CRT TV Report

CRT TV Report

1. G. H. Raisoni College of Engineering
An Autonomous Institution under UGC Act 1965 |Accredited by NBA & NAAC ‘A’ Grade

DEPARTMENT
OF
ELECTRONICS AND TELECOMMUNICATION
ENGINEERING
(2015-2016)

TAE-1
“Activity Based Learning”

Subject:
Television Engineering
“CRT”

Year/Semester:
3
rdyear / 5
th semester.
Section: ‘C ’.

Guided By:
Prof. K.A. Kalbande
Submitted by:
Roll No. 28. Ankush Fulambarkar

2. Report
On
Digital TV Set Top Box

Introduction:-
The cathode ray tube (CRT) is a vacuum tube containing one or more electron guns, and
a fluorescent screen used to view images.
[1]
It has a means to accelerate and deflect the
electron beam(s) onto the screen to create the images. The images may represent
electrical waveforms(oscilloscope), pictures ( television, computer
monitor), radar targets or others. CRTs have also been used as memory devices, in
which case the visible light emitted from the fluorescent material (if any) is not
intended to have significant meaning to a visual observer (though the visible pattern on
the tube face may cryptically represent the stored data).

The CRT uses an evacuated glass envelope which is large, deep (i.e. long from front
screen face to rear end), fairly heavy, and relatively fragile. As a matter of safety, the
face is typically made of thick lead glass so as to be highly shatter-resistant and to block
most X-ray emissions, particularly if the CRT is used in a consumer product.
CRTs have largely been superseded by newer display technologies such as LCD, plasma
display, and OLED, which have lower manufacturing costs, power consumption, weight
and bulk.
The vacuum level inside the tube is high vacuum on the order of 0.01 Pa
[2]
to 133 nPa.
[3]

In television sets and computer monitors, the entire front area of the tube is scanned
repetitively and systematically in a fixed pattern called a raster. An image is produced

3. by controlling the intensity of each of the three electron beams, one for each additive
primary color (red, green, and blue) with a video signal as a reference.
[4]
In all modern
CRT monitors and televisions, the beams are bent by magnetic deflection, a varying
magnetic field generated by coils and driven by electronic circuits around the neck of
the tube, although electrostatic deflection is commonly used in oscilloscopes, a type of
diagnostic instrument.

History:
Cathode rays were discovered by Johann Hittorf in 1869 in primitive Crookes tubes. He
observed that some unknown rays were emitted from thecathode (negative electrode)
which could cast shadows on the glowing wall of the tube, indicating the rays were
traveling in straight lines. Artur Shusterdemonstrated cathode rays could be deflected
by electric fields, and William Crookes showed they could be deflected by magnetic
fields. In 1897, J. J. Thompson succeeded in measuring the mass of cathode rays,
showing that they consisted of negatively charged particles smaller than atoms, the first
"subatomic particles", which were later named electrons. The earliest version of the CRT
was known as the "Braun tube", invented by the German physicist Ferdinand Braun in
1897.
[5][6]
It was a cold-cathode diode, a modification of the Crookes tube with
a phosphor-coated screen.
In 1907, Russian scientist Boris Rosing used a CRT in the receiving end of an
experimental video signal to form a picture. He managed to display simple geometric
shapes onto the screen, which marked the first time that CRT technology was used for
what is now known as television.
[1]

The first cathode ray tube to use a hot cathode was developed by John B. Johnson (who
gave his name to the term Johnson noise) and Harry Weiner Weinhart of Western
Electric, and became a commercial product in 1922.
It was named by inventor Vladimir K. Zworykin in 1929.
[7]
RCA was granted a
trademark for the term (for its cathode ray tube) in 1932; it voluntarily released the
term to the public domain in 1950.
[8]

The first commercially made electronic television sets with cathode ray tubes were manufactured
by Telefunken in Germany in 1934.
Colour CRT:-
Color tubes use three different phosphors which emit red, green, and blue light
respectively. They are packed together in stripes (as in aperture grille designs) or
clusters called "triads" (as in shadow mask CRTs).
[18]
Color CRTs have three electron
guns, one for each primary color, arranged either in a straight line or in anequilateral
triangular configuration (the guns are usually constructed as a single unit). (The
triangular configuration is often called "delta-gun", based on its relation to the shape of
the Greek letter delta.) A grille or mask absorbs the electrons that would otherwise hit
the wrong phosphor.
[19]
A shadow mask tube uses a metal plate with tiny holes, placed
so that the electron beam only illuminates the correct phosphors on the face of the

4. tube;
[18]
the holes are tapered so that the electrons that strike the inside of any hole will
be reflected back, if they are not absorbed (e.g. due to local charge accumulation),
instead of bouncing through the hole to strike a random (wrong) spot on the screen.
Another type of color CRT uses an aperture grille of tensioned vertical wires to achieve
the same result.


