1 _CRT Display Design_

CRT Display Design
©2000 Display Laboratories Inc.
Session 1
Introduction

Featured Seminars
 Introduction to CRT Displays
 Video and Tube Biasing
 Deflection and High Voltage
 Micro-Control and Waveform Generators
 Special Topics and Miscellaneous Circuits

Introduction to CRT Displays
 Early development
 General description
 Block diagram
 Principles of operation
 Input signals
 Timing and resolutions
 Front of screen

General Description
 Cathode Ray Tubes use a fundamental method
for producing a light emitting image
 Two signals control X and Y location
 One to three signals control the intensity and or
color of the image
 Basically an analog device

Block Diagram (simplified)
Power Supply
Cathode Ray Tube
Deflection Amplifier
Video Amplifier
R
G
B
H
V

Principles of Operation
 Video Image Created by Vectored Beam
 Direct X-Y positioning of beam
 Video Image Created by Scanning Beam
 Left to Right and Top to Bottom Convention
 Progressive Scan, one frame per vertical

Image appears more stable on text
 Interlaced Scan, one field per vertical

Reduces video bandwidth, good for broadcast
 No fixed number of vectors, lines or pixels
defined

Video Display Components
 CRT Structures
 Shadow Mask & Purity
 Gun Design and use
 Color Perception
 X-Y Addressing Deflection
System
 Vertical Deflection Amplifier
 Horizontal Deflection
Amplifier
 Horizontal Linearity
 Horizontal ‘S’ correction
 Yoke
 Z Axis Video Control
 RGB Video Amplifiers
 Blanking Amplifier
 Operating Modes
 Other Services
 Focus Modulation
 Convergence Correction
 Sync. Processing
 Micro-Controller

Operating Modes
 Fixed Frequency
 Multi-Mode
 Multi-Sync
 Digital CRT Displays
 Timing and resolutions

Fixed Frequency
 Spot size set for ‘Merged Raster’.
 Geometry optimized at one frequency.
 Fixed horizontal and variable vertical rate.
 Fixed horizontal and vertical rates.
 Fewest parts and lowest in cost.

Multi-mode
 Designed to operate at predefined
Frequencies or pairs of frequencies.
 Few and fixed horizontal rates.
 Low in cost.
 Compatibility issues.
 Will not adapt to new modes without user
adjustment.

Multi-Sync
 Automatically sets reasonable raster size for
any in range signal.
 Can be factory preset for prime modes.
 User adjustable for new modes.
 Automatic or manual ‘save’ of settings.
 Micro-controller based.
 Higher in cost.

Digital CRT Display
 All digital video and sync. signals.
 Precise ‘Distortion Free’ image reproduction
under all conditions.
 Elimination of all ‘Arcane’ controls.
 Automatic adjustment of the rest.
 User adjustments free of interactive artifacts.
 Yet to be fully defined.
 Cost pending.

Input Signals
Typical sync on green input signal.

Input Signals
 RGB Video
 Separate Sync.
 Composite Sync.
Deflection Amplifier
Video Amplifier
R
G
B
H
V
Video Amplifier
R
G
B
H+V Sync.
Sepr.

Sync. Types
 Sync. on Video/Green
 Separate Sync.
 Composite 1 wire
 Separate 2 wire

Composite Sync. Types
 Serrations
 Half line
 Interlace
 Doubles
 Equalizing pulses
 Missing sync. pulses

Block Diagram
Power Supply
Cathode Ray Tube
Vertical & Horizontal
Deflection Amplifiers
Video Amplifier
& Blanking
R
G
B
H+V
Sync.
Sepr.
Focus and
Convergence

Future Seminars
 Video and Tube Biasing
 Deflection and High Voltage
 Micro-Control and Waveform Generators
 Special Topics and Miscellaneous Circuits

Video System
 Block diagram
 Preamp
 Input select
 Termination
 Contrast
 Sync Separator

Video System
 Sync tips
 Black level
 Back Porch Clamp
 Output Amp
 Cathode voltage swing
 T-rise/T-fall
 Cathode capacitance

Video System
 Beam current
 CRT Bias
 Cutoff
 Brightness
 Black level
 Arc suppression

Video System
 Color Tracking
 White balance
 Preset Temp
 Variable Temp
 White to Black color tint
 White uniformity
 Circuit considerations

Deflection System & High
Voltage
 Horizontal Deflection
 Vertical Deflection
 High Voltage

Vertical Deflection
 Block diagram
 Principles of fly-back scanning design
 Multi-scan considerations
 Frequency considerations
 Timing considerations
 Inductive load conditions
 Power dissipation

Horizontal Deflection
 Block diagram
 Principles of fly-back scanning design
 Multi-scan considerations
 Frequency considerations
 Timing considerations
 Horizontal drive conditions
 Conventional vs. separate deflection

High Voltage System
 Block diagram
 Fly-back
 Multiplier
 FBT construction and operating principles
 Static and dynamic regulation
 Beam current

Microprocessor & Jungle
 Micro-Controller
 AFC circuit
 Geometry correction principles
 Factory adjustment
 DPMS

Miscellaneous Circuits
 Digital convergence
 Focus (static and dynamic)
 Special Topics
 Single-sided board layout
 Jitter
 Beat noise
 EMI
 etc.

The Early Years
How We Got Into This Mess and
Those That Had a Part in It.

