DVD
What is the Full form of
DVD?
The full form of DVD is Digital Versatile Disc. DVD is a
digital optical disc storage format which was developed and invented in 1995
and used to store high-capacity files, such as top-standard videos and movies.
VCDs were standard optical digital storage disks before invention, but DVDs
have higher capacity than compact discs of almost the same size and shape.
The unofficial full name of DVD also existed
and it was named Digital Video Disc. But as DVDs were not merely restricted to
videos, mass technology forums denied this full term. In 1995 Four companies
called Sony, Philips, Sony, Panasonic and Toshiba discovered and developed it.
History of DVD
- The DVD was
first developed to replace VHS tapes but soon became famous as a storage
device.
- In 1972
Audio-CD was established as an entertainment tool.
- In 1993, two types of video disks were developed, the MMCD (Multimedia Compact Disc), and the SD (Super Density).
Categories of DVD
A DVD comes in two different sizes.
- DVD with a
size of 120 mm – Used for software, videos, and operating system storage
and so on.
- DVD with a
size of 80 mm – Used for compact devices such as portable music player
& video camera etc.
DVDs are classified depending on their
operation such as
- DVD-ROM can
be used only for reading, but it cannot be written.
- DVD-R is
used for recording data of any kind.
- DVD-RW is
Readable, writable and can be deleted & rewritten.
Benefits of DVD
- High
capacity storage, for example, 4.7 – 9 Gb.
- Great
quality of sound and picture, so the correct approach to store videos
& audios.
- Relatively
inexpensive, because they are manufactured in mass production.
- Like CD, data can be preserved on both sides of the DVD.
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. To know this process it is essential
to know the basics of a DVD.
As told earlier, DVD’s have pits and bumps 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.
Working of DVD Player
Take
a look at the basic block diagram of how a DVD player works.
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.
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.
