes per side
format. A later incarnation of the system used 9 inch discs in caddies capable of
storing 75 minutes per side.
 Thomson CSF created a system that used thin flexible video discs, which used a
trans missive laser system, with light source and pick up on opposite sides of the
disc. The system was marketed for Industrial and Educational use in 1980.
 Each side of the disc could hold 50,000 still CAV frames, and both sides could be
read without removing the disc. Thomson exited the videodisc market in 1981. RCA
produced a system called CED under the brand Selecta Vision in 1981. The system
used a physical pickup riding in grooves of a pressed disc, reading variance in
capacitance in the underlying disc.
 The system competed with Laserdisc for a few years, before being abandoned. JVC
produced a system very similar to CED called Video High Density; it was launched in
1983 and marketed predominantly in Japan.
 It was a capacitance contact system but without grooves. VHD discs were adopted in
the UK by Thorn EMI which started to develop a consumer catalogue, including
bespoke Material.
 Development for the mass market was halted in late 1983 but the system remained
on sale for educational and business markets as a computer controlled video system
until the late 1980s, with very little success.
 DVD (Digital Video Disc, or Digital Versatile Disc) was released in 1996. It is a hybrid
of Philips and Sony's MM-CD (Multi-Media Compact Disc) format and Toshiba's SD
(Super Density) format.
 The last-minute adoption of the hybrid DVD format was agreed to by all three
companies in an effort to avoid a damaging format war, similar to that between Beta
and VHS in the 1970s and 1980s. Toshiba failed to reach a similar compromise
agreement with Sony in the race to develop a high-definition optical video disc format
in the 2000s.
 This proved to be a costly mistake for Toshiba (and the format's co-developers, NEC
and Microsoft), and the AOD (Advanced Optical Disc) format, later renamed HD
DVD, lost a brutal format war with Sony's Blu-ray Disc (BD) format.
3.5.1 Classification
 Video discs can be classed based on their playback mechanism:
 Mechanical
 Phonovision
 Phonovid
 Ted
 Disc
 Capacitance Based
 CED,VHD
3.5 VIDEO DISC FORMATS

 Optical discs
 Reflective
 Laserdisc, CD, DVD, Blu-ray, etc.
 Trans missive
 Thomson CSF system
 Laser film
 The three non-interchangeable video disc formats fall into two basic categories;
optical and capacitance. The laser optical system (also called VLP) which is
employed by Philips uses a laser beam to recover the electronically encoded
information stored on the disc.
 The capacitance system (also called capacitance electronic disc or CED), employed
by both JVC and RCA, uses a stylus and tracking arm similar to that of a
conventional record player to recover the information recorded on the grooves of the
disc.
 There are two variations of the laser optical system reflective and trans missive.
 There are also two variations of the capacitance system, the video/audio high density
system (VHD) and the capacitance electronic disc system (CED).
Fig. 11. The upper half of this diagram shows the tracks of pits, while the lower half
shows a cross section of the disc indicating how the information pits are protected by a
transparent protective coating
 The upper half of this diagram shows the tracks of pits, while the lower half shows a
cross-section of the disc indicating how the information pits are protected by a
transparent protective coating.

 In the optical video disc there is a single information track in which all the information
is stored for the reproduction of a colour television program with two sound channels
and data signals.
 The nonlinearity of the master recording process limits the choice of possible
encoding techniques and a two-level signal recording was found to be the most
attractive solution.
 On this track the information is enclosed in the length and the spacing of the pits or,
in other words, for a rotating disc in the repetition frequency, determined by the
average length of the pits, and a pulse width modulation of the frequency, determined
by the modulation of the length of the pits,
 Fig. The composite video signal employed in the video disc system is frequency
modulated on a carrier at 8MHz which is pulse width modulated by two hi-fi audio
channels at 2.3MHz and 2.8MHz
 Fig shows the block diagram of the signal processing for coding the video and audio
system. Before FM modulation of the video signal pre-emphasis time constants of
50μs and 12.5 μs are employed. The audio signals are FM modulated on carriers of
2.3 MHz and 2.8 MHz with a frequency deviation of + 100 kHz and a pre-emphasis of
75μs.
Fig.12 Video disc recording system
3.6 VIDEO DISC RECORDING SYSTEMS

