Unit II Entertainment Electronics

UNIT II: Entertainment Electronics - Audio systems: Construction and working principle of :
Microphone, Loud speaker, AM and FM receiver, stereo, 2.1 home theatre, 5.1 home theatre.
Display systems: CRT, LCD, LED and Graphics displays Video Players : DVD and Blue RAY.
Recording Systems: Digital Cameras and Camcorders.

Microphones
Microphones are a type of transducer - a device which converts energy from one form to another.
Microphones convert acoustical energy (sound waves) into electrical energy (the audio signal).
Different types of microphone have different ways of converting energy but they all share
one thing in common: The diaphragm. This is a thin piece of material (such as paper, plastic or
aluminium) which vibrates when it is struck by sound waves. In a typical hand-held mic like the one
below, the diaphragm is located in the head of the microphone. When the diaphragm vibrates, it
causes other components in the microphone to vibrate. These vibrations are converted into an
electrical current which becomes the audio signal.

CARBON MICROPHONE
For a telephone system important requirements are (i) the microphone shall be of convenient size;
(ii) capable of mass production at low cost while possessing high sensitivity to operate from a
simple battery; (iii) its performance must be stable and adequate to provide intelligible speech and
articulation and; (iv) it need not necessarily include the higher harmonic frequencies for
reproducing.
The carbon microphone, also known as carbon button
microphone, button microphone, or carbon
transmitter, It consists of two metal plates separated by
granules of carbon. One plate is very thin and faces
outward, acting as a diaphragm. When sound waves strike
this plate, the pressure on the granules changes, which in
turn changes the electrical resistance between the plates.
Higher pressure lowers the resistance as the granules are
pushed closer together. As a steady direct current is
passed between the plates, the varying resistance results
in a modulation of the current at the same frequency of
the impinging sound waves. In telephony, this signal is directly passed through a telephone
system to the central office, or it is electronically amplified in other sound systems, such as a public
address system or a recording device. The frequency response of the carbon microphone, however,
is limited to a narrow range, and the device produces significant electrical noise.
Advantages of Carbon Microphone
1. It delivers high output signal
2. It is simple in construction and rugged in design
3. It's working principle is simple
4. It is cheaper in cost and simple to manufacture.
5. It tolerates extremely high sound pressure levels.

Disadvantages of Carbon Microphone

1. It has high background noise and it will often produce cracking sound. It is not possible to
eliminate this "carbon hiss".
2. It has poor frequency response.
3. It requires battery or other supply for its operation.
4. The carbon granules get damaged and sometimes fused together.
5. As shown it requires amplifier to amplify the signal to be reproduced at the speaker end.
6. Its bandwidth is extremely limited.

Crystal Microphone
The crystal microphone uses the
PIEZOELECTRICEFFECT of Rochelle salt,
quartz, or other crystalline materials. This
means that when mechanical stress is placed
upon the material, a voltage electromagnetic
force (EMF) is generated. Since Rochelle
salt has the largest voltage output for a given

mechanical stress, it is the most commonly

used crystal in microphones. In figure A the
crystal is mounted so that the sound waves
strike it directly. In figure B a diaphragm that
is mechanically linked to the crystal so that
the sound waves are indirectly coupled to
the crystal.
This microphone will have high output in the order of 10 to 100 mV. The crystal microphone is
omni-directional and is cheaper. The disadvantage of crystal microphone is that it is easily damaged
by moisture or heat. This type of microphone is used in cassette recorders. The impedance is very
high usually in the order of 1 to 5 Mega Ohm.

Dynamic Microphone or Moving coil

Dynamic microphones are versatile and ideal for general-purpose use. They use a simple
design with few moving parts. They are relatively strong and flexible to rough handling. They are
also better suited to handling high volume levels, such as from certain musical instruments or
amplifiers. They have no internal amplifier and do not require batteries or external power.

Working Principle

The dynamic or moving coil microphone relies

on the fact that if a wire held within a magnetic
field is moved then an electric current is induced.
This is the same effect as seen in an electric
generator and many other items. The dynamic
microphone consists of a magnet, and a
diaphragm to which a coil is attached. The
assembly is held in place by an outer casing and
the coil can move freely over the magnet.
As sound waves hit the diaphragm, this causes
the coil to move backwards and forwards within the magnetic field and as a result an electric current
is induced in line with the incoming sound vibrations. This EMF is proportional to the velocity of
motion (v) of the conductor in the air-gap: if the microphone is to have the same sensitivity at all
frequencies it is necessary for the velocity of motion of the coil, due to a sound of given intensity, to
be independent of the pitch of the sound.
In order to respond to transients and high frequency sound waves it is necessary to keep the
mass of the cone and its coil as small as possible. For this reason, the coil is usually wound with
aluminium wire of very fine gauge and the number of turns is limited. This means that the generated
voltage is also limited, and so the natural impedance of the instrument is low. The average is around
30 ohm, but many models have a transformer incorporated in the instrument itself to give an output
at a higher impedance.
Advantages of Dynamic Microphone or moving coil microphone

1. It is one of the good quality microphone with omni-directional properties

2. It is available at affordable cost.
3. It is rugged in construction (almost 100% mechanical) and can handle high pressure levels.
4. It does not require any battery or power source to run.
5. It can convert sound waves over entire audible range to electric current (or voltage) for
further use.
6. It is durable which can withstand lot of volume.
7. It colors the sound in the range between 5 to 10 KHz which adds clarity, presence and
understandability to many vocal and instrument sounds

Disadvantages of Dynamic Microphone or moving coil microphone

1. It has poor high frequency response due to inertia of coil, tube & diaphragm and force
required to overcome interaction between coil and magnet. Hence it is not suitable for
recording instruments with higher frequencies and harmonics compare to condenser
microphone.
2. This microphone type miss many sounds as it requires lot of sound pressure to move the
coil.
3. It is not as accurate (or sensitive) as condenser microphone. Hence it cannot be used for in-
studio film productions

Condenser Microphones

Condenser or capacitor, an electronic component which stores energy in the form of an electrostatic
field. The use of condenser micro phone is to convert acoustical energy into electrical energy.
Condenser microphones require power from a battery or external source. The resulting audio signal
is stronger signal than that from a dynamic.
Condensers also tend to be more sensitive and
responsive than dynamics, making them well-
suited to capturing subtle nuances in a sound.
They are not ideal for high-volume work, as
their sensitivity makes them prone to distort.
A capacitor has two plates with a
voltage between them. In the condenser mic,
one of these plates is made of very light
material and acts as the diaphragm. The diaphragm vibrates when struck by sound waves, changing
the distance between the two plates and therefore changing the capacitance. Specifically, when the
plates are closer together, capacitance increases and a charge current occurs. When the plates are
further apart, capacitance decreases and a discharge current occurs.
A voltage is required across the capacitor for this to work. This voltage is supplied either by a
battery in the mic or by external phantom power.
Advantages of Condenser Microphone
1. It is smaller in size, with flat frequency response.
2. It is light in weight compare to dynamic microphone due to lighter diaphragm assembly.
3. It supports high range of frequencies due to fast moving diaphragm.
4. It offers high sensitivity and it is more suitable to capture sounds of audio instruments and
vocals.

