winter 12 examinations - wordpress.com · 2015-05-25 · 2nd chroma amplifier: the second chroma...

MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION (Autonomous)

(ISO/IEC - 27001 - 2005 Certified)

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WINTER – 12 EXAMINATIONS

Subject Code: 12190 Model Answer Page No: ____/

Q.1 a) Attempt any THREE of the following: 12 marks

i. State need of graphic equalizer in audio amplifier. Draw its circuit diagram.

(Need of graphic equalizer- 2 marks (any 3 points), diagram (any one)- 2 marks)

In sound recording system the low power frequency notes should be emphasized

before recording, so that these notes are carried to much higher power level,

compared to noise signal. This will improve signal to noise ratio of the recording

system.

At the receiving end or the playback end, these should be a facility to bring the

boosted signal back to their original levels. This is similar to pre-emphasis and de-

emphasis process.

The recovery of the original sound signal from the playback circuit by conversion

process of de-emphasis at the receiver is called equalization.

In this type of tone control the audio spectrum is divided in to narrow band. Each

band has an individual slider which can boost or cut the signals in that band from

+15 to -15dB. The center frequency of each band is generally based on an octave.

So to get boost or cut in frequency to get the proper effect like classical, jazz, rock

or pop as well as treble and bass effect we need the graphic equalizer.

OR



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ii. State the principle of detection used in CD player with diagram.

(Diagram -2 marks explanation-2 marks)

Laser Diode: A laser beam produced by solid state laser of semiconductor aluminum

gallium arsenide is made incident on the CD through a half silvered mirror.

Reflected Beam: The reflected beam is reflected from the aluminum flat surface

represents digit 1. There is only a little reflection from a pit and it represents 0. Thus

the returning laser beam is the replica of the original laser beam modulated by binary

digit of audio signal.

Optical mirror and lens system: The mirror allows beam to pass through itself but

does not allow the returning beam to pass. The lens system allows the beam to confine

on a proper track for detection purpose. Lenses used are collimated lenses, concave

lenses and objective lenses.

Photodiode Detector: The binary digit is represented when this ON-OFF reflected

light falls on a photo sensitive diode. The diode converts the light in to electrical signal

which corresponds to digital data.



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Digital audio to DAC circuit: The digital output of a diode is processed and

converted in to original analog signal by using DAC.

Control: A clock signal is obtained from the disc itself. It is compared with the crystal

oscillator signal any discrepancy results in generation of a correction signal which is

applied to a servo system.

Servo System: This system issues command such as motor speed correction, track

correction and focus correction. In case only error signal received from control block.

iii. Define “Aspect ratio”. Why width is more then height?

(Definition 2-mark and any two reasons-1 mark each)

Definition: Width to height ratio of a picture frame is called aspect ratio. Standard aspect

ratio of 4:3 is preferred for most televisions.

Width is kept longer than height because of the following facts:

In human affairs most of the motion occurs in horizontal plane so a larger width is

desirable.

The eyes can view with more ease and comfort when width of a picture is mote

than height.

The fovea ( the surface of maximum selectivity and resolution at the centre of

retina in the eye has greater width than height.

The vision due to pair of eyes is in the horizontal plane and the range of movement

of both the eye balls is more in horizontal plane as compared to vertical plane.

iv. Explain basic principle of Yagi-uda antenna.

(Principle Yagi-uda antenna- 2 mark &diagram-2 mark)

This antenna is widely used with television receiver for a location within 40 to

60km from the transmitter has folded dipole with one reflector one director.

The elements of its array are as shown in fig.(a) and is relatively unidirectional as

seen from its radiation pattern drawn in fig.(b)

Function of reflector: The reflector rod is longer in length by about 10% of the

length of dipole. The dipole is 0.5λ and reflector is 0.55λ. Reflector acts as s tuned

circuit whose resonant frequency is lower than the frequency of the signal being

received by the active dipole element.

Function of director: Director concentrates the energy in the same direction in

which the radio wave is moving. The director rod is shorter than the dipole by

about 10% of the length of dipole.



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Q.1 b) Attempt any ONE of the following: 8 marks

i) Draw block diagram of PAL-D decoder and explain it.

(Diagram-4 marks block wise explanation-4 marks)

Explanation:

Chroma signal selection: Its function is to select chroma and colour burst signal

from the incoming CCVS signal by chroma signal selection circuit. It essentially

consist of band pass circuit whose centre frequency is chosen to be equal to that of

chroma sub-carrier it self i.e.4.43MHz.