Early Development
Electro-Mechanical
 P. Nipkow First Proposed Scanning System
(Germany 1884)
 J. Baird First Transmittion of TV Image
(England 1925)
 J. Baird Field Sequential Color Demo
(England 1928)

Early Development
Electronic
 K. Braun Invented Cathode Ray Tube
(Germany 1897)
 V. Zworykin Demo of Crude Television
(USA 1923) for Westinghouse
 K. Takayanagi First Electronic Transmittion
(Tokyo 1926)
 P. Farnsworth Transmitted 60 Line Image
(USA 1927) of ‘$’
 A. Schroeder Simultaneous Color CRT
(USA 1946)

Paul Nipkow’s Camera
with mechanically scanned raster. Patented in 1884

John L. Baird’s Display
Based on the Nipkow disk, 1925

Karl Braun’s CRT
with electron scanned raster, Proposed in 1884

Vladimir Zworkin’s Camera
with electron scanned raster, 1929

Al Schroeder’s Color Tube
Simultaneous Color System, 1946
1/3

Proposed
Beam
Masking
Structure
2/3

Proposed
Mask and
Screen
Structure
end

Monochrome CRT
 Single
Beam
Electron
Gun
 One Color
Phosphor
 Simple
Vacuum
Tube

Paul Nipkow
 In 1884, university student Paul Nipkow of Germany
proposed and patented the world's first
electromechanical television system.
 Nipkow proposed a disc camera, that contained a disc
which was perforated. To capture a moving image the
disc was rotated before an image and had the effect of
dividing the picture into lines.
 Light sensitive selenium behind the perforated disk
would capture the moving image. The camera became
known as the Nipkow disk.
1/2

Paul Nipkow
 The Nipkow disk was a mechanical scanning system
and became the best known for its time. Nipkow
could not build a working system. He could not
amplify the electric current created by the selenium to
drive a receiver.
 It was not until 1907 and the development of an
amplification tube that serious development in
mechanical television would start.
2/2

John Logie Baird
 John Logie Baird, of Great Britain, has his place in
history as one of the champions of the development
of mechanical television. Known as an idea-rich
inventor, John Logie Baird was said to have had
trouble changing a fuses by himself, but had a flair for
publicity. Prior to his development efforts at television
he had failed at making artificial diamonds and had
attempted a cure for hemorrhoids that left him in
severe pain for a week.
1/3

John Logie Baird
 Despite his history on October 30, 1925, John Logie
Baird of London was successful in transmitting his first
picture: the head of a dummy. Looking for publicity he
visited the Daily Express newspaper to promote his
invention. The news editor was terrified. Later he was
quoted by one of his staff as saying:" For God's sake, go
down to reception and get rid of a lunatic who's down
there. He says he's got a machine for seeing by wireless!
Watch him-- he may have a razor on him."
 In 1928, Baird extended his system by transmitting a
signal between London and New York.
2/3

John Logie Baird
 In 1929 the British Broadcasting Service (BBC) adopted
the Baird mechanical system.
 By 1932 John Logie Baird had developed the first
commercially viable television system and had sold
10,000 sets.
 Baird's electromechanical system consisted of a light
sensitive camera behind a rotating disc. It delivered a
crude picture consisting of thirty lines at twelve frames
per second to a television receiver that displayed an
uneven and tiny orange and black image.
3/3

Vladimir Zworykin
 The person most often associated as the father of
television is Vladimir Zworykin.
 Teamed with David Sarnoff, Zworykin lead the
development at RCA of electronic television.
 Zworykin was cursed with living in interesting times,
born in Russia in 1889, he studied at the St.
Petersburg institute of technology.
 He was hired by one of his instructors, Boris Rosing,
who was seeking ways of extending mans vision.
1/10

Vladimir Zworykin
 By 1907 Rosing had developed a television system
which employed a mechanical disc system as a
camera and a glass tube (cathode ray tube) as a
receiver. The system was primitive but it was more
electronic than mechanical.
 With the Russian revolution, Rosing went into exile
and died.
 Zworykin carried on his work.
2/10

Vladimir Zworykin
 With the outbreak of world war I, Zworykin decided to
leave Russia for the United States.
 Zworykin found work at Westinghouse.
 Based on their pioneering efforts in radio, he tried to
convince them to do research in television. Turning
down an offer from Warner Brothers.
 Zworykin worked nights, fashioning his own crude
television system.
3/10

Vladimir Zworykin
 In 1923, Zworykin demonstrated his system before
officials at Westinghouse and applied for a patent.
 All future television systems would be based on
Zworykin's 1923 patent.
 Zworykin described his 1923 demonstration as
"scarcely impressive". Westinghouse officials were not
prepared to base an investment in television on such a
flimsy system.
 The company suggested that Zworykin devote his time
to more practical endeavors.
4/10

Vladimir Zworykin
 Undeterred, Zworykin continued in his off hours to
perfect his system. He was so persistent that the
laboratory guard was instructed to send him home a
2:00 in the morning if the lights of the laboratory were
still on.
 During this time, Zworykin managed to develop a
more sophisticated picture tube called the kinescope,
which serves as the basis for today's CRT display
tubes.
5/10

Vladimir Zworykin
 In 1929, Vladimir Zworykin invented the all electric
camera tube.
 Zworykin called his tube the iconoscope (literally "a
viewer of icons").
 He demonstrated both the iconoscope and kinescope
to IRE* the Institute of Radio Engineers. (*Now
known as IEEE.)
6/10