Disadvantages of Condenser Microphone

1. It requires voltage (i.e. power) to operate.
2. It can handle certain maximum input signal level.
3. It is more complex compare to dynamic microphone.
4. It is more affected due to extreme temperature and humidity conditions compare to dynamic
microphone.
5. It is more expensive compare to dynamic microphone.
6. Cheaper condenser microphone generates small magnitude of noise.

RIBBON (VELOCITY) MICROPHONES

While ribbon microphones technically

fall under the umbrella of dynamic mics, as
they also transduce acoustic energy through
electromagnetic induction, they are a very
different animal than their rugged, moving-
coil counterparts. In ribbon microphones, A
ribbon of aluminium foil is suspended
between the poles of a magnet and generates
a current when it vibrates within the magnetic
field. There is no multiplication of induced
EMFs by the successive turns of a coil, the
ribbon can be regarded as a coil with but a
single turn. As a result, the output voltage is very low and so also is the impedance, something of
the order of 0.1Ω. All ribbon microphones, therefore, have a built-in transformer to step-up the
impedance and voltage to a usable level.
The ribbon serves as both the diaphragm and the transducer element itself, giving you much greater
sensitivity and transient response in comparison to standard dynamic mics. However, the trade-off
for this increased responsiveness is much greater fragility, as ribbon elements tend to be only a few
microns thick and thus are easily damaged if not cared for properly. Strong gusts of wind and blunt
force impact from drops and falls can all put your average ribbon mic out of commission.
• The ribbon microphone is bidirectional.
• It is more directional than the crystal and dynamic microphones, the overall response of the
ribbon microphone falls off as the angle of sound reaching it varies from 90 degrees to the
faces of the ribbon.

• The ribbon microphone is quite sensitive to the movement of the air surrounding it, and it
must be carefully protected from puffs of wind when used outdoors. A ribbon microphone
should be placed at least 18 inches from the source of the sound.

WIRELESS MICROPHONE:

A wireless microphone, as the name implies, is a microphone without a physical cable

connecting it directly to the sound recording or amplifying equipment with which it is associated.
Also known as a radio microphone, it has a small, battery-powered radio transmitter in the
microphone body, which transmits the audio signal from the microphone by radio waves to a nearby
receiver unit, which recovers the audio. The other audio equipment is connected to the receiver unit
by cable. Wireless microphones are widely used in the entertainment industry, television
broadcasting, and public speaking to allow public speakers, interviewers, performers, and
entertainers to move about freely while using a microphone to amplify their voices.

There are many different standards, frequencies and transmission technologies used to
replace the microphone's cable connection and make it into a wireless microphone. They can
transmit, for example, in radio waves using UHF or VHF frequencies, FM, AM, or various digital
modulation schemes. Some low cost models use infrared light. Infrared microphones require a
direct line of sight between the microphone and the receiver, while costlier radio frequency models
do not.

The advantages are:

• Greater freedom of movement for the artist or speaker.
• Avoidance of cabling problems common with wired microphones, caused by constant
moving and stressing the cables.
 • Reduction of cable "trip hazards" in the performance space
The disadvantages are:
• Sometimes limited range (a wired balanced XLR microphone can run up to 300 ft or 100
meters). Some wireless systems have a shorter range, while more expensive models can
exceed that distance.
• Possible interference with or, more often, from other radio equipment or other radio
microphones, though models with many frequency-synthesized switch-selectable channels
are now plentiful and cost effective.
• Operation time is limited relative to battery life; it is shorter than a normal condenser
microphone due to greater drain on batteries from transmitting circuitry, and from circuitry
giving extra features, if present.
• Noise or dead spots.
• Limited number of operating microphones at the same time and place, due to the limited
number of radio channels.

Characteristics of Microphones
There are many types of microphones available. Each has certain advantages and disadvantages.
Hence the selection of microphones depends upon the certain characteristics as below:
(1) Output level; (2) Frequency response; (3) Output impedance and (4) Directivity.

(1) Output level: -

The output level of a microphone governs the amount of amplification that must be available
for use with the microphone. The output level of microphone is usually given in dB preceded by a
minus sign. The minus sign means that the output level is so many dB below the reference level of
1milliwatt for a specified sound pressure.

(2) Frequency response: -

The frequency response of a microphone is a rating of the fidelity of relative output voltage
which results from sound waves of different frequencies. The simplest way to find a complete
picture of the frequency response characteristics of a microphone is to plot a curve of its output
voltage v/s input frequency. Since good microphones are relatively flat over their range, it is often
considered sufficient to specify the range over which their output does not vary more than ±1-2 dB.
 (3) Output impedance: -
A microphone, like any other component with electrical i/p of o/p, has a value of impedance.
When a microphone is connected to an amplifier, a complete circuit is formed and electric current
flows whenever a sound causes the microphone to generate an electrical voltage.

For most high quality microphones impedance is low, a few ohms ranging upto a hundred
ohms or so. The importance of microphone impedance is not a matter of the precise value but of the
ability of the microphone and the recorder to be matched together. High impedance microphones
must be connected must be connected into a recorder with high impedance input, otherwise both the
signal amplitude and the frequency range will be adversely affected.

Directional Properties
Every microphone has a property known as directionality. This describes the microphone's
sensitivity to sound from various directions. Some microphones pick up sound equally from all
directions, others pick up sound only from one direction or a particular combination of directions.
The types of directionality are divided into three main categories:

1. Omnidirectional
Picks up sound evenly from all directions (omni means "all" or "every").

Captures sound equally from all directions.

Uses: Capturing ambient noise; Situations where sound is coming from many
directions; Situations where the mic position must remain fixed while the
sound source is moving.

Notes:
• Although omni-directional mics are very useful in the right situation, picking up sound from
every direction is not usually what you need. Omni sound is very general and unfocused - if you
are trying to capture sound from a particular subject or area it is likely to be over whelmed by
other noise.

2. Unidirectional
Picks up sound predominantly from one direction. This includes cardioid and hypercardioid
microphones (see below).

Cardioid

Cardioid means "heart-shaped", which is the type of pick-up pattern these mics
use. Sound is picked up mostly from the front, but to a lesser extent the sides as
well.

Uses: Emphasizing sound from the direction the mic is pointed whilst leaving
 some latitude for mic movement and ambient noise.

Notes:
• The cardioid is a very versatile microphone, ideal for general use. Handheld mics are usually
cardioid.
• There are many variations of the cardioid pattern (such as the hyper cardioid below).

Hypercardioid

This is exaggerated version of the cardioid pattern. It is very directional and

eliminates most sound from the sides and rear. Due to the long thin design of
hyper cardioids, they are often referred to as shotgun microphones.

Uses: Isolating the sound from a subject or direction when there is a lot of
ambient noise; Picking up sound from a subject at a distance.