1st chroma amplifier: The chroma and burst signals are amplified by first chroma

amplifier which is controlled by DC voltage developed by the Automatic Chroma

Control (ACC) amplifier.

2nd

chroma amplifier: The second chroma amplifier incorporates colour

saturation control circuit. The output of colour killer also feeds into it.

PAL delay line (separation of U and V colour phasors): This network separated

U and V signals with are then fed to respective demodulator.

Gated burst amplifier: The gated burst amplifier separates the burst pulses and

amplifies them a level suitable to operate the burst phase discriminator.

Automatic Chroma Control (ACC): The magnitude of the voltage so fed back is

proportional to the magnitude of the burst and therefore to the amplitude of chroma

signal itself. This voltage is used to control the first stage of chroma amplifier in

such way to ensure constant chroma signal amplitude.

Burst phase discriminator: It is sensitive to burst pulses and is designed to detect

any differences which might exist between the phase of burst pulse and that of the

reference oscillator. It produces at its output a dc voltage whose magnitude and

polarity are proportional to the magnitude and direction of the detected phase

difference.

Burst phase identifier: This circuit is able to identify the phase relationship of the

colour burst.



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1800 switch: This switch is used to periodically invert the waveform fed to the v-

signal demodulator.

Colour killer control: This is just a half wave rectifier which produces a steady dc

potential from the succession of burst pulses. During black and white transmission

the dc potential is absent and hence biases the 2nd

chroma amplifier to cutoff state.

ii) Draw block diagram of monochrome T.V. receiver. Write the values of picture carrier

and sound carrier IF frequencies.

(Diagram-5 marks and values of frequencies 1.5-mark each)

Picture carrier IF frequencies: 38.9MHz

Sound carrier IF frequencies: 33.4MHz

Q.2 Attempt any FOUR of the following: 16 marks

a) Compare stereo and mono amplifier

(any four points-1 mark each)

Stereo amplifier Mono amplifier

Stereo means solid and phone is sound in greek,

means three dimensional sound.

Mono means one sound or one dimensional

sound.

Sound arises from the two different amplifiers

so that sound appears to be surrounded.

Monophonic sound system has one source



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It has two different channels (left and right)

corresponds to two amplifiers and loud

speakers.

Mono amplifier has one channel and one

speaker system.

Stereo amplifiers can have multi speaker

system which gives surround system.

Multi loud speakers can be connected but with

same source.

With stereo system sound reproduced is actual

feels original

The monophonic sound is cheap to be produced

but lacks naturalness.

Used in Hi-Fi amplifier system. Used in public address system.

b) What is negative modulation? State its advantages.

(Definition-2 marks & advantages (if only heading is written then also marks should

be given)-2 marks (any 2 points))

Definition: When the polarity of modulating video signal is so chosen that sync tip lie at

100% level of carrier amplitude and increasing brightness produces decreases in the

modulation envelope, it is called negative modulation.

Advantages of negative modulation:

Noise interference on picture signal is less: The noise pulse in the transmitted

signal shall increase the amplitude is the carrier which will move towards the

black. The noise pulses would tend to produce black spots which are less

noticeable against a grey background.

More power available from the transmitter: The transmitter may be over

modulated during the sync pulses without adverse effect since the non-linear

distortion thereby introduced does not very much affect the shape of sync pulses.



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Saving in transmission power: Carrier amplitude will remain low for most of the

time as he signal content is more in white than in black. This will cause saving in

transmission power.

c) What is colour burst? State its importance with neat sketch.

(Colour burst signal definition-2 marks & diagram 2-marks)

Colour burst signal: The transmitted signal does not contain the subcarrier frequency but

it is necessary to generate it in the receiver with correct frequency and phase relationship

for proper detection of the colour sidebands. To ensure this, a short sample of the

subcarrier oscillator, (8 to 11 cycles) called the “colour burst” is sent to the receiver

along with sync signals. Subcarrier frequency is 4.43MHz.

d) With neat sketch, explain VSB transmission.

(Diagram- 2 marks & explanation-2marks)

The low video frequencies contain the most important information of the picture

and any effort to completely suppress the LSB would result in phase distortion at

these frequencies. This distortion will be seen by the eye as “smear” in reproduced

picture.

Therefore as a compromise, only a part of the lower sideband, is suppresses, and

the radiated signal then consists of a full upper side band and a carrier signal and

vestige (remaining part) of the partially suppresses lower sideband.