Vladimir Zworykin
 Zworykin's all electronic television system surpassed
the limitations of the mechanical television system.
 In attendance was David Sarnoff who eventually
hired Zworykin to develop his television system for
RCA.
 Under Sarnoff's watchful eye, Zworykin continued to
develop the electronic system.
7/10

Vladimir Zworykin
 When Zworykin started at RCA his system was
scanning 50 lines.
 Experimental broadcasts started in 1930 first using a
mechanical camera transmitting at 120 lines.
 By 1933 a complete electronic system was being
employed with a resolution of 240 lines.
8/10

Vladimir Zworykin
 Zworykin had originally told Sarnoff it would cost
$200,000 to develop a television system.
 The final cost was estimated to cost RCA about
$50,000,000.
9/10

Vladimir Zworykin
 RCA and Zworykin were not alone. By 1934 two
British electronic firms, EMI and Marconi, created an
all-electronic television system.
 They used the orthicon camera tube invented by an
American company, RCA.
 This electronic system was officially adopted by the
BBC in 1936. It consisted of 405 scanning lines,
changing at twenty five frames per second.
10/10

Kenjito Takayanagi
 The Japanese say the honor of the first working
electronic television system goes to Kenjito
Takayanagi of Tokyo.
 On Christmas Day, 1926, he used a cathode-ray tube
to display an image of Japanese writing.
 Japan now honors Mr. Takayanagi, as the inventor of
TV.
1/1

Philo T. Farnsworth
 In 1922, American Philo T. Farnsworth, who was then
a 15-year-old Idaho farm boy born in a log cabin,
described to his friends and teachers how an
electronic TV system might work.
 Later in 1927, he would transmit his first TV image
based on his system.
1/1

Cathode Ray Tube
 The CRT Display Monitor evolved from electronic
television which is based on the principal of the
cathode ray tube.
 Cathode Rays were first identified in 1859 by Julius
Plucker, a German mathematician and physicist.
 In 1878 William Crookes, a British chemist, confirmed
their existence by building a tube that displayed them.
1/3

Cathode Ray Tube
 Later , English physicist Ambrose Flemming, working
with Crookes tube, discovered that cathode rays
could be deflected and focused.This was
accomplished by wrapping the tube with wire and
creating a magnetic field by passing electric current
through the wire. A technique still used today.
2/3

Cathode Ray Tube
 In 1897, German physicist Karl Braun developed the
first cathode ray oscilloscope.
 Braun made the cathode rays visible by placing
fluorescent materials at the end of the tube.
 Braun built the oscilloscope to demonstrate how
cathode rays could be controlled by a magnetic field.
3/3

Chronology Of Television
Technology
 1817 - Swedish Baron Jons Berzelius isolates the
element selenium.
 1839 - Edmond Becquerel discovers the
electrochemical effects of light.
 1842 - Alexander Bain proposes facsimile telegraph
transmission that scans metal letters and reproduces
image by contact with chemical paper. Synchronized
scanning is part of proposed transmission system.
 1847 - F. Bakewell improves facsimile by creating
rotating scanning drums.

Technology
 1859 - German mathematician and physicist Julius
Plucker experiments with invisible cathode rays.
 1861 - Italian priest, Abbe Caselli, uses tin foil on
facsimile to transmit handwriting and pictures.
 MAY 1873 - British scientists, Willoughby Mith and
Joseph May noted that the electrical conductivity of
the element selenium changes when light falls on it.
This property, called photoconductivity, is used in
camera tubes.

Technology
 1878 - M. Senlacq proposes the use of selenium in
facsimile machines to transmit paper documents.
 1878 - Sir William Crookes develops a tube that
confirms the existence of cathode rays.
 1881 - British pioneer Shelford Bidwell demonstrates
his scanning photo telegraph that establishes both
scanning and the use of selenium in transmitting still
pictures.

Technology
 1884 - German scientist Paul Gottlieb Nipkow patented
a device for scene analysis that consisted of a rapidly
rotating disk placed between a scene and a light
sensitive selenium element. It became known as the
Nipkow disk. Although this was a mechanical design
(not in use today), it was the first television scanning
system, outlining the principle of scanning a moving
image. If the Nipkow disk was turned fast enough, it
theoretically created a scanning system capable of
showing a moving picture. It is believed a working
model was never built by Nipkow himself. It would take
the development of the amplification tube before the
Nipkow Disc would become practical.

Technology
 1888 - German physicist Wilhelm Hallwachs noted
that certain substances emit electrons when exposed
to light. Hallwachs demonstrated the possibility of
using photoelectric cells in cameras. This property
called photoemission was applied in the creation of
image orthicon tubes allowing the creation of the
electronic television camera.

Technology
 1897 - German Karl Braun invents the Cathode Ray
Tube (CRT).
 1904 - First color television system is proposed
based on the principle of scanning three primary
colors.
 1907 - American engineer Lee De Forest invented
the triode electron tube. This made amplification of
video signals created by photoconductivity and
photoemission possible.

Technology
 1907 - English inventor A.A. Campbell-Swinton and
Russian Boris Rosing independently suggested using a
cathode ray to reproduce the television picture on a
phosphorous coated screen. This suggested that the
electronic scanning system used in the CRT could
replace the mechanical Nipkow disk.
 1911 - English inventor A.A. Campbell-Swinton
proposed an electronic scanning system using a charge-
collecting screen and an electron gun to neutralize the
charge to create a varying current. The electronic
scanning system used in the CRT could then be adapted
as an electronic scanning system to replace the
mechanical Nipkow disk.