Notes:
• By removing all the ambient noise, unidirectional sound can sometimes be a little unnatural. It
may help to add a discreet audio bed from another mic (i.e. constant background noise at a low
level).
• You need to be careful to keep the sound consistent. If the mic doesn't stay pointed at the subject
you will lose the audio.
• Shotguns can have an area of increased sensitivity directly to the rear.

3. Bidirectional
Picks up sound from two opposite directions.

Uses a figure-of-eight pattern and picks up sound equally from two opposite
directions.

Uses: As you can imagine, there aren't a lot of situations which require this polar
pattern. One possibility would be an interview with two people facing each other
(with the mic between them).

Loud speaker
Loud speaker is a transducer which converts electrical signal into sound signal. There are two types
of dynamic speaker: electro dynamic and permanent magnet speaker
Parts of loud speaker

• Cone: The cone is connected to the voice coil and moves air to create sound waves. Most
modern tweeters move air with a dome rather than a cone.
• Voice coil: The electromagnet that drives the cone and is alternately charged positively and
negatively
• Magnet: The non-changing magnetic field that allows the voice coil’s alternating magnetic
force to be attracted or repelled.
• Top plate, back plate and pole piece: The magnetically conductive parts that efficiently
concentrate the magnet’s energy around the voice coil.
• Spider: A springy cloth disc that keeps the voice coil and bottom of the cone from moving
off to the side and focuses the coils motion in a forward and backward motion.
• Surround: A flexible ring that keeps the cone from moving side to side while allowing it to
push forward and backwards. Together with the spider, a suspension system is formed for
the parts that move, the moving parts being the cone and voice coil.
• Flex wires and wire terminals: These components move the electrical current from the
amplifier to the voice coil.
• Dust cap: Covers the middle section of the cone and keeps debris from getting into the gap
between the magnet and the pole piece where the voice coil resides.
• Frame (or basket): Holds the entire speaker assembly together and attaches it to the cabinet

DYNAMIC LOUDSPEAKERS

There are two varieties of dynamic loudspeakers : Electro-

dynamic and permanent magnet (PM) speakers. Both work in
exactly the same way, the difference is in their construction.

The electro-dynamic speaker has a soft iron magnetic circuit,

non-retentive of magnetism, around whose centre leg, a large,
multilayer field coil is wound, as shown in Fig. When dc flows
through this field coil, it magnetizes the iron core. A magnetic
flux field directly proportional to the strength of the current
through the coil is thus set up across the air-gap. The iron core is
not permanently magnetized, it stays magnetizedonly as long as current flows through the field coil.

Improvements in permanent magnet materials have made the electro-dynamic speaker practically
obsolete, but some still exist in vintage radios. Note that these use the field coil as part of a choke
filter in the power supply, a good example of killing two birds with one stone. The electro-dynamic
speaker has disappeared completely, so far as hi-fi is concerned, the permanent magnet speaker
reigns supreme.

Permanent magnet Dynamic loud speaker

The most popular type of loudspeaker today is the
permanent magnet dynamic type. Because of its
comparative simplicity of construction and design,
the precision that may be built into it, the ease
with which it is interfaced with other equipment,
its easy adaptability to many different
applications, and its comparative freedom from
electrical trouble, the dynamic loudspeaker has
found acceptance in all kinds of reproducing systems. It is found in the smallest pocket radios and is a
major component of the most elaborate theatre systems.

The PM speaker contains a very light coil of wire affixed to the diaphragm and located
concentrically around, within, or in front of the centre of the permanent magnet. The coil (voice
coil) is free to move in the field of the magnet. Electrical impulses, varying at an audio rate, are
applied to the voice coil by the amplifier. Because these impulses are constantly changing in
amplitude and direction, a changing magnetic field is set up in the voice coil. This field reacts
with the constant field of the permanent magnet. The result is that the voice coil moves further
into the gap when the fields are opposite and attract, and farther out of the gap when they are alike
and repel. This causes an in-and-out movement of the diaphragm; consequently, we obtain sound
waves from electrical impulses. The speed at which the coil and diaphragm vibrate depends upon
the frequency of the impulses. The distance that the diaphragm moves in and out depends on their
amplitude.
Woofers
Woofer is the term commonly used for a
loudspeaker driver designed to produce low
frequency sounds, typically from around 40
hertz up to about a kilohertz or higher. There
are two types of low frequency speaker, the
commonly known woofer, and the more recent
addition the subwoofer. The latter is used for
the reproduction of frequencies below those
produced by the woofer and it is generally purchased as an add-on to an existing system.

The low frequencies speaker provides the bass of any hi-fi system. Its sole purpose is to
reduce the low frequency notes of the program source. The prime requisite for low frequency
reproduction is a large diaphragm the larger the better. In addition to large size, the diaphragm must
be of fairly heavy construction Light diaphragms just can't hold up under the vibrations encountered
under the lower audio ranges.

A woofer must be able to vibrate back and forth very easily i.e have high compliance. One
way to accomplish this is to have the diaphragm loosely connected to the frame. The gasketing that
holds the periphery of diaphragm to the frame basket is fastened so that it barely keeps the
diaphragm from slipping loose.
Rather than the loose suspension system, the cone is supported by a very flexible material so that it
can be moved very easily by the voice coil. The suspension is tight hut the sine wave at the diaphragm edge
is made very flexible.

The large speakers have more extended lows, the smaller ones more extended highs.

A woofer must also have a large voice coil to handle considerable heat. The larger the voice coil, the more
the current produced by the amplifier output circuit and, therefore, the more the power the woofer can
handle. Finally, a strong magnet can be of great help to move the heavy voice coil and cone assembly too
well. The better the woofer, the heavier the magnet assembly (unless it's ceramic).

Tweeters

A tweeter is a loudspeaker designed to produce high audio frequencies, typically from

around 2,000 Hz to 20,000 Hz. Nearly all tweeters are electro-dynamic drivers, using a voice coil
suspended within a fixed magnetic field.
There are two main types of high frequency speakers; the well-known tweeter and the more recent
super tweeter. Super tweeters can be add-ons or they can be integral with the system. Six basic
high-frequency speakers (tweeters) exist.

(i) The cone is a physically disincentive version of the woofer.

(ii) The dome, so called because of its dome-shaped diaphragm.
(iii) The horn, so named because it is a horn.
(iv) The Heil air-motion transformer which uses the principle of lever in its operation, named after
its inventor, Dr. Oskar Heil.
(v) High polymer molecular-film tweeter, uses the piezoelectric effect for its principle of operation
(used exclusively by Pioneer).
(vi) The electrostatic tweeter works on the principle of attraction or repulsion between two metal
plates.

Types of tweeters
Cone tweeter

Cone tweeters have the same basic design and form as a

woofer with optimizations to operate at higher frequencies.
The optimizations usually are:

• a very small and light cone so it can move rapidly;

• cone materials chosen for stiffness (e.g., ceramic
cones in one manufacturer's line), or good damping
properties (e.g., silk or coated fabric) or both;
• the suspension (or spider) is stiffer than for other drivers less flexibility is needed for high
frequency reproduction;
• small voice coils (3/4 inch is typical) and light (thin) wire, which also helps the tweeter cone
move rapidly.