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This pattern of transmission of the modulated signal is known as Vestigial

Sideband transmission.(VSB).

In 625 line system, frequencies up to 0.75MHz in the lower sideband are dully

radiated.

Because of filter design difficulties it is not possible to terminate the B.W. of a

signal abruptly at edges of the sidebands.

As shown in figure above saving of band space which results from vestigial

sideband transmission. The picture signal is seen to occupy a bandwidth of

6.75MHz instead of 11MHz.

e) State working of LNBC with diagram.

(Diagram-2 marks and working -2 marks)



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Dish antenna and feed horn: A feed horn is actually a flared open waveguide

section which is mounted at focal point and its function is to receive signals

reflected towards it by the delivers these to the close by located unit called as Low

Noise Block Convertor (LNBC).

Low Noise Amplifier (LNA): The CVS collected by the feed horn is fed to LNA

which is specially designed to provide enough gain which maintains maximum

possible S/N ratio.

Mixer(down convertors): Mixer translates the incoming microwave signals to a

lower frequency range of 950-1450MHz. This is achieved by mixing local

oscillator frequency of 5150 MHz at mixer and selecting only the difference from

output.

Band pass filter: A BPF at the output mixer separates the wanted IF signals from

the other signals.

Multistage IF amplifier: It amplifies the down converted signals and then sent

through high grade coaxial cable to the CATV station.

Q.3 Attempt any FOUR of the following: 16 marks

a) Draw the composite video signal and label it. (Diagram-3 marks & label-1 mark)



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b) Write any four specification of DISH antenna (any four points-1 mark each)

Diameter: 5m/3.7GHz

Mount: Azimuth elevation type

Frequency: 3.7GHz-4.2GHz (depends on band of operation)

Gain: 42dBi/40.7dBi

Drive: Motorized & manual

Wind velocity: 100kmph

c) What is interlace scanning? What is the use of it?

(Definition with diagram-3 marks & use-1 mark)

Interlaced Scanning:



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In T.V. pictures an effective rate of 50 vertical scans per second is utilized to

reduce flicker.

Total numbers of lines are divided in to two groups called fields (even and odd).

As shown in figure above the first sequence of scanning starts from left most ends

on middle on last line.

The vertical retrace is shown by dotted line deflects the electron beam from bottom

to top shown by dotted lines which takes 1.280ms (equal to 20 scanning lines) are

blanked in retrace.

The second sequence of scanning stars from this middle point and ends finally at

the rightmost point bottom after completing 605th

line.

Use of interlaced scanning:

To reduce flicker by scanning each frame twice in the same way as progressive

scanning.

Scanning process converts variations of light in a picture in to signals varying with

time.



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d) Write design concept for cable TV network. (4-marks for all three points(even if any

names given are written then also relevant marks should be given)

Signal reception (front end convertor or outdoor equipment): The purpose of this

section is to collect T.V signals from different sources and on conversion as necessary

deliver these through coaxial cables to corresponding signal processing units loaded in the

control room.

Signal processing (head end or indoor or control room equipment): This consists of

power dividers, satellite receivers, channel modulators, signal processors, amplifiers,

VCRs, CD-player, monitors and a combining network.

Signal distribution (cable network): Cable TV distribution system is essentially a

coaxial cable network that feeds multiplexed channel signals from the combiner to

subscribers over an area that can be wide spread in big cable systems.

e) State advantages of fluorescent display system used in CD player. (any four points-1-

mark each)

In addition to ten numerals, the display can be used to show letters including

punctuation.

It gives hexadecimal encoding for display the digits 0 to F.

To remove the ambiguity letter „B‟ is small „b‟ and number „8‟ is in 7 segment

display, otherwise both would have looked same.

It can give short message giving status information in CD player like “no disc” or

“error” etc.

The fluorescent numbers and messages can be seen in the dark also.

Q.4 a) Attempt any TWO of the following: 8 marks

i) Explain working principle of multiplexer used in cable TV with diagram.

(Diagram-2 mark & working principle-2 marks)



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The combining of several modulator and signal processor outputs is essentially

multiplexing of two or more signals for simultaneous transmission over a single

communication channel.

This is illustrated in figure above where the multiplexer is a linear mixer and all

the signals are simple added together algebraically. The resultant output signals

are composite of all the channel carries and their modulation products.

While resistive summing network and dynamic combiners using op-amp are

possible for cable system having large number of channels a transformer

coupled network is considered more suitable.

ii) Explain functions of remote control receiver used in CD player with neat diagram.