Fig.13 Signal processing - Encoding
 The two audio carriers are summed with the FM carrier and after limiting, the output
signal is used to modulate the intensity of a laser beam passing through an electro-
optical modulator in the master recording machine.
 The spectrum of video and audio signals is given in Fig. The master is used as a
starting point for the production of discs.
 In reading back the information, the reflected light returning from the disc falls on a
photodiode and its output is amplified and corrected according to the frequency
characteristic of the player.
 A high-pass filter separates the video information and the filters have a crossover
frequency at 3.5MHz
 The separated FM signals are then demodulated and a de-emphasis is applied to
compensate for the pre-emphasis employed before recording, in order to achieve a
better S/N ratio and a more uniform frequency response.

3.7 PLAYBACK SYSTEMS

Fig. 14 Signal processing—decoding
Fig. 15 The spectrum of video and audio signals. Black level is at 8.0 MHz white level at
9.2 MHz.
3.7.1 Introduction
 A Compact Disc (CD) is an optical disc used to store digital data. CD-ROMs and CD-
Rs remain widely used technologies in the computer industry.
 CD-ROM drives employ a near-infrared 780 nm laser diode.
 The laser beam is directed onto the disc via an opto-electronic tracking module,
which then detects whether the beam has been reflected or scattered.
 A CD is made from 1.2 mm thick, almost-pure polycarbonate plastic and weighs 15–
20 grams.
 From the center outward components are at the center (spindle) hole, the first-
transition area (clamping ring), the clamping area (stacking ring), the second-
transition area (mirror band), the information (data) area, and the rim.
 Standard CDs have a diameter of 120 mm and can hold up to 80 minutes of
uncompressed audio (700 MB of data).
 The Mini CD has various diameters ranging from 60 to 80 mm; they are sometimes
used for CD singles or device drivers, storing up to 24 minutes of audio
3.7.2 Construction
 A compact disc is a thin, circular disc of metal and plastic about 12cm (just over 4.5
inches) in diameter.
 Most of a CD is made from a tough, brittle plastic called polycarbonate. The
compact disc consist of polycarbonate substrate 120mm
 The polycarbonate substrate is covered by reflective aluminium or gold to increase
reflectivity.
3.7 CD PLAYER

 The polycarbonate layer contains microscopic pits. Each pit is 100nm in depth &
500nm in width.
 The space between two pits is called lands. The reflective surface is protected by a
layer of lacquer to prevent oxidation.
 CD is shiny on one side and dull on the other and it is important It's shiny so that a
laser beam can bounce off the disc and read the information stored on it.
Fig. 16 CD Layers
3.7.3 Data storage
 The music is recorded on the disc in digital format. A laser actually burns pits into the
plastic representing the 1‘s and 0‘s of the digital data in Fig.17
 These pits are extremely small, about 0.5-μm wide (a micron designated μm is 1-
millionth of a meter). The flat areas between the pits are called lands.
 A binary 1 occurs at a transition from a pit to a land or vice versa while the land is a
string of binary 0‘s. The binary data is recorded as a continuous spiral track about
1.6-μm wide, starting at the center and working outward.
 That is a very efficient way to store the data, but it means that the motor speed must
vary to ensure a steady bit rate when the music is played back.
 The pickup mechanism will experience higher speeds at the center of the disc and
lower speeds at the outer edges of the disc, so that a speed control mechanism
keeps the recovered data rate constant.
Fig. 16 Digital music on a CD is encoded as pits and lands on the CD surface