Cone tweeters are relatively cheap, but do not have the dispersion characteristics of domes. Thus
they are routinely seen in low cost applications such as factory car speakers, shelf stereo systems,
and boom boxes. Cone tweeters can also be found in older stereo hi-fi system speakers designed and
manufactured before the advent of the dome tweeter. They are now a rare sight in modern hi-fi
usage.
Dome tweeters

A dome tweeter is
constructed by attaching a voice
coil to a dome, which is attached to
the magnet or the top plate via a
low compliance suspension. These
tweeters typically do not have a
frame or basket, but a simple front
plate attached to the magnet
assembly. Dome tweeters are
categorized by their voice coil diameter. The majority of dome tweeters presently used in hi-fi
speakers are 25 mm (1 in) in diameter. A variation is the ring radiator in which the 'suspension' of
the cone or dome becomes the major radiating element. These tweeters have different directivity
characteristics when compared to standard dome tweeters.

Horn tweeters

A horn is a tube so flared (tapered) that the

diameter increases from a small value at one end
called the throat to a large value at the other end
called the mouth. Horns, have been used for
centuries for increasing the radiation of the human
voice and musical instruments. Horn couples the
small voice coil area to a large area of air. In this
way, the horn acts as an acoustic transformer and
converts the relatively high impedance at the throat
and driver.

CRYSTAL LOUDSPEAKERS

Rochelle-salt crystals have the property of becoming physically distorted when a voltage is applied
across two of their surfaces. This property is the basis of the crystal type of speaker driver,
illustrated in Fig. The crystal is clamped between two electrodes across which the audio frequency
 output voltage is applied. The
crystal is also mechanically
connected to a diaphragm. The
deformations of the crystal caused
by the audio frequency signal
across the electrodes cause the
diaphragm to vibrate and thus to
produce sound output. Crystal
speakers have been impractical for
reproduction of the full audio-frequency range because the input impedance is almost completely
capacitive. Thus it is difficult to couple power into them. At high audio frequencies, the reactance
becomes lower (Xc = 1/2f C) and the relative amount of power smaller. In the bass range, stresses
on the crystals are very great, and crystals have been known to crack under stresses. Consequently,
crystal units have found some use in tweeters (the high-frequency portion of dual speaker units) and
rarely even in this application because their response is not linear.

Electrostatic (Condenser/Capacitor) speaker

A detailed view of a modern electrostatic
speaker is shown in Fig. The practical speaker
of today uses push-pull, with a built-in step-up
transformer to work from the ordinary 8 ohm
amplifier output tap. The polarizing voltage is
applied to the centre or movable plate through
a resistor that keeps the voltage stable during
variations in the signal voltage. The signal
voltage is applied to the two outside plates.
Because the diaphragm is centered between
the two plates that attract it equally, there is
no bending when there is no signal. Also, because of the push pull action the diaphragm can move
twice as far in response to signal voltages for the same amount of compression of the dielectric
material.
The major weakness of the electrostatic speaker requires the dc bias is that it to be much larger
than the applied audio signal. In practical speakers, 1,000 to 1,200 volts may be used. Further,
when we get into the bass frequency ranges, a great deal of power would be required to get enough
output. To produce such power, the speaker area would have to be very large. So, even though full
range electrostatic speakers have been constructed, in practical use electrostatic speakers have been
mostly confined to frequencies above 1,000 Hz.

The step-up transformer and the high voltage polarizing supply is usually built right into the modern
electrostatic. Often the electrostatic unit and its matching woofer are sold together as a complete
system. Some high class systems use electrostatics to reproduce the high frequencies. Koss uses
electrostatics on some of their stereo headphones

AM Receiver

Super heterodyne is basically a process of designing and constructing wireless communications

such as radio receivers by mixing two frequencies together in order to produce a difference
frequency component called as intermediate frequency (IF), so as to reduce signal frequency prior
to processing.
A super heterodyne receiver usually consists of an antenna, RF amplifier, mixer, local oscillator, IF
amplifier, detector, AF amplifier and a speaker.
The working of a super heterodyne receiver is explained with the help of the block diagram given
below in Fig1 along with the waveforms at the output of each block.

• The super heterodyne receiver, the incoming signal through the antenna is filtered to reject
the image frequency and then amplified by the RF amplifier.
• RF amplifier can be tuned to select and amplify a particular carrier frequency within the AM
broadcast range. Only the selected frequency and it two sidebands are allowed to pass
through the amplifier.
• The carrier of the received signal is called radio frequency carrier and its frequency is radio
frequency fRF and the local oscillator signal operates at fOSC. The amplified RF frequency is
then mixed with the local oscillator frequency.
• The combining of these two signals is done at the mixer which produces sum and difference
frequency signals of the incoming carrier signal and local oscillator signal,
• The sum frequency is rejected by the filter and the remaining difference frequency signal
which is a down converted frequency signal is called as intermediate frequency (IF) carrier

• The frequency of local oscillator is not same as the frequency to which RF amplifier is
tuned. Local oscillator is tuned to a frequency that may be either higher or lower than the
incoming frequency by an amount equal to the IF frequency.
• Thus idea of the super heterodyne receiver is to reduce the high frequency radio components
of the incoming carrier to a fairly low, fixed value such as to be processed at the different
stages of the receiver, and also to provide good stability, gain and proper selectivity and
fidelity.
• The modulation of the IF carrier signal is same as that of the original carrier signal and it has
a fixed frequency of 455kHz which is amplified by one or more stages of amplification.
• The IF signal is amplified with the help of IF amplifier which raises its level for the
information extraction process. Also the IF amplifier fulfills most of the gain and bandwidth
requirements of the receiver.
• IF amplifier operations are independent to the frequency at which receiver is tuned,
maintaining the selectivity and sensitivity of the super heterodyne receiver considerably
constant throughout the tuning range of the receiver.
• This amplified IF signal is applied to the detector to detect the information signal component
from 455 kHz IF, to reproduce the original information data, which is generally in the form
of audio signal.
• The detector stage eliminates one of the sidebands which is still present and separates the RF
from the audio components of the other sideband.
• The RF component is filtered out and audio is supplied to the audio stages for amplification.
• The generated audio signal is then applied to the AF amplifier to increase the audio
frequency level of the signal and to provide enough gain to drive the speaker or headphones.
• A speaker is connected to the AF amplifier to play the audio information signal.
• An important part of superheterodyne receiver is Automatic gain control (AGC) which is
given to the RF, IF and mixer stages in order to generate constant output irrespective of the
varying input signal.
• Superheterodyne radio receiver in spite of being more complicated than some of the other
receivers offers many advantages in terms of performance, most importantly the selectivity.
It is more efficiently able to remove unwanted and distorting signals than other forms like
TRF and regenerative receivers.
 • Due to the enormous advantages provided by the super heterodyne receivers compared to
the other radio receivers, they are widely used in all broadcast radio receivers, commercial
radios as well as televisions operate on the basis of the super heterodyne principle.