Block Diagram:-

Introduction to Amplifiers
An amplifier is used to increase the amplitude of a signal waveform, without changing other
parameters of the waveform such as frequency or wave shape. They are one of the most
commonly used circuits in electronics and perform a variety of functions in a great many electronic
systems.
Fig 1.0.1 Amplifier general symbol, used in system diagrams
The general symbol for an amplifier is shown in Fig 1.0.1. The symbol gives no detail of the type of
amplifier described, but the direction of signal flow can be assumed (as flowing from left to right of
the diagram). Amplifiers of different types are also often described in system or block diagrams by
name.

5. Amplifiers as Parts of Large Electronic Systems
For example look at the block diagram of an analogue TV receiver in Fig 1.0.2 and see how many
of the individual stages (shaded green) that make up the TV are amplifiers. Also notice that the
names indicate the type of amplifier used. In some cases the blocks shown are true amplifiers and
in others, the amplifier has extra components to modify the basic amplifier design for a special
purpose. This method of using relatively simple, individual electronic circuits as "building blocks" to
create large complex circuits is common to all electronic systems; even computers and
microprocessors are made up of millions of logic gates, which are simply specialised types of
amplifiers. Therefore to recognise and understand basic circuits such as amplifiers is an essential
step in learning about electronics.
A.F. Amplifiers
Audio frequency amplifiers are used to amplify signals in the range of human hearing,
approximately 20Hz to 20kHz, although some Hi-Fi audio amplifiers extend this range up to around
100kHz, whilst other audio amplifiers may restrict the high frequency limit to 15kHz or less.Audio
voltage amplifiers are used to amplify the low level signals from microphones, tape and disk
pickups etc. With extra circuitry they also perform functions such as tone correction equalisation of
signal levels and mixing from different inputs, they generally have high voltage gain and medium to
high output resistance.
Audio power amplifiers are used to receive the amplified input from a series of voltage amplifiers,
and then provide sufficient power to drive loudspeakers.
I.F. Amplifiers
Intermediate Frequency amplifiers are tuned amplifiers used in radio, TV and radar. Their purpose
is to provide the majority of the voltage amplification of a radio, TV or radar signal, before the audio
or video information carried by the signal is separated (demodulated) from the radio signal. They
operate at a frequency lower than that of the received radio signal, but higher than the audio or
video signals eventually produced by the system. The frequency at which I.F. amplifiers operate
and the bandwidth of the amplifier depends on the type of equipment. For example, in AM radio
receivers the I.F. amplifiers operate at around 470kHz and their bandwidth is normally 10kHz (465
kHz to 475kHz), while TV commonly uses 6Mhz bandwidth for the I.F. signal at around 30 to
40MHz, and in radar a band width of 10 MHz may be used.
R.F. Amplifiers

6. Fig. 1.0.3 FM Radio using AF, IF and RF amplifiers.
Radio Frequency amplifiers are tuned amplifiers in which the frequency of operation is governed by
a tuned circuit. This circuit may or may not, be adjustable depending on the purpose of the
amplifier. Bandwidth also depends on use and may be relatively wide, or narrow. Input resistance
is generally low, as is gain. (Some RF amplifiers have little or no gain at all but are primarily a
buffer between a receiving antenna and later circuitry to prevent any high level unwanted signals
from the receiver circuits reaching the antenna, where it could be re-transmitted as interference). A
special feature of RF amplifiers where they are used in the earliest stages of a receiver is low noise
performance. It is important that background noise generally produced by any electronic device, is
kept to a minimum because the amplifier will be handling very low amplitude signals from the
antenna (µV or smaller). For this reason it is common to see low noise FET transistors used in
these stages.
Ultrasonic Amplifiers
Ultrasonic amplifiers are a type of audio amplifier handling frequencies from around 20kHz up to
about 100kHz; they are usually designed for specific purposes such as ultrasonic cleaning, metal
fatigue detection, ultrasound scanning, remote control systems etc. Each type will operate over a
fairly narrow band of frequencies within the ultrasonic range.
Wideband Amplifiers
Wideband amplifiers must have a constant gain from DC to several tens of MHz. They are used in
measuring equipment such as oscilloscopes etc. where there is a need to accurately measure
signals over a wide range of frequencies. Because of their extremely wide bandwidth, gain is low.
DC Amplifiers
DC amplifiers are used to amplify DC (0Hz) voltages or very low frequency signals where the DC
level of the signal is important. They are common in many electrical control systems and measuring
instruments.
Video Amplifiers
Video amplifiers are a special type of wide band amplifier that also preserve the DC level of the
signal and are used specifically for signals that are to be applied to CRTs or other video equipment.
The video signal carries all the picture information in TV, video and radar systems. The bandwidth
of video amplifiers depends on use. In TV receivers it extends from 0Hz (DC) to 6MHz and is wider
still in radar.Buffer Amplifiers
Buffer amplifiers are a commonly encountered, specialised amplifier type that can be found within
any of the above categories, they are placed between two other circuits to prevent the operation of
one circuit affecting the operation of the other. (They ISOLATE the circuits from each other). Often
buffer amplifiers have a gain of one, i.e. they do not actually amplify, so that their output is the