Technology
 1923 thru 1926 - American Charles F. Jenkins
developed a working television system based on the
Nipkow disk. In England, Scottish engineer John L.
Baird demonstrated a working television system that
was based on the Nipkow disk, with improved
resolution. The Baird system used infrared rays and
could take pictures in the dark. Both systems
produced a small crude orange and black
recognizable image.
 1923 - Westinghouse, General Electric, RCA, and
AT&T entered into television research.

Technology
 1923 - Vladimir K. Zworykin, a Russian immigrant to
the United States, patented the "iconoscope" an
electronic camera tube based on A.A. Campbell-
Swinton's proposal of 1911.
 1923 - Philo T. Farnsworth (13 years old) developed
an electronic camera tube, similar tube to Zworykin's
named the "kinescope".
 1926 - Canadian experiments with mechanical
television start in Montreal.
 1927 - First long distance television broadcast from
Washington to New York performed by AT&T.

Technology
 1928 - John L. Baird demonstrates a color television
system using a modified Nipkow disk.
 1928 - American inventor E. F. W. Alexanderson
demonstrates the first home television receiver in
Schenectady, New York. It consisted of a 3" screen
and delivered a poor and unsteady picture. On May
28, 1928 the first television station WGY began
broadcasting in Schenectady. Sets were built and
distributed by General Electric in Schenectady.

Technology
 1929 - John L. Baird starts transmissions using BBC
radio towers in off hours.
 1929 - Zworykin demonstrates the all electronic
television camera and receiver.
 1930 - American Philo Farnsworth patents electronic
television.
 1930 - NBC is granted an experimental broadcast
license.
 1931 - Television broadcasting starts in Canada by
CKAC of Montreal.

Technology
 1933 - 33 Radio Stations Are Broadcasting In
Canada.
 605 Radio Stations Are Broadcasting In United
States.
 8 Radio Stations Are Broadcasting In Newfoundland.
 1935 - Germany begins world's first public
broadcasting service.
 1935 - RCA pledges millions of dollars towards the
development of TV.

Technology
 1936 - Public broadcasting begins in England.
 1936 - Germany broadcasts Olympic Games.
 1939 - RCA displays TVs at World's Fair.
 1940 - American Peter Goldmark introduces a
refined color television system in New York City.
 1941 - NBC and CBS are granted commercial
broadcast licenses.

Technology
 1941 - United States adopts a 525 line black and
white system as the standard for broadcasting.
 1941 - A total of 400 television receivers had been
sold in the United States.
 1945 - There are an estimated 10,000 television sets
in the US.
 1946 - 6,500 television receivers are sold in the
United States.

Technology
 1947 - World Series (Baseball) is broadcasted,
attracting an audience in excess of four million in the
United States.
 1948 - CBS announces development of color
television system.
 1949 - NBC announces development of color
television system.
 1951 - Television broadcasting in color began and
ended in United States using the Peter Goldmark
color system that was not compatible with the 525
line black and white standard.

Technology
 1952 - CBC is licensed in Montreal and Toronto.
 1952 - Television sets in American homes pass the
22 million mark.
 1953 - Half the homes in the United States have
television sets.
 1953 - NTSC television standard is adopted in the
United States allowing for color television that is
compatible with existing black and white TV sets.

Technology
 1954 - Commercial color broadcasting begins in
United States using the NTSC standards.
 1955 - Videotape is introduced.
 1959 - CBC linked by microwave from Victoria to St.
Johns.
60 million mark.
 1961 - CTV receives television broadcast license.

Technology
 1962 - Telestar 1 satellite launched, thus opening
doors for television satellite transmission and allowing
intercontinental transmission when in proper position.
70 million mark.
 1965 - Commercial satellite Early Bird launched in
fixed orbit allowing continuous intercontinental
transmission.

Technology
 1965 - With only two exceptions, NBC announces all
prime time programs to be in color.
 1966 - Color television tests were conducted in
Canada.
 1967 - Canadian color television standards are set
and color transmission begins.
 1969 - Apollo 11 moonwalk is transmitted and
broadcast live from the moon.

Technology
 1974 - 97% of American homes have at least one
TV set and it is on at least five hours per day.
 1984 - Stereo television authorized.
 1987 - CBC shoots the world's first large scale
commercial HDTV production, "Chasing Rainbows".
 1990 - 1446 television stations broadcasting in
United States.

Shadow Mask
 This is a very popular technology. It is made up of
a screen laying just behind the phosphors.
 The electrons from three guns pass through the
mask at different angles to strike the desired
phosphor.

Aperture Grill
 This technology is used by Sony in Trinitron tubes
and Mitsubishi in Diamondtron tubes.
 The aperture grill consists of vertical wires.
 The mask has less metal, more of the electrons hit
the phosphor.

Aperture Grill
 The mask is flat and under tension in the vertical
direction.
 The phosphor is also placed in vertical stripes.
 A higher percentage of the area is covered by
phosphor.
 The result is a brighter picture & good color
saturation.
 Darker tinted glass can be used to give a higher
contrast ratio.