FM Receiver

The block diagram of an FM receiver is shown in figure. The RF amplifier amplifies the received
signal intercepted by the antenna. The amplified signal is then applied to the mixer stage. The
second input of the mixer comes from the local oscillator. The two input frequencies of the mixer
generate an IF signal of 10.7 MHz. this signal is then amplified by the IF amplifier.

The output of the IF amplifier is applied to the limiter circuit. The limiter removes the noise in the
received signal and gives a constant amplitude signal. This circuit is required when a phase
discriminator is used to demodulate an FM signal.

The output of the limiter is now applied to the FM discriminator, which recovers the modulation
signal. However, this signal is still no the original modulating signal. Before applying it to the audio
amplifier stages, it is de-emphasized. De-emphasizing attenuates the higher frequencies to bring
them back to their original amplitudes as these are boosted or emphasized before transmission. The
output of the de-emphasized stage is the audio signal, which is then applied to the audio stages and
finally to the speaker. It should be noted that a limiter circuit is required with the FM discriminators.
If the demodulator stage uses a ratio detector instead of the discriminator, then a limiter is not
required. This is because the ratio detector limits the amplitude of the received signal. In figure a
dotted block that covers the limiter and the discriminator is marked as the ratio detector.

In FM receivers, generally, AGC is not required b because the amplitude of the carrier is kept
constant by the limiter circuit. Therefore, the input to the audio stages controls amplitudes and there
are no erratic changes the volume level. However, AGC may be provided using an AGC detector.
This generates a DC voltage to control the gains of the RF and IF amplifier.
A stereo FM receiver has three major sections

Mono mode, stereophonic mode, section common to both mono and stereo modes

The section that is common to both mono and stereo modes is a standard FM receiver that recovers
the modulating signal. The output section is routed to the remaining two sections. The output
consists of both the left and right channel marked as (L+R) in fig. this output is applied to the mono
section and the speaker produce audio signals monophonic mode.

The stereo section is more complicated. It uses three filters to extract(L+R) and (L-R) signals and
the pilot carrier from the discriminator output. The (L+R) signal is obtained from the low pass filter,
which contains frequencies between 50hz and 15 KHz. This signal delayed for a fixed time before
applying it to the matrix and the de-emphasis network. This is done to simultaneously get the (L+R)
and (L-R) signals at the matrix. The matrix network separates the left(L) and right® channels.
These are then de-emphasized and amplified by the audio amplifier and are given to their respective
speakers.

A band pass filter is used to extract the (L-R) signal varying between 23-53 KHz. It is a double-side
band(DSB) signal. This signal is applied to an AM detector to demodulate. The transmitter uses a
38 KHz carrier signal to get a DSB-SC signal from the (L-R) signal. Thus , at the receiver a carrier
of 38 KHz is required to demodulate the received (L-R) signal.

The pilot carrier of 19 KHz is extracted using another band pass filter, this pilot carrier is given to
the frequency doublers, which doubles its frequency to 38 KHz. After amplification of this the AM
detector detects the(L-R) signal, which is carrier, it is applied to the AM detector matrix. As some
time is taken for the (L-R) signal to demodulate, the (L+R) signal is delayed so that both (L+R) and
(L-R) reach the matrix at the same time.

2.1 Audio System

5.1 Home Theater

5.1 Surround sound systems are one of
the widely used surround sound setup
in home theater systems. Usually-
Dolby Digital and DTS encoded in a
DVD are 5.1 channel audio
formats. 5.1 surround sound
technologies produces five channels of
sound in the left, right, center, left-
surround and right-surround positions.
These five channels are the minimum
required to produce 5.1 surround
sounds. The dot decimal (.1) represents
the channel for LFE (low frequency
effects), which is usually sent to a subwoofer. Other 5 units are capable for handling the frequency
range except low frequency(Usually they are capable of handling the frequency range from 100Hz
to 22Khz and no need for any other higher frequency component like tweeter). These five units are
usually called satellite units.
 Figure shows the structure of the decoder, with the Lt and Rt input signals being passed straight to
a combining network from which the decoded outputs are obtained. The inputs are also routed through
a band-pass filter to simple passive sum-and-difference decoders. The filtering removes low frequencies
which carry no useful directional information, and high frequencies which could be distorted by amplitude or
phase errors in the recording medium.

The left-right and centre-surround channel pairs derived from the passive decoders are analyzed
independently to detect dominant signals. Four control voltages are generated (EL, ER, EC, and ES)
corresponding to the relative strength of the dominant signal in the left, right, centre and surround channels.
If a certain threshold is exceeded, they are used to adjust the gain of eight VCAs — four working on the level
of the Lt signal and four affecting the Rt signal. This octet of gain-adjusted signals is then inverted and
combined with the original Lt and Rt signals to produce the four 'directionally enhanced' output signals — L,
C, R, and S.

Display system
CRT (Cathode Ray Tube)
The picture tube shown in Fig is very similar to the cathode-ray tube used in an oscilloscope. The
glass envelope contains an electron gun structure that produces a beam of electrons aimed at the
fluorescent screen. When the electron beam strikes the screen, light is emitted. The beam is
deflected by a pair of deflecting coils mounted on the neck of the picture tube in the same way and
rate as the beam scans the target in the camera tube. The amplitudes of the currents in the horizontal
and vertical deflecting coils are so adjusted that the entire screen, called raster, gets illuminated
because of the fast rate of scanning.

The video signal is fed to

the grid or cathode of the
picture tube. When the
varying signal voltage
makes the control grid less
negative, the beam current
is increased, making the
spot of light on the screen
brighter. More negative grid
voltage reduces the brightness. if the grid voltages is negative enough to cut-off the electron beam
current at the picture tube there will be no light. This state corresponds to black. Thus the video
signal illuminates the fluorescent screen from white to black through various shades of grey
depending on its amplitude at any instant. This corresponds to the brightness changes encountered
by the electron beam of the camera tube while scanning the picture details element by element. The
rate at which the spot of light moves is so fast that the eye is unable to follow it and so a complete
picture is seen because of the storage capability of the human eye.