7. same amplitude as their input, but buffer amplifiers have a very high input impedance and a low
output impedance and can therefore be used as an impedance matching device. This ensures that
signals are not attenuated between circuits, as happens when a circuit with a high output
impedance feeds a signal directly to another circuit having a low input impedance.
Operational Amplifiers

Operational amplifiers (Op−amps) have developed from circuits designed for the early analogue
computers where they were used for mathematical operations such as adding and subtracting.
Today they are widely used in integrated circuit form where they are available in single or multiple
amplifier packages and often incorporated into complex integrated circuits for specific applications.
The design is based on a differential amplifier, which has two inputs instead of one, and produces
an output that is proportional to the difference between the two inputs. Without negative feedback,
op amps have an extremely high gain, typically in the hundreds of thousands. Applying negative
feedback increases the op amp´s bandwidth so they can operate as wideband amplifiers with a
bandwidth in the MHz range, but reduces their gain. A simple resistor network can apply such
feedback externally and other external networks can vary the function of op−amps
R.F. Amplifiers

Fig. 1.0.3 FM Radio using AF, IF and RF amplifiers.
Radio Frequency amplifiers are tuned amplifiers in which the frequency of operation is governed by
a tuned circuit. This circuit may or may not, be adjustable depending on the purpose of the
amplifier. Bandwidth also depends on use and may be relatively wide, or narrow. Input resistance
is generally low, as is gain. (Some RF amplifiers have little or no gain at all but are primarily a
buffer between a receiving antenna and later circuitry to prevent any high level unwanted signals
from the receiver circuits reaching the antenna, where it could be re-transmitted as interference). A
special feature of RF amplifiers where they are used in the earliest stages of a receiver is low noise
performance. It is important that background noise generally produced by any electronic device, is
kept to a minimum because the amplifier will be handling very low amplitude signals from the
antenna (µV or smaller). For this reason it is common to see low noise FET transistors used in
these stages.

8. Ultrasonic Amplifiers
Ultrasonic amplifiers are a type of audio amplifier handling frequencies from around 20kHz up to
about 100kHz; they are usually designed for specific purposes such as ultrasonic cleaning, metal
fatigue detection, ultrasound scanning, remote control systems etc. Each type will operate over a
fairly narrow band of frequencies within the ultrasonic range.
Wideband Amplifiers
Wideband amplifiers must have a constant gain from DC to several tens of MHz. They are used in
measuring equipment such as oscilloscopes etc. where there is a need to accurately measure
signals over a wide range of frequencies. Because of their extremely wide bandwidth, gain is low.
DC Amplifiers
DC amplifiers are used to amplify DC (0Hz) voltages or very low frequency signals where the DC
level of the signal is important. They are common in many electrical control systems and measuring
instruments.
Video Amplifiers
Video amplifiers are a special type of wide band amplifier that also preserve the DC level of the
signal and are used specifically for signals that are to be applied to CRTs or other video equipment.
The video signal carries all the picture information in TV, video and radar systems. The bandwidth
of video amplifiers depends on use. In TV receivers it extends from 0Hz (DC) to 6MHz and is wider
still in radar.







Reference:-
1. www.google.com
2. https://en.wikipedia.org/wiki/
3. http://www.learnabout-electronics.org/Amplifiers/amplifiers10.php