(any four functions of control-1/2 mark each (any of top load or front load player

should be considered & 2-marks for diagram.)



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Pause LED: This LED lights when the pause key on the player is presses and

the play of the CD is temporarily suspended.

Repeat LED: This LED lights when the repeat key is presses and the player

repeats playing of current track or the CD in the player.

Error LED: This LED flashes to indicate a CD operating or programming

error.

ON/OFF: This switch is used to turn the CD player ON, this also makes the

LED on the player to turn ON. Once the player use is over one can switch OFF

the unit by pressing this key once again.

PLAY/NEXT: After this switch is presses the disc in the player will start to

play from the 1st track to the last track in sequential order. NEXT button is used

to stop current track and play next track.

Pause: This button is used to stop the play of the CD player for a small period.

STOP/CM: This STOP/CM (clear memory) button can be used to stop the

track being played and clears the memory of CD player.

Repeat: If this button is pressed before the end of play, the complete play of

the disc is repeated by the player.

Rev/Fwd: The Reverse and forward buttons can be used to move forward or

backward within a particular track.

Push to open: This key is used to open disc carrying compartment of CD

player.

Select: The select button can be used to directly start playing a particular track

from the disc.

Store: The store button can be used with the select button to program the order

in which you want the tracks on the disc to be played.

Cancel: This button can be used with the select button to cancel or remove any

program stored in the memory.

iii) List the controls available on Hi-Fi amplifier. Also explain function of Mic in and Aux in.

(Listing only of controls-3 marks and function of Mic in and Aux in-1 mark)

Balance control

Loudness control

Bass and treble control

Master gain control

Blend control



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Functions of Mic. in and Aux in: These are the two inputs given to Hi-Fi amplifier

system for connecting microphone and multiple microphones from single amplifier.

Controls of all microphones are provided by Hi-Fi system.

Q.4 b) Attempt any ONE of the following: 8 marks

a) Draw block diagram of colour TV transmitter and explain function of each block.

(Block diagram-4 marks (any other relevant diagram should be considered and marks

should be given and function of each block-4 marks)

A PAL colour TV transmitter consists of following three main sections.

1. Production of Luminance (Y) and Chrominance (U and V) signals.:

Colour camera tube produces R,G and B voltages pertaining to the intensity of red,

green and blue colours respectively in pixels.

The luminance signal Y is obtained by a resistive matrix, using grass man‟s law.

Y=0.3R+0.59G+0.11B.

For colour section Y is inverted colours R and B obtained from the colour camera

tubes are added to it to get (R-Y) and (B-Y) colour difference signal.

These signals are weighted by two resistive matrix network which gives „U‟ and

„V‟ signals as U=0.493 (B-Y) & V=0.877(R-Y)

2. PAL encoder:



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PAL switch which operates electronically at 7812.5Hz with the help of bistable

multivibrator and feeds the sub-carrier to balanced modulator with phase difference

of +900 on one line and -90

0 on the next line.

The PAL encoder consists of a sub carrier generator and two balanced modulator

with filters to produce modulated sub carrier signal. These signals are added

vertically to give chroma signal (C).

Then chroma signal is mixed with Y signal along with sync. And blanking pulses

to produce Colour Composite Video Signal (CCVS).

3. Video and Audio modulators and transmitting antenna:

CCVS amplitude modulates the main video carrier. It is followed by a sharp VSB

filter to attenuate the LSB to give AMVSB signal for transmitter.

Audio signal modulates separate carrier. This modulation is FM type.

AMVSB video signal along with audio signal passes to the transmitting antenna

through Diplexer Bridge which is a whetstones bridge.

b) With neat diagram explain how EHT is generated in colour T.V.

(Diagram-4 marks and explanation-4 marks)

Explanation:

In colour TV to generate EHT up to 25KV the diode split addition technique is used. The

principle of “DIODE-SPLIT ADDITION” is illustrated in figure below.

The three layers of secondary windings are shown wound round on the ferroxide core of

the L.O.T.

Each winding is identical to the other and has the same number of turns. The same

magnitude of voltage will therefore be induced in each section every time the fly back

derived input pulse get applied to the primary winding.



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Because of the close proximity of individual layers and inter-layer capacitance exists

between each of them. It is indicated in the diagram by dotted because this capacitor

physically does not exist.

If a diode is connected between the end of one layer of winding and the start of the next

the AC voltages induced in each layer can be made to charge up all the inter-layer

capacitances to the same voltage.