Colour picture tube

The colour television camera separates the primary hues from the televised scene and the colour
picture tube recombines them. The colour picture tube consists of three electron guns(red, blue and
green gun) in one picture tube envelope. The three guns are placed in the neck of the tube in a
triangle(delta). The
combinations of these
primary colours produce
all the other colours,
including white.
The phosphor on
the screen or face plate
is considerably different
from the phosphor of monochrome picture tubes. Instead of a solid coating of one phosphor on the
screen, each of three phosphors is placed in dots along a horizontal axis in a triangle fashion. The
colour tube called the trigun tricolor tube also has a shadow mask. It ensures that the beams from
the three electron guns hit their respective phosphor dots.
The colour tube is scanned in the same
way as a black and white picture tube.
If the picture being received is a black
and white picture all the three guns
will be operating. If however, the
picture being televised is in colour, the
red gun will operate for red objects,
green for green objects in the picture
and so on. If some other colour is
required, then the proper guns will
operate to mix the basic colours and produce the desired colour. The quantity of electrons hitting the
phosphor dots is controlled by their respective control grids so as to produce any desired colour.
LCD(liquid Crystal Display)
A Liquid crystal display is a passive device, which means it doesn’t produce any light to display
characters, images, video and animations. But it simply alters the light travelling through it. The internal
construction of LCD describes how the light altered when it passes through it in order to produce any
characters, images, etc
Consider a single pixel area in LCD, in which there are two polarization filters oriented at 90 degree
angle to each other as shown in figure 1.1. These filters are used to polarize the unpolarized light. The first
filter (Vertical polarized filter in figure 1.1) polarizes the light with one polarization plane (Vertical). When
the vertically polarized light passes through the second filter (Horizontal polarized filter) no light output will
produce.

Figure 1.1 Orientation of two polarization filters in LCD

The vertically polarized light should rotate 90 degrees in order to pass through the horizontal
polarized light. This can be achieving by embedding liquid crystal layer between two polarization filters. The
liquid crystal layer consists of rod shaped tiny molecules and ordering of these molecules creates directional
orientation property. These molecules in the liquid crystal are twisted 90 degrees as shown in the figure 1.2.
The vertically polarized light passes through rotation of the molecules and twisted to 90 degrees. When the
orientation of light matches with the outer polarization filter light will pass it and brightens the screen.
If the Liquid crystal molecules are twisted 90 degrees more precisely, then more light will
pass through it. Two glass transparent electrodes are aligned front and back of the liquid crystal in
order to change the orientation of the crystal molecules by applying voltage between them as shown
in figure 1.3 and figure 1.4. If there is no voltage applied between the electrodes, the orientation of
Figure 1.3
molecules will remain twist at 90 degrees and the light passes through the outer polarization filter
thus pixel appears as complete white. If the voltage is applied large enough the molecules in the
liquid crystal layer changes its orientation (untwist) so that light orientation also changes and then
blocked by the outer polarization filter thus the pixel appears black. In this way, black and white
images or characters are produced. By arranging small pixels together as a matrix will produce on
which it is possible to show different sizes of images and characters. By controlling the voltage
applied between liquid crystal layers in each pixel, light can be allowed to pass through outer
polarization filter in various amounts, so that it can possible to produce different gray levels on the
LCD screen.
Generally the electrodes is made up of Indium Tin Oxide (ITO) which is transparent material, hence
it is simply called glass electrodes plates. LCD display is also “twisted nematic LCD” because of
twist and untwist of molecules in liquid crystal layer.
In order to produce color images a color filter is placed in front of the outer polarization plate as
shown in figure1.5. The red, green and blue are the three standard colors filters are placed for every
three pixels to produce different color images by varying the intensity of each color.

Advantages
• LCD’s consumes less amount of power compared to CRT and LED
• LCD’s are consist of some microwatts for display in comparison to some mill watts for
LED’s
• LCDs are of low cost
• Provides excellent contrast
• LCD’s are thinner and lighter when compared to cathode-ray tube and LED

Disadvantages of an LCD’s
• Require additional light sources
• Range of temperature is limited for operation
• Low reliability
• Speed is very low
• LCD’s need an AC drive

Applications of Liquid Crystal Display

Liquid crystal technology has major applications in the field of science and engineering as well
on electronic devices.
• Liquid crystal thermometer
• Optical imaging
• The liquid crystal display technology is also applicable in the visualization of the radio
frequency waves in the waveguide
• Used in the medical applications

LED TV

LED (Light Emitting Diodes) TVs are basically LCDs only. The difference is that the lamp behind
the screen that was used to illuminate the fluorescent display in LCD is replaced by small LEDs.
The working of the TV remains the same, but due to the use of LEDs the screen is much slimmer in
size, power efficient and can yield a true black effect to a much greater extent.
Graphics Display

• Interactive raster-graphics systems typically employ several processing units.

• In addition to the CPU, a special purpose processor called the video controller or display
controller is used to control the operation of the display device.
• Here the frame buffer is in the system memory, the video controller access the frame buffer
to refresh the screen.

Video Controller
• A fixed area of the system memory is reserved for the frame buffer, and the video controller
is given direct access to the frame buffer memory.
• The co-ordinates of the graphics monitor starts at the lower left screen corner. Positive x
values increasing to the right and y values iincreasing from bottom to top.

Display Processor
• The purpose of the display processor or graphics controller is to free the CPU from the
graphics chores. In addition to the system memory a separate display processor memory area
can also provided.
• A major task of the display processor is digitizing a picture definition given in an application
program into a set of pixel-intensity values for storage in the frame buffer. This digitization
process is called scan conversion.
• Lines and other geometric objects are converted into set of discrete intensity points.
Characters can be defined with rectangular grids, or they can be defined with curved
outlines.
• To reduce the memory space required to store the image information, each scan line are
stored as a set of integer pairs.
The above diagram shows the refresh operation of video controller. Two registers are used to store
the co-ordinates of the screen pixels. Initially x=0 and y=ymax. One number of each pair indicates
an intensity value, and the second number specifies number of adjacent pixels the scan line that is
also having same intensity. This technique is called run-length encoding.

• The value stored in the frame buffer corresponding to this pixel position is retrieved.
• And the x value is incremented by 1 and the corresponding y value is retrieved, like that the
pixel values are retrieved line by line.
• Once the last pixel is reached again the registers are reset to initial value to repeat the
process

At the start of a Refresh Cycle:

• X register is set to 0 and y register is set to ymax. This (x, y') address is translated into a
memory address of frame buffer where the color value for this pixel position is stored.

• The controller receives this color value (a binary no) from the frame buffer, breaks it up into
three parts and sends each element to a separate Digital-to-Analog Converter (DAC).

• These voltages, in turn, controls the intensity of 3 e-beam that are focused at the (x, y)
screen position by the horizontal and vertical drive signals.

• This process is repeated for each pixel along the top scan line, each time incrementing the X
register by Y.

• As pixels on the first scan line are generated, the X register is incremented through xmax.
• Then x register is reset to 0, and y register is decremented by 1 to access the next scan line.

• Pixel along each scan line is then processed, and the procedure is repeated for each
successive scan line units pixels on the last scan line (y=0) are generated.

• For a display system employing a color look-up table frame buffer value is not directly used
to control the CRT beam intensity.
 • It is used as an index to find the three pixel-color value from the look-up table. This lookup
operation is done for each pixel on every display cycle.

• As the time available to display or refresh a single pixel in the screen is too less, accessing
the frame buffer every time for reading each pixel intensity value would consume more time
what is allowed:

• Multiple adjacent pixel values are fetched to the frame buffer in single access and stored in
the register.

• After every allowable time gap, the one-pixel value is shifted out from the register to control
the warm intensity for that pixel.

• The procedure is repeated with the next block of pixels, and so on, thus the whole group of
pixels will be processed.