Slot Mask
 This technology is used by NEC under the trade
name “CromaClear”. It is a combination of Shadow
Mask and Aperture Grill technologies. The phosphor
dots are rectangular (tall and thin).
 This increases the phosphor area and reduces moiré
in the vertical direction. .

Flat Tension Mask
 Pioneered by Zenith and now manufactured by LG in
Korea.
 Perfectly flat face plate and mask.
 Mask is under tension on a flat frame.

Doming
 The shadow mask inside the CRT
is a thin sheet of steel or InVar
positioned about a half an inch
behind the phosphor screen.
 The shadow mask is susceptible
to thermal expansion.
 In areas of high beam current the
shadow mask will deform, shifting
the position of the holes or slots
in the shadow mask.
 Individual phosphor dot may be
spaced as little as .13 mm apart
(for a .22 mm dot pitch CRT).

Doming
 Very little movement in the
shadow mask will cause the
electron beam to strike the wrong
color phosphors.
 The result is poor color purity and
discoloration.
 InVar shadow masks can sustain
two to three times higher current
density than steel shadow masks
without noticeable problems. .
 Trinitrons and FTMs are resistant
to small area doming because the
wires are under tension. The
suspension components can still
expand result in color purity with
an overall bright picture.

Purity,4,6 Pole Magnets
 2 Pole, Purity
 4 Pole, Red-Blue
 6-Pole, Magenta-
Green

Purity Magnet
 The 2-Pole ‘Purity’ magnet is analogous with the
beam centering magnet on Monochrome Yokes.
 Its purpose is to move the beam/beams to the
‘optical’ center line of the deflection yoke.
 This will produce orthogonal vertical and horizontal
lines through the center of the faceplate and the best
overall balance of spot landing and purity.

Magnet Placement
 The purity magnet is placed
over a gap in the gun so all
three beams are affected.
 The 4 and 6 pole magnets
are placed over magnetic
shunt structures to optimize
their effect.
 The 4 and 6 pole magnets
may be used in combination
with dynamic correction
coils.

2-Pole Magnet Effect
Flux
Magnet
Movement
The ‘purity’ magnet can move all
beams in any direction together.

Magnetic shunt
Flux
Magnet
Movement

Degaussing
 The shadow mask or aperture grill must be made of
magnetic material! This leads to the need for
degaussing.
 The shadow mask and internal shielding hood form
a closed chamber where there is a near zero field.
 Degaussing is not to demagnetize the metal, but to
create a magnetization that compensates for the
earth's magnetic field.
 The sum of the two fields must be near zero.
 This theory was put forward by Philips in a recent
paper.

The Electron Gun (Mono-Chrome)
 The uni-potential gun can be broken down into
two sections, the triode and the lens section.
 The triode is the electron emitting and shaping
section formed by the electron source (cathode),
the control grid (G1) and the accelerator (G2).
 The lens of the uni-potential design has three
elements G3, G4 and G5.

The Triode
 A 6.3 or 12-volt filament heats the cathode.
Operating at an elevated temperature causes
electrons to "boil off" the surface of the cathode
and form a cloud.
 The electron-emitting surface of the cathode is
often impregnated with tungsten and barium to
lower the work function of the surface.
 The effective area of the cathode is determined by
the aperture size of G1 (first control grid).

The Triode
 The video signal is typically applied to the cathode
along with video blanking. This permits the G1 and
G2 elements to be biased relative to the cathode
for uniform operation from CRT to CRT.
 The physical relationship of G1, G2 and the
Cathode, influence the lower beam angle, center
focus voltage, and the spot size for a given gun
design.

The Triode
 Electrons carry a negative charge. They are
attracted to positive elements within the tube like
G2 and the faceplate (1st
and 2nd
anodes) and are
repelled by the relative negative charge of G1.
 The more negative G1 appears to the cathode,
the greater the reduction in the flow of electrons.

The Triode
 Beam current is attracted through a small hole in
G1, called the aperture by a positive voltage
applied to grid two (G2, the first accelerator or
anode).
 The bias voltage applied to G2 is set in
conjunction with G1 and Cathode to establish “cut-
off” of electron flow, at black levels in the picture.
 The bias voltage between the cathode (+) and G1
(-) has the largest influence on spot size after
physical gun design.

Triode Cross Section
Cathode
Heater
G1
G2
0 v -100v 500-800v
+30v-30v
+30v
0v

The Lens
 Electrostatic lenses are used to focus the electron
bean onto the phosphor screen in the front of the
tube.
 The combination of G3, G4, and G5 form the
lenses. G3 and G5 are connected to the fixed high
voltage of the anode (originally called the 2nd
anode).
 The voltage on G4 is varied to control the focal
distance. Static focus voltage and any dynamic
voltage if required are applied to G4 through the
base connector.

The Lens
 High-resolution displays require dynamic focus to
maintain pixel quality into the corners of the CRT.
This is even more critical on flat profile CRTs.
 Electron guns can be optimized for dynamic focus
or flat focus applications. A flat focus gun will
provide a compromise of focus quality from center
to edge and is appropriate for many low to
medium resolution applications.
 Displays requiring higher resolution such as those
in desktop publishing, graphics terminals,
document processing, and medical imaging,
require dynamic focus.

The Lens
 The function of each of these gun elements and
their interaction is critical to the overall
performance of the CRT.
 From cathode to the face of the CRT, it is the
relationship between each of these individual
elements that determines the final appearance of
the un-deflected spot in the center of the tube
face.