3.7.3 Parameters
 Scanning velocity: 1.2–1.4 m/s (constant linear velocity) – equivalent to
approximately 500 rpm at the inside of the disc, and approximately 200 rpm at the
outside edge. (A disc played from beginning to end slows down during playback.)
 Track pitch: 1.6 µm
 Disc diameter 120 mm
 Disc thickness: 1.2 mm
 Inner radius program area: 25 mm
 Outer radius program area: 58 mm
 Center spindle hole diameter: 15 mm
3.7.4 Properties of CD
3.7.5 Working
 The music on a CD is derived from two stereo channels of music with a frequency
response from 20 Hz to 20 KHz.
 Digitization occurs at the standard 44.1-kHz rate.
 Each sample is 16-bits long.
 The 16-bit words from the left and right channels are alternated and formatted into a
serial data stream that occurs at a rate of 44.1 kHz × 16 × 2 = 1.4112 MHz
 The 16-bit words are then encoded in a special way.

 First, they undergo error detection and correction encoding scheme using what is
called cross-interleaved Reed–Solomon code (CIRC).
 This coding helps detect errors in reading the disc caused by dirt, scratches, or other
distortion.
 The CIRC adds extra bits that are used to find the errors and fix them prior to
playback.
 Next, the serial data string is then processed using what is called eight-to-fourteen
modulation (EFM).
 Each 8-bit piece of data is translated into a 14-bit word by a lookup table.
 EFM formats the data for the pit-and-land encoding scheme. Finally, the completed
data is formatted into frames 588-bits long and occurring at a rate of 4.32 Mbps.
 That is the speed of the serial data coming from the pickup assembly in a CD player
before processing.
 To recover the audio from the CD, the disc is put into the player and a motor rotates it
in Fig.16 A laser beam is shined on the disc as indicated in Fig.17
 The reflections from the pits and lands produce an optical light pattern that is picked
up by a photo detector that converts the light variations into the 4.32-Mbps bit stream.
 A motor control system varies the speed of the motor to keep the data rate steady.
The data stream goes to a batch of processing circuits.
 First, the EFM is removed, and then a CIRC decoder identifies and repairs any errors
and recovers the original 1.41-Mbps data stream.
 A DE multiplexer separates the left- and right-channel 16-bit words and sends them
to the DACs, where the original analog music is recovered and sent to the power
amplifiers and speakers.
Fig 17. Block diagram of CD player
 The CD can store lots of data. Its capacity is in the 650- to 700-MB range.
 That translates into a maximum of about 74 min of audio. And this is not compressed.

3.7.6 Recording System
 A compact-disc (CD) recording system is described in Fig. 18
 The analog audio signal is sensed from each microphone and then fed to the anti-
aliasing low pass filter.
 Each filtered audio signal is sampled at the industry standard rate of 44.1 kilo-
samples per second, quantized, and coded to 16 bits for each digital sample in each
channel.
 The two channels are further multiplexed and encoded, and extra bits are added to
provide information such as playing time and track number for the listener.
 The encoded data bits are modulated for storage, and more synchronized bits are
added for subsequent recovery of sampling frequency.
 The modulated signal is then applied to control a laser beam that illuminates the
photosensitive layer of a rotating glass disc.
 When the laser turns on and off, the digital information is etched on the
photosensitive layer as a pattern of pits and lands in a spiral track.
 This master disc forms the basis for mass production of the commercial CD from the
thermoplastic material.
Fig 18. Simplified Encoder of the CD Recording system
3.7.7 Playback System
 During playback, as illustrated in Fig. 19, a laser optically scans the tracks on a CD to
produce digital signal. The digital signal is then demodulated.
 The demodulated signal is further oversampled by a factor of 4 to acquire a sampling
rate of 176.4kHz for each channel and is then passed to the 14-bit DAC unit.
 For the time being, we consider the oversampling process as interpolation that is,
adding three samples between every two original samples in this case, as we shall
see in Chapter 11. After DAC, the analog signal is sent to the anti-image analog filter,
which is a lowpass filter to smooth the voltage steps from the DAC unit.
 The output from each anti-image filter is fed to its amplifier and loudspeaker. The
purpose of the oversampling is to relieve the higher-filter-order requirement for the
anti-image lowpass filter, making the circuit design much easier and economical