Compact DISC
In the Laser Vision System, which records audio or 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 signal. On the compact disc, the
signal is recorded in a similar manner, but the information is present in the track in digital form.
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, (figure 1 ).
The density of the information on the compact disc is very high; the smallest unit of audio
information (the audio hit) covers an area of 1 µm2 on the disc, and the diameter of the scanning
light spot is only 1 µm. The pitch of the track is 1.6 µm, the width 0.6 µm and the depth 0.12 µm.
 The minimum length of a pit or the land between
two pits is 0.9 µm; the maximum length is 3.3 µm.
The side of the transparent carrier material
T in which the pits 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 about 8 rev/s to about 3.5 revs (or 480 rpm to
about 210 rpm).
What is a DVD?
A Digital Versatile Disc/Digital Video Disc [DVD], is an optical disc storage medium like a
compact disc [CD], but with greater data storage and high quality audio and video formats. The
clarity, when comparison with a CD is almost six times higher

Specifications of DVD

• DVD has a total capacity of 4.7 GB.

• It can run a high-quality video for a maximum of 133 minutes.
• DVD has a video compression ratio of 40:1 with an MPEG-2 compression.
• Wavelength of a DVD is almost 650 nanometres laser diode light.
• DVD’s can be written at a speed of almost 18x to 20x. [1x = 1318 Kbps].

Advantages of DVD

• The picture quality is far better than a CD.

• Most DVD’s have Dolby Digital or DTS. Thus the clarity of the sound will be nearly equal to
that in a theatre.
• Though the technology of CD is gone, they were made with a compatibility with audio CD’s.
• The DVD has a special on-screen index quality which helps you to take a closer look at
important scenes of a movie which was earlier indexed by the publisher of the movie. This
method is not common.
• Unlike a CD player, the DVD player is specialised in taking you to the correct part which you
prefer to see. Thus, there will be no need of fast-forwarding.
• The format of a DVD can be changed according to the type of view you need. It can be a
standard TV size format and also a wide-screen TV format.
Block diagram of DVD player

Important parts of DVD player

Optical system
The optical system is made up of a laser, photo detector, prism, mirrors, and lenses. The laser and
photo detector are installed on a plastic housing, and the other components are placed in specific
places. Great care is taken in the positioning of each of these pieces because without proper
alignment, the system will not perform properly. Electrical connections are attached and the optical
system is then ready to be attached to the disk drive mechanism.

A Laser and Lens system: to focus in on the pits and land and read them. The light from this laser
has a smaller wavelength (650nm) than the light from the laser in a CD player (780 nm), which
allows the DVD laser to focus on the smaller DVD pits
Disk drive mechanism
The optical system is attached to the motor that will drive it. This in turn is connected to the other
principle parts of the disk drive including the loading tray (if present) and the spindle motor. Other
gears and belts are attached and the entire assembly is placed in the main body.

To work properly, the DVD player must focus the laser on the track of bumps. The laser can focus
either on the semi-transparent reflective material behind the closest layer, or, in the case of a
double-layer disc, through this layer and onto the reflective material behind the inner layer. The
laser beam passes through the polycarbonate layer, bounces off the reflective layer behind it and
hits an opto-electronic device, which detects changes in light. The bumps reflect light differently
than the "lands," the flat areas of the disc, and the opto-electronic sensor detects that change in
reflectivity. The electronics in the drive interpret the changes in reflectivity in order to read
the bits that make up the bytes.

Inside the DVD player, there is a good bit of computer technology involved in forming the data into
understandable data blocks, and sending them either to the DAC, in the case of audio or video data,
or directly to another component in digital format, in the case of digital video or data.

Blu-ray Disc – Definition

A Blu-ray Disc is a high density optical disc storage medium, which is used for the storage
of all high-definition digital formats like audio, video, and play-station games and so on. They have
the same physical appearance as a DVD. The name “BLU-RAY” is actually a combination of the
colour “blue” and “ray”. Here blue refers to the blue colour of the laser that is used for its reading
and ray refers to the optical ray. While trade marking a product, you are not supposed to include a
common or everyday used word. Thus the letter ‘e’ from the word “blue” was omitted.

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.

Construction and Working of Blu-Ray Disc

1. Like a DVD, the BD also has pits and bumps. The only difference is that the pits and bumps are
smaller and very closely packed. Blu-ray disc also has spiral tracks running from the centre to
the edges of the disc. The information is stored in these tracks in the form of audio and video.
These audio and video are introduced into the DVD after encoding it.
2. As told earlier a blue laser is used to focus on the DVD. The laser has a small wavelength of
precisely 405 nanometers and must be highly accurate because the pits and bumps are smaller
 and packed closely. The information stored in the Blu-Ray disc is usually very small in size.
They are only 0.15 x 10-6 meters long. Since all these are very small in size, a single-layer itself
is more than enough to hold more than 25 GB of data. Thus if a double layer is used, they can
easily hold information up to 5o GB.
3. The Blu-Ray disc does not have these issues because the data is stored on top of a poly-
carbonate layer which is about 1 millimeter thick. This stops the problem of birefringence and
causes no distortion to the reading of data. This also has an advantage in regard to the closeness
of the data to the objective lens. Due to this closeness to the surface, the BD has a outside hard
cover to prevent scratching and finger prints.
Types of Blu-Ray Disc
Similar to a DVD, BD also has different versions according to its application. The common types are
1. Read only memory Blu-Ray disc [BD-Rom] – This type of BD can only be read but cannot be
written over. The content will be pre-recorded.
2. Recordable Blu-Ray disc [BD-R] – This BD is mainly used for storage of PC data.
3. Re-writable Blu-Ray disc [BD-RW] – This BD is mainly used for storage of PC data. The contents
in this disc can be written over and over.
4. Re-writable Blu-Ray disc [BD-RE] – This BD is mainly used for recording of data to be used in
HDTV. This disc can also be written over again and again.

Blu-Ray Disc (BD) vs DVD

• Both of them have the same physical appearence. [Thickness = 1.2 mm]

• The single layer Blu-ray disc can store up to 27 GB data. A singe layer DVD can hold only 4.7
Gb of data. Thus a BD can hold almost 13 hours of normal video and 2 hours of high-definition
video. A double layer BD gas a storage capacity of 50 GB which can play almost 20 hours of
normal video and 5 hours of HD.
• A DVD needs two substrates and they should be bonded. But a Blu-ray disc requires only one
substrate.
• The production cost of Blu-ray is lesser than that of a DVD because there is no need for
bonding of substrates. Thus the production materials are lessened. This causes a lesser
production time than that for a DVD.
• The Blu-Ray disc uses violet-blu laser with improved lens specifications, while a DVD uses red
laser. This causes the focus to increase, thus helping in the recording of both small and high
density pits on the BD.
• The wavelength used for BD is 400 nanometers. DVD has a wavelength of 650 nanometers.
This decrease in wave lenth helps in high density medium storage.
• The layer in a blu-Ray disc is very close to the laser lens on its player. Thus the precision of the
data displayed will be higher with less distortion than a DVD.