The Electron Gun (Color PIL)
 Example of Hitachi Elliptical Aperture,
Dynamic focus (A-EADF) Electron Gun

Hitachi Elliptical Aperture, Dynamic
focus (A-EADF) Electron Gun
 At the heart of Hitachi's high performance
monitors is the EADF electron gun which ensures
the sharp focus, high definition, distortion free
image.
 The elliptical aperture lenses produce maximum
focusing control while minimizing distortion effects
due to centerline offset.

Hitachi Elliptical Aperture, Dynamic
focus (A-EADF) Electron Gun
 Hitachi's dynamic focus capability means that
even FST screens have consistently sharp focus,
right into the corners where the beam path length
is substantially greater than at the center.
 An electro-static Quadra-pole lens which makes
constant adjustments to the cross sectional shape
of each beam ensures that the landing spot is
precisely circular whatever the deflection of the
beam or the position on the screen surface.

Beam Shape & Focus
 The electron beam leaving an electron gun will
normally be circular in shape. If the gun were at
the radius of curvature of the faceplate then the
spot at the faceplate would be round.
 The problem is that most CRTs are short, the gun
is very close to the faceplate.
 This causes the electron beam to strike the
phosphor at a non right angle.
 The corners will have an elliptical shaped spot-
landing pattern.

Beam Shape & Focus
 A Dynamic Quadra-pole Lens found in some
electron gun enables the beam to be made
elliptical as it leaves the gun. Naturally the
Quadra-pole lens will distort the beam in a
direction that is at a right angle to the normal
elliptical effect. The addition of the two elliptical
effects will result in a round but larger spot. The
beam’s spot shape, and therefore picture
sharpness, remain the same all over the screen.

Beam Shape & Focus
 Dynamic Focus voltages may be applied to the
gun of the CRT to optimize the spot size.
 A complex 3- D waveform is often needed on very
flat and/or large CRT’s.
 Several hundreds of volts of drive are used to
effect the beam at this point in the gun.
 The voltage may be different for the four corners of
the tube.

Thermionic Emission
 Thermionic emission is to electrons what
evaporation is to the water molecules in a hot cup
of coffee.
 It is a process by which some of the electrons
inside a piece of metal can 'boil away', leaving the
surface of the metal into the surrounding space.

Thermionic Emission
 Inside a metal the electrons are not stationary, but
are constantly moving, with an average speed that
is controlled by the temperature of the metal.
 It is important to realize that this is only the
average speed of the electrons, that some of them
will have speeds that are significantly larger than
this.
 It is these higher speeds, and therefore higher
energy electrons, which have enough energy to
escape from the metal.

Thermionic Emission
 Since the speed of the electrons increases with
temperature, the number of electrons with
sufficient energy to escape also increases with
temperature, in fact exponentially so.
 At room temperature (300 K) the number is very
small, but if the wire is heated to 1000K the
number of electrons escaping is dramatically
increased.

Color
 Colors are rays of light, i.e. electromagnetic waves
with wavelengths between 380 nm and 780 nm.
 We perceive them with our eyes and our brain
translates them into what we call "colors". In other
words: colors are products of our brain.
 This means that one person may perceive colors
slightly differently from another.

Color
 To display colors, monitors use what is called
"additive color mixing", using red, green and blue
light. If we mix red, green and blue light together, we
get white light.
 When white is required on the screen, three electron
guns hit the red, green and blue dots, or different
shapes, of phosphor that coat the inside of the
screen, which in turn glow together and produce
white light.

Color Metrics
 The idea of tri-receptor
vision was worked out far
before the physical
mechanism of retinal
pigments was
understood.
 A common diagram for
describing human color
perception was
developed by the
International
Commission on
Illumination (CIE).
 The CIE diagram is an
attempt to precisely
quantify the tri-receptor
nature of human vision.

Vertical Power Amplifier
 A vertical power amplifier is related to an audio power
amplifier.
 Audio amplifiers are voltage amplifiers (voltage in voltage
out).
 Vertical amplifiers are current amplifiers (voltage in current
out).
 Feedback comes from a current sensing point. This
is done because current is proportional to the amount
of deflection.

 Audio
amplifier
 Vertical
amplifier
B+
B-
B+
B-
Audio amplifier

 Low noise is critical.
 Open loop unity gain needs to extend to 1 - 10mhz.
 A small monitor may need only ± 0.5 amps p-p of
vertical yoke current using a 12 volt supply.
 Large color monitors may require ± 3 to 4 amps p-p
and use a 35 –50 volt supply during vertical trace and
70 –100 volts during retrace.

Voltage Doublers
 In order to obtain sufficiently short fly-back times, a
voltage greater than that required during scanning
must be applied to the yoke.
 During vertical retrace time a large voltage is
needed across the yoke to cause a fast retrace. A
voltage doubler boosts the positive supply voltage
only during vertical retrace.
 The vertical power amplifier can then run from a low
supply voltage when little output voltage is needed
and from a high supply voltage for the short time
that a high output voltage is needed. This results in
1/3 the power loss and 2 to 3 times faster retrace.

Voltage Doublers
 The top trace is the output voltage of the power
amplifier. The second trace is the supply voltage.