Fig 19. Simplified Decoder of the CD Recording system
3.7.8 Advantages and Disadvantages
3.8.1 Introduction
 A DVD player is a device that plays DVDs produced under both the DVD-Video and
DVD-Audio technical standards, two different and incompatible standards. Some
DVD players will also play audio CDs.
 DVD players are connected to a television to watch the DVD content, which could be
a movie, a recorded TV show, or other content. The first DVD player was created by
Sony Corporation in Japan in collaboration with Pacific Digital Company from the
United States in 1997.
 Some manufacturers originally announced that DVD players would be available as
early as the middle of 1996. These predictions were too optimistic. Delivery was
initially held up for "political" reasons of copy protection demanded by movie studios,
but was later delayed by lack of movie titles.
 The first players appeared in Japan on November 1, 1996, followed by the United
States on March 19, 1997 (a few days earlier than the DVD-Video launch there) with
distribution limited to only seven major cities for the first six months.
3.8 DVD PLAYER

3.8.2 Properties of DVD
3.8.3 Parts of a DVD Player
 The DVD player is not only used for playing the data present in a DVD, but also to
write the content onto a DVD. As told earlier, DVD‘s have pits and a bump in their
track which holds the information that is required to be played.
 This information can be a video, audio or a mixture of both. When a DVD player
reads this data, the smooth surface is usually taken as a ‗0‘ and pits are usually taken
as a ‗1‘. In order to create as well as read these data, a red laser with a wavelength
of 600 nanometers.
 This is about 180 nanometers lesser than the wavelength of CD, which enables it to
have a higher density of pits. Thus the size of the DVD increases.
 Though the first released DVD‘s were only a single layer, 2 layered discs have been
released nowadays. Single layer can hold only up to 4.7 GB of data while double
layered DVD can hold up to 17 GB of data.
 The DVD design is similar to a CD a reflective silver layer in the centre and a semi-
transparent gold layer on the top of it. A DVD does not have the capacity to hold hi-
def movies. So a MPEG-2 compression system is introduced.
 As this is used, the data will be encoded onto the DVD as elements of the changing
frames. This has to be successfully decoded and decompressed by the DVD player.

Thus the parts of a DVD player are
1. Disc drive mechanism
 The disc drive mechanism consists of a motor that will drive the disc in a circular
motion.
 The mechanism will also have a disc feed – a loading tray that is used to accept the
DVD from the user.
 Thus the entire disc drive is basically a spindle that holds the disc and a motor that is
used to circle the disc.
 The spindle is held in its position with the help of small gears and belts that are
attached internally.
 Some players have an automatic feed system in which, there will be no tray.
 Instead the disc will be automatically recognized after inserting a part of it.
2. Optical system
 The optical system mainly consists of the laser beam, lenses, prism, photo-detectors
and also mirrors.
 The output of this mechanism will be the input for the disc-drive.
 The laser beam will be a red laser diode which works at a wavelength of 600
nanometers. The optical system also requires a motor to drive it.
 The laser system and photo-detector is placed together on a single platform.
 The laser diode as well as other diodes is made with the help of glass.
3. Printed Circuit Board
 The PCB is similar to that of any other electronic circuits.
 The electronic outline must be drawn on the PCB with the correct placement of all the
IC‘s resistors as well as capacitors.
 After the outline has been drawn, the components must be soldered to their
respective places.
 All this must be done in a very clean environment so that the board does not become
contaminated by dust.
 All the primary components of the electronic circuit should be made out of silicon.