Storing of data
 In the recording process an input stream of digital information is converted with an encoder
and modulator into a drive signal for a laser source. The laser source emits an intense light beam
that is directed and focused into the storage medium with illumination optics. As the medium moves
under the scanning spot, energy from the intense scan spot is absorbed, and a small localized region
heats up. The storage medium, under the influence of the heat, changes its reflective properties.
Since the light beam is modulated in correspondence to the input data stream, a circular track of
data marks is formed as the medium rotates. After every revolution, the path of the scan spot is
changed slightly in radius to allow another track to be written.

Readout from the Disc

In the optical keep pick-up unit, the laser diode emits laser beam from a small point into an elliptical
or conical distribution. This beam is passed through various prism and lens to form a very small
diameter light beam on the disc surface at the centre of the track.

The objective lens is controlled by the tracking and focusing coil to keep the beam focused on the
CD and keep the condensed beam at the centre of the track. This laser beam is reflected back by the
flat area and the pits on the disc surface.

This reflected beam is applied to a group of photo diodes through objective lens, collimator lens and
some prism arrangement. This photo diode induce voltage according to the reflected beam falling
on it. Focus error and tracking error voltage generated by this photo diode array is applied to the
tracking and focusing coil to control the objective lens and data signal generated by this photo diode
array is sent to an amplifier to amplify the data signals picked up from the disc. Finally the output
from the amplifier is processed to produce the audio/video signal stored on the disc surface.
Digital Camera

The digital camera can be considered as an alteration of the conventional analog camera.
Most of the associated components are also the same, except that instead of light falling on a
photosensitive film like an analog camera, image sensors are used in digital cameras. Though
analog cameras are mostly dependent on mechanical and chemical processes, digital cameras are
dependent on digital processes. This is a major shift from its predecessor as the concept of saving
and sharing audio as well as video contents have been simplified to earth.

As told earlier, the basic components are all the same for both analog and digital cameras. But, the
only difference is that the images received in an analog camera will be printed on a photographic
paper. If you need to send these photos by mail, you will have to digitally convert them. So, the
photo has to be digitally scanned.

This difficulty is not seen in digital photos. The photos from a digital camera are already in the
digital format which the computer can easily recognize (0 and 1). The 0’s and 1’s in a digital
camera are kept as strings of tiny dots called pixels.

The image sensors used in an digital can be either a Charge Coupled Device (CCD) or a
Complimentary Metal Oxide Semi-conductor (CMOS). The image sensor is basically a micro-chip
with a width of about 10mm. The chip consists arrays of sensors, which can convert the light into
electrical charges. Though both CMOS and CCD are very common, CMOS chips are known to be
more cheaper. But for higher pixel range and costly cameras mostly CCD technology is used.

A digital camera has lens/lenses which are used to focus the light that is to be projected and
created. This light is made to focus on an image sensor which converts the light signals into electric
signals. The light hits the image sensor as soon as the photographer hits the shutter button. As soon
as the shutter opens the pixels are illuminated by the light in different intensities. Thus an electric
signal is generated. This electric signal is then further broke down to digital data and stored in a
computer.
Color Filtering using Demosaicing Algorithms

The sensors used in digital cameras are actually coloured blind. All it knows is to keep a track of the
intensity of light hitting on it. To get the colour image, the photosites use filters so as to obtain the
three primary colours. Once these colours are combined the required spectrum is obtained. The
main advantage of this method is that only one sensor is required for the recording of all the colour
information. Thus the size of the camera as well as its price can be lessened to a great extent.

Pixel Resolution of a Digital Camera

The clarity of the photos taken from a digital camera depends on the resolution of the camera. This
resolution is always measured in the pixels. If the numbers of pixels are more, the resolution
increases, thereby increasing the picture quality. There are many type of resolutions available for
cameras. They differ mainly in the price.

Parameters of a Digital Camera

Like a film camera, a digital camera also has certain parameters. These parameters decide the clarity
of the image. First of all the amount of light that enters through the lens and hits the sensor has to be
controlled. For this, the parameters are
1. Aperture – Aperture refers to the diameter of the opening in the camera. This can be set in
automatic as well as the manual mode. Professionals prefer manual mode, as they can bring their
own touch to the image.
2. Shutter Speed – Shutter speed refers to the rate and amount of light that passes through the
aperture. This can be automatic only. Both the aperture and the shutter speed play important roles in
making a good image.
3. Focal Length – The focal length is a factor that is designed by the manufacturer. It is the
distance between the lens and the sensor. It also depends on the size of the sensor. If the size of the
sensor is small, the focal length will also be reduced by a proportional amount.Lens – There are
mainly four types of lenses used for a digital camera. They differ according to the cost of the
camera, and also focal length adjustment. They are

1. Fixed-focus, fixed-zoom lens – They are very common and are used in inexpensive
cameras.
2. Optical-zoom lenses with automatic focus – These are lenses with focal length
adjustments. They also have the “wide” and “telephoto” options.
3. Digital zoom – Full-sized images are produced by taking pixels from the centre of the image
sensor. This method also depends on the resolution as well as the sensor used in the camera.
4. Replaceable lens systems – Some digital cameras replace their lenses with 35mm camera
lenses so as to obtain better images.
In a CCD sensor, every pixel's charge is transferred through a very limited number of output nodes
to be converted to voltage, buffered, and sent off chip as an analog signal. In a CMOS sensor, each
pixel has its own charge-to-voltage conversion, and the sensor often also includes amplifiers, noise
correction, and digitization circuits, so that chip outputs are digital bits
Camcorder
The word camcorder comes from combining the two words, camera and recorder. How
a camcorder works is by recording audio and video and then saving those to a storage device,
there by creating your own movies/videos and capturing life on video.

One of the most popular camcorders today is the DVD type, which can replay video on a home
DVD player via the digital camcorders recording and hence burning directly to DVD.

The convenience of recording directly to the high-resolution DVD format is incomparable.

Also, instant access to any scene eliminates the time and hassle of fast-forwarding and
rewinding, as with tape formats. These camcorders work by allowing the DVD format to save
memories securely in high-resolution. Also it is important to note that the DVD type
camcorders LCD displays a list of the recorded scenes for quick, easy searching.

DVD camcorders provide superb recording quality by digitally recording to a DVD disc and not
on tape. Another benefit of recording with a DVD camcorder is its flexibility. You can use your
camera to record at home, use it as a storage medium, or in the office connected to your PC.
Images recorded onto DVD-RAM or DVD-R discs can also be played on a DVD recorder or
DVD player, so you don't have to hook the camcorder up to a TV to watch your recordings.

Advantages of LED TV
1. Consumes less power compared to LCD, plasma and CRT
2. Thinner and lighter compared to CRT and LCD
3. Contrast is better than LCD
4. It has very good brightness
Disadvantages of LED TV
1. Need additional light source
2. Limited range of temperature for operation
3. Narrow viewing angle
4. Little motion blur