Since capacitances are effectively in series, the total output voltage appearing at he output

terminal is the sum of all the voltages appearing across all of them.

The diode shown connected in series between the layers are physically embedded in the

windings and form an integral part of the transformer.

The three windings are so designed that voltage induces in each layer form the fly back

transformer is 8.33KV. This makes the total potential equal to

(8.33KV+8.33KV+8.33KV≈25KV) and forms the EHT supply source.

Q.5) Attempt any FOUR of the following: 16 marks

a) State working principle of PIL colour picture tube with diagram.

(Diagram-2 marks & working principle-2 marks)



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Working principle:

Electron beams from the three guns strikes the three phosphor stripes. The stripes of red,

green and blue phosphor glow simultaneously.

The intensity of glow being proportional to the intensity of video signal.

The eye adds the three colours emitted by the phosphor dots at a time and perceives the

resultant colour.

Due to vertical slots, electron transparency is about 50% which is more that 20% for the

delta gun picture tube. Hence its efficiency is better.

b) Compare CATV and CCTV by four points.(any four points-1 mark each(any other relevant

point should also be given marks))

Cable Television (CATV) Closed Circuit Television(CCTV)

The CATV monitor has RF, IF as well as

detector stages.

CCTV monitors does not have RF,IF and

detector stages.

Audio section is present Audio section is not present.

Pay-TV channels are present in CATV with

additional fees.

Pay-TV channels are not present.

Internet services can be provided Internet service can not be provided.

CATV service provider can broadcast live

programs from studios, some events etc. on

their local TV channels

Such facilities are not available

Various channels such as scientific, geographic,

sports news, entertainment etc. are provided by

CATV.

Such channels are not provided in CCTV.

CATV system is huge system covering not only

a small community but also large areas rather a

whole city.

CCTV can cover only small area where it is

installed for example a hospital, college etc.

Camera range of CATV is more with higher

resolution.

CCTV camera range is limited to only some

distance with less resolution.

Applications: CATV‟s are used in homes,

malls, shops for entertainment and value added

services and in corporate and business

Applications: It is used for surveillance in

college campus, industry, traffic control, crowd

control and also used for medical care and



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environment for internet services. safety.

c) What is principle of PAL-D system? Draw the diagram showing how U and V signals are

reproduced in PAL-D system. (Principle of PAL system-2 marks and diagram-2 marks)

Principle of PAL-D system:

A sub carrier signal of 4.43MHz is modulated by „U‟ and „V‟ signals. The modulation is

AMVSB type.

V-signal changes its phase by 1800 on every alternate line of the same field. It means that

if on one line V (weighted R-Y) is +900 from U (weighted B-Y), then on the next line it

would be -900 from U.

This while V and U are always perpendicular to each other. V changes its phase every

alternate line by 1800 (from +90

0 to -90

0). This is known as Phase Alteration Line (PAL)

system.

For separation of U and V signal the delay line technique is used hence the mane is Phase

Alteration by Line-Delay (PAL-D)

Diagram showing reproduction of U and V signal:



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d) With neat diagram explain the construction of vidicon camera tube.

(Diagram-2 marks and Construction-2 marks)

Construction:

The input light from scene passes through a lens system and is incident on the face plate

made of optically flat glass.

The light from the face plate falls on a target plate which has two layers. Facing face plate

is a thin coating of tin oxide which is transparent to light and is a good conductor of

electricity. This layer is called signal plate.

The back from target plate (facing the electron gun) is coated with antimony trisulphide, a

semiconductor.

The target plate is scanned by a focused electron beam produced by an electron gin

consisting of indirectly heated cathode.

A control grid (G-1)

An accelerator grid (G-2) (300V)

Focus grid(G-3) (260V)

Grid (G-4) (400V)

Deflection coils deflects the electron beam horizontally and vertically.

Focus coil sharpens beam.