3.8.4 Working of a DVD Player
Fig 17. Working principle of DVD player in Silver layer
Fig 18. Working principle of DVD player in Gold layer
 The pits and bumps in the DVD are hit by the laser from the optical mechanism of the
DVD player.
 This laser will be reflected differently according to the change of pits and bumps.
 Though the laser hits a single spot, the DVD moves in a circular motion so that the
entire area is covered. Mirrors are also used to change the spot.
 These reflected laser beams are then collected by a light sensor (eg. photo-detector)
which converts the different signals into a binary code.
 In short, the optical system helps in converting the data from the DVD into a digital
code.
 The binary signal is then sent to a Digital to Analog converter which will be setup in
the PCB. Thus the corresponding analog signal of the DVD is obtained.
 The PCB also has amplifiers which amplify the signal and then sends it to the graphic
and audio systems of the computer/TV. Thus, the corresponding audio/video signal is
obtained.

The basic working of a DVD player is shown below.
Fig.19 Working of DVD Player
3.8.5 Assembling a DVD Player
 As the different parts of the DVD player are all complicated electronic circuits, they
are all manufactured by different people.
 They are later brought together and assembled at one place.
 During the assembling, the PCB will be connected to the rest of the machine and all
the components are placed in the right positions.
 The whole package is then placed inside an outer plastic housing with a front panel
with the buttons for various operations.
 This DVD player is then sent to a packaging station where they are placed safely
inside boxes along with the respective power cords, operating manual, installing
disks and so on.
 They are then taken by the distributors to various shops and then sold to customers.
3.8.5 Advantages and Disadvantages of DVD Player

3.9.1 Introduction
 The technology for storing data continues to bring us ever-increasing capacity.
 First, there were CD-ROM discs, next the DVD-discs, which increased capacity and
data transfer speed.
 Now blu-ray discs that provide 100 GB of storage.
 They are used in optical jukeboxes or libraries for archiving computer data
 Blu-ray Discs (BD) was introduced by Sony in October 2000.
 Even though this new technology was developed for the consumer market, it also
was capable of handling computer data.
 As a matter of fact, Blu-ray became the standard in both markets.
 In the early days of optical discs, there were other formats such as UDO from
Plasmon and HD DVD jointly developed by Toshiba and NEC.
 Blu-ray discs won the battle of the formats because of the consumer demand for this
type of disc.
Fig.19 Comparison of Blue Laser Disc Technology
 The name Blu-ray Disc is derived from the blue-violet laser used to read and write
this type of disc.
 Because of its shorter wavelength (405 nm), substantially more data can be stored
on a Blu-ray Disc than on the DVD format, which uses a red, 650 nm laser.
 Originally Blu-ray Disc could store 25 GB on each layer, and now they can hold 100
GB.
 They actually compete favorably with tape, costing about the same per megabyte.
 The advantage is that the optical media is archival, lasting for over 50 years.
 A current, single-sided, standard DVD can hold about two-hours of standard-
definition movie with a few extra features. But a high-definition movie, which has a
much clearer image, takes up about five times more bandwidth and therefore
requires a disc with about five times more storage.
3.9 BLU RAY DISC

3.9.2 Building Blu-ray Discs
 Blu-ray discs not only have more storage capacity than traditional DVDs, but they
also offer a new level of interactivity.
 Using the latest consumer Blu-ray systems, users will be able to connect to the
Internet and instantly download subtitles and other interactive movie features.
 By using Blu-ray, it offers :
 Record high-definition television (HDTV) without any quality loss
 Instantly skip to any spot on the disc
 Record one program while watching another on the disc
 Create playlists, Edit or reorder programs recorded on the disc
 Automatically search for an empty space on the disc to avoid recording over a
program
 Access the Web to download subtitles and other extra features
 Discs store digitally encoded data, video and audio information in pits spiral grooves
that run from the center of the disc to its edges.
 A laser reads the other side of these pits- the bumps - to play the movie or program
that is stored on the DVD.
 Unlike current DVDs, which use a red laser to read and write data, Blu-ray uses a
blue laser.
 A blue laser has a shorter wavelength (405 nanometers) than a red laser (650
nanometers).
 The smaller beam focuses more precisely, enabling it to read information recorded in
pits that are only 0.15 microns (µm) (1 micron = 10- 6 meters) long this is more than
twice as small as the pits on a DVD.
 Blu-ray has reduced the track pitch from 0.74 microns to 0.32 microns.
 The smaller pits, smaller beam and shorter track pitch together enable a single-layer
Blu-ray disc to hold more than 25 GB of information about five times the amount of
information that can be stored on a DVD.
Fig.20 DVD Vs Blue- Ray Construction
 Each Blu-ray disc is about the same thickness (1.2 millimeters) as a DVD.
 But the two types of discs store data differently.