Anti-ringing Resistor
 Many power amplifiers have instability in the 1 to
3Mhz region. An anti-ringing resistor & capacitor
dampens out oscillations. See the manufacture’s
data sheet for proper values.
 Generally the resistor is in the 1 to 5 ohm range. It
is chosen to load down the amplifier at the
oscillation frequency. The time constant for the RC
is often in the .2 to 1uS range. The impedance of
the capacitor, at the oscillation frequency, should be
½ to ¼ that of the resistor.
 If the value of the capacitor is too large, the resistor
and amplifier will get hot.

Vertical Damping
 In many vertical amplifier designs a damping
resistor is placed across the yoke.
 One method to determine the resistor value is to
select a power resistor in the 100 to 500 ohm range
and adjust the value for best results.
 As can be seen, too large a value of resistance
leaves oscillation.
 Too small of a value slows the amplifier.

Vertical Damping
 The second method of determining the damping
resistor value involves knowing the power amplifier’s
gain/phase plot.
 The gain and phase of the resistors, capacitors and
yoke inductance must also be known and plotted on
the same graph. Watch for adequate gain and
phase margin.

Horizontal Wave Forms
 A horizontal deflection circuit
makes a saw tooth current
flow through a deflection coil.
 The current will have equal
amounts of positive and
negative current.
 The horizontal switch
transistor conducts for the
right hand side of the picture.
 The damper diode conducts
for the left side of the picture.
 Current only flows through the
fly back capacitor during
retrace time.

Horizontal Trace Right Side
 For time 1 the transistor is
turned on.
 Current ramps up in the yoke.
 The beam is moved from the
center of the picture to the
right edge.
 Energy is stored on the
inductance of the yoke.
 E=I2
L/2

Horizontal Retrace Right Side
 For time 2 the transistor is
turned off.
 Energy transfers from the
yoke to the fly-back capacitor.
 At the end of time two all the
energy from the yoke is
placed on the fly-back
capacitor.
 There is zero current in the
yoke and a large voltage on
the capacitor.
 The beam is quickly moved
from the right edge back to
the middle of the picture.

Horizontal Retrace Left Side
 During time 3 the energy on
the capacitor flows back into
the yoke.
 The voltage on the fly-back
capacitor decreases while the
current in the yoke builds until
there is no voltage on the
capacitor.
 By the end of time 3 the yoke
current is at it's maximum but
in the negative direction.
 The beam is quickly deflected
form the center to the left
edge.

 Time 4 represents the left hand
half of the picture.
 Yoke current is negative and
ramping down
 The beam moves from the left
to the center of the picture.
Horizontal Trace Left Side

Horizontal Linearity
 In the yoke current path there is a
saturable coil. Just like a size coil,
any inductance in series with the
yoke will reduce the size of the
picture.
 This saturable coil will change
inductance depending on the
amplitude and direction of current
flow.
 At the start of a trace the linearity
coil has an inductance of 20
percent of that of the yoke.
 By the center of the trace, the
linearity inductance has decreased
to about 4 percent of the yoke
where it remains for the rest of the
trace.
 Adjust this variable inductor so the
right and left sides of the picture
are the same size.
Voltage from two turns of wire added around the
linearity coil. When the coil saturates the voltage drops
to near zero

Horizontal Linearity
 Trace A is the yoke voltage at
about 1000 volts peak to
peak. Trace B is the yoke
current. Trace C is the
voltage across the total of all
resistance in the horizontal
loop. Trace D is the voltage
loss due to the
semiconductors in the loop.
Trace E is the voltage across
the S capacitor. Trace F is
the voltage across the
linearity coil.
 The linearity coil should have
a waveform like the inverse of
trace C+D. Thus the loss
seen in traces C+D+F should
equal a straight line.

Horizontal Losses
 Horizontal deflection
schematic to show losses
that cause linearity
problems.
 The ‘R. total’ is the
combination of deflection
yoke resistance +
resistance of the linearity
coil + resistance of any
size coil + yoke wires +
printed circuit traces +
ESR of the S-cap.

‘S’ Capacitor
 The ‘S’ capacitors corrects
outside versus center linearity
in the horizontal scan.
 The voltage on the ‘S’ cap has
a parabola plus the DC
horizontal supply.
 Reducing the value of ‘S’ cap
increases this parabola thus
reducing the size of the outside
characters and increasing the
size of the center characters.
 ‘S’ Capacitor value:
 Too low: picture will be
squashed towards edges.
 Too high: picture will be
stretched towards edges.

‘S’ Capacitor
 By simply putting a capacitor in
series with each coil, the saw-
tooth waveform is modified into
a slightly sine-wave shape.
 This reduces the scanning
speed near the edges where
the yoke is more sensitive.
 Generally the deflection angle
of the electron beam and the
yoke current are closely
related.
T?
Bsase Drive
C1
FlyBack cap
C2
S cap
D1
Damper Diode
Q1
H. Switch
DY
H. Yoke
T2
FlyBack Transformer
B+
L1
Size Coil

Deflection Angle .vs. ‘S’ Linearity
 In this example an electron
beam is deflected with nine
different current values.
(4,3,2,1,0,-1,-2,-3,-4 amps)
 A current in the range of 0 to 1
amp causes the beam to move
4cms.
 Current changing from 3 to 4
amps causes 6.5cm
movement.
 The yoke appears to be 1.5
times more sensitive at the
edge of the picture.
4
5
5.5
6.5
4
5
5.5
6.5

High Deflection Angles and Flat Tubes
 The amount of ‘S’ correction needed is related to the
flatness of the tube and the deflection angle.
 If the yoke is at the radius of the curvature of the tube
then no ‘S’ correction is needed.
 As the yoke is pushed toward the face of the tube
deflection angles get large.
 This problem is compounded on very flat tubes.