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Alignment coils align the beam to the axis of the tube in the absence of deflection.

e)Write CCIRB standard for colour T.V. (any four standard- 1 mark each)

Parameters CCIR B standard

Number of scanning lines/frame 625

Field (vertical) frequency 50Hz

Line(horizontal) frequency 15625Hz

Aspect ratio(width/height) 4:3

Horizontal trace time 52µs

Horizontal retrace time 12µs

Total scanning line lost in vertical retrace 64µs

Front porch 1.5µs

Back porch 5.8µs

Horizontal sync pulse 4.7µs

Colour sub carrier frequency 4.43MHz

Colour system Phase Alteration by Line –Delay (PAL-D)

U signal(weighted B-Y) U=0.493 (B-Y)

V signal(weighted R-Y) V=0.877(R-Y)

Total vertical blanking duration 1280µs or 1.280ms

Vertical sync pulse 160µs

Pre and post equalizing pulse 5 pulse each

Sync pulse top 100%

Blanking/pedestal level 75%

Black level 72-75%

White level 10-12.5%

Width of video signal 5MHz

Chroma signal bandwidth -1.3MHz to +1.57MHz

Video IF 38.9MHz



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Audio IF 33.4MHz

Inter carrier frequency 5.5MHz

Audio modulation Frequency Modulation(FM)

Video modulation Amplitude Modulation (AM)

Total channel width in VHF 7MHz

Total channel width in UHF 8MHz

Q.6) Attempt any FOUR of the following: 16 marks

a) Draw frequency response of woofer, mid-range and tweeter, speakers. Write function of cross

over network.

(Frequency response curve-2 marks (even if curves drawn separately should be considered

and marks should be given and function of cross over network-2 marks)

Function of cross over network:

When a multi way loud speaker system is used to get flat frequency response for the entire

range of audio frequency, it is essential to have cross-over network to divide the incoming

signals in to separate frequencies ranges for each speaker.

Cross over network make use of the fact that the capacitive reactance decreases with

increase in frequency (XC=1/2ЛFC) and the inductive reactance increases with increase in

frequency (XL=2ЛFL).



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b) Explain additive mixing. (Diagram-2 marks brief explanation-2 marks)

In this type of mixing light from two or more colours obtained either from independent

sources or through filters can create a combines sensation of a different colour.

Secondary colours result when two primary colours of equal magnitude are additively

mixed. By pair wise additive mixing of colours the following complementary colours are

produced.

Red (30%) + Green (59%) =Yellow (89%)

Red (30%) + Blue (11%) = Magenta (41%) (purplish blue)

Blue (11%) + Green (59%) = Cyan (70%) (greenish blue)

Red (30%) + Green (59%) + Blue (11%) = White (100%) (luminance)

Additive mixing occurs when we see the light emitted by the sources.

c) Explain following terms in detail (explanation of hue-2 marks and explanation of

saturation-2 marks)

1) Hue: This is predominant spectral colour of the received light. Thus the colour of any object is

distinguished by its hue or tint.

Example: The green leaves have green hue and red tomatoes have red hue.

2) Saturation: This is the spectral purity of the colour light since single hue colours occur rarely

alone this indicates the amount of other colour present. A fully saturated colour has no white.

Example: A vivid green is fully saturated and when diluted by white it becomes light green.



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d) State the working principle of delta gun picture tube with diagram.

(Working principle-2 marks and digram-2 marks)

Working principle:

Electron beam from the three guns strikes three phosphor dots of s triad. The dots of red,

green and blue phosphor in a triad glow simultaneously, the intensity of glow being

proportional to the intensity of video signal of respective colours.

The eye adds the three colours emitted by the phosphor dots at a time and perceives the

resultant colour of the concerned pixel as in the original picture.

Triads glow one after other in quick succession due to deflection of the beams and hence

the whole picture is reproduces in its original colours.

The ratio of electrons passing through the holes to those reaching the shadow mask is only

about 20%. The remaining 80% of the total beam current energy is dissipated as a heat loss

in the shadow mask.



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f) Explain the functions of following components used for CD mechanism.

(Functions of CD lens- 2marks and functions of drive motor-2 marks) (Marks should be

given even if types of CD lens and drive motors are explained.)

Functions of CD lens:

In case of optical pick up assemble in CD the laser beam is emitted by laser diode for

purpose of detection. The lens and prism arrangement is used to direct the laser beam to

the CD surface and to direct the reflected laser beam towards photodiode array.

If the lens systems are not used them the laser beam may scatter in other direction and

hence proper detection will not take place.

Different types of lens used in CD players are

Collimation lens,

concave lens,

objective lens, and

Cylindrical lens.

Functions of Drive motors:

The drive motors in CD players are used for various purposes such as for loading and

unloading CD from tray, for rotating CD, for rotating laser beam etc.

The motor circuit consists of transistor or IC components within the drive components are

controlled by a PLL and servo processor.

Different types of motors used in CD players are:

tray loading or carriage motor,

slide sled feed motor and

Spindle, disc, turn table motor.

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