 In a DVD, the data is sandwiched between two polycarbonate layers, each 0.6-mm
thick.
 Having a polycarbonate layer on top of the data can cause a problem called
birefringence, in which the substrate layer refracts the laser light into two separate
beams.
 If the beam is split too widely, the disc cannot be read.
 Also, if the DVD surface is not exactly flat, and is therefore not exactly perpendicular
to the beam, it can lead to a problem known as disc tilt, in which the laser beam is
distorted.
 All of these issues lead to a very involved manufacturing process.
3.9.3 Properties of Blu-ray
3.9.4 Blu-Ray Disc Specifications
 BD is present in both single layer and double layer. The single layer Blu-Ray Disc
has a capacity of up to 25 GB and double layer has a capacity of 50 GB. Though this
is a practical storage capacity meant for the present Blu-Ray players, there are BD‘s

that have capacities up to 200 GB. These discs, though not marketed yet, can be
played in any Blu-Ray player without any additional equipment.
 Blu-Ray Disc needs a wavelength of 400 nanometer violet-blue laser for its reading at
different speeds like 4.5 MBPS, 9 MBPS, 18 MBPS, 27 MBPS, 36 MBPS and 54
MBPS.
 Blu-Ray disc can run formats that are encoded in MPEG-4 and MPEG-2.
 BD is used for data storage, playing 1080p HD video and audio, 3-D Stereophonic
and so on.
3.9.5 Read out from the disc
 The Blu-ray disc overcomes DVD-reading issues by placing the data on top of a 1.1-
mm-thick polycarbonate layer.
 Having the data on top prevents birefringence and therefore prevents readability
problems.
 And, with the recording layer sitting closer to the objective lens of the reading
mechanism, the problem of disc tilt is virtually eliminated.
 Because the data is closer to the surface, a hard coating is placed on the outside of
the disc to protect it from scratches and fingerprints.
Fig.21 CD Vs DVD Vs Blue- Ray Writing
 The design of the Blu-ray discs saves on manufacturing costs.
 Traditional DVDs are built by injection molding the two 0.6-mm discs between which
the recording layer is sandwiched.
 The process must be done very carefully to prevent birefringence.
 The two discs are molded.
 The recording layer is added to one of the discs.
 The two discs are glued together.
 Blu-ray discs only do the injection-molding process on a single 1.1-mm disc, which
reduces cost.

 That savings balances out the cost of adding the protective layer, so the end price is
no more than the price of a regular DVD.
 Blu-ray also has a higher data transfer rate — 48 Mbps (megabits per second) —
than today‘s DVDs, which transfer at 10 Mbps.
 A Blu-ray disc can record 25 GB of material in just over an hour and a half.
3.9.6 Formats
 Unlike DVDs and CDs, which started with read-only formats and only later added
recordable and re-writable formats, Blu-ray is initially designed in several different
formats:
 BD-ROM (read-only) – for pre-recorded content
 BD-R (recordable) – for PC data storage
 BD-RW (rewritable) – for PC data storage
 BD-RE (rewritable) – for HDTV recording
3.9.7 Advantages and Disadvantages

Optical recording and reproduction

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