Inner Pin-cushion
 Many CRTs, especially flatter
ones, need geometry
correction that goes beyond
simple ‘S’ correction.
 Most tubes need inner pin-
cushion correction, which is
also called "dynamic ‘S’
correction".
 Some tubes need more ‘S’
correction only at the
extreme edges, this is called
"higher-order ‘S’ correction".

Yokes
 Saddle / Toroidal
 Saddle / Saddle
 Stator
 Pin Wound

Saddle / Toroidal
 Saddle horizontal
winding
 Toroidal vertical
winding
 Split core
 Inconsistent winding
control
 High leakage
 Low cost high
volume

Saddle / Saddle
 Great flexibility in
correcting geometry,
focus, and
convergence.
 Minimal radiation,
windings contained
within the ferrite
core.
 Reasonable
sensitivity.
 Medium cost High
volume

Stator
 Reliable and precise.
 The windings and
placed between the
slots in the ferrite.
 Consistent unit to unit
quality.
 Low inductance
windings.
 Good for Stroke
Displays.
 High cost low volume.

Pin Wound
 Pin Winding is a
technique developed to
precisely control
placement of wire in the
saddle.
 ‘Pins” are inserted in the
fixture as winding
progresses.
Can be used in any saddle
Precise like Stator Yoke

Stroke Display
 In the stroke character CRT the image is painted
by the electron beam.
 There is no raster.
 This type of CRT is often used for computer aided
design and other applications where line drawn
images are used.
 The effect is much like a pen plotter.

Scanned Rasters
 Two orthogonal electromagnet coils are used to
deflect the electron beam.
 One coil is used for horizontal positioning.
 The other for vertical position.
 Current through each coil determines position of
beam.
 They act like an optical lens.
 They are subject to similar distortions.

Raster Scan CRT
 Television sets and most computer monitors are
raster scanned.
 The electron beam scans the screen from left to
right and top to bottom to create a raster on the
screen.
 Characters are formed by changing the brightness
of dots at the required points on the raster.

Interlaced Rasters
 The next diagram shows an example of an interlaced
picture. The odd lines are scanned first omitting the
even lines. Then the even lines are scanned to
complete the picture frame.

Interlaced Pictures
 The benefit of an interlaced picture is that the
horizontal and video rate can be cut in half.
 This makes the video card in the computer much
easier to build.
 The video amplifier and the horizontal deflection
circuits in the monitor are also simplifier.
 An interlaced picture as used in television, works well
for pictures of flowers and trees or action shots.

Interlaced Pictures
 Generally an interlace picture is not excitable for
data terminals or application where the viewer is
close to the picture.
 An example of where interlace does not work well
is the letter "E". The vertical bar in the letter is
drawn both in the odd and even fields and thus
gets updated 60 times a second. The three
horizontal lines in the letter "E" reside in the odd
field and only get drawn 30 times a second. This
makes the right side of the "E" flicker.

Focus and Convergence
 Focus and Convergence are interrelated.
 Adjusting for optimal focus and spot size
exaggerates the visibility of poor convergence.
 Often focus is sacrificed for convergence.

Convergence
 Poor convergence is often
thought to be just bad focus by
the uninformed.
 Black characters on a light or
white background can suffer from
contrast loss and color fringing.
 Very high density display formats
obviously need excellent
convergence.
 Low resolution displays will show
the greatest improvement to
image quality because they
suffer from the poorest
convergence control.

Dynamic Focus
 All monitors have the
ability to set a focus
voltage. The voltage is
DC and will be the same
for all areas of the
picture.
 The Top Focus control
sets the focus voltage for
the top and bottom of the
picture. Adding a ‘1D’
dynamic vertical
correction.

Dynamic Focus
 The Side Focus sets the
focus voltages along the
side of the picture. Often
called Horizontal Focus
Modulation. This can be
a ‘1D’ or ‘2D’ modulation.
 When both top and side
focus voltages are
adjusted the focus
voltage is a complex
‘2D’ or ‘3D’ waveform
containing horizontal and
vertical frequencies.

Horizontal Focus
 The horizontal focus voltage is a parabola at the horizontal
frequency.
 The typical place to get this waveform is from the ‘S’ capacitor.
 The amount of side focus voltage varies from tube to tube.
 A variable gain amplifier is used to set the amount of H. focus
voltage needed.
 A power amplifier boosts the parabola to about 50-volts.
 A transformer multiplies the 50-volt signal to several hundred
volts.

Dynamic Convergence
 Dynamic convergence has many of the same waveform
requirements as focus.
 Horizontal convergence has a ‘S’ shape leaning from left to
right, and reverses polarity from top to bottom.
 ‘Natural’ functions can compensate but not totally correct
convergence.
 High order distortions occur due to the variable mechanical
construction and assembly of tube and yoke.
 Dynamic waveform generation, coil drivers and neck
components are needed for dynamic correction.
 Digital CRT solutions may eliminate coils and drivers by
applying correction in a frame buffer.

(C) Copyright Display Labs 1996192
Correction Waveform
Measurements
Tile Correction Waveform Measurements.

(C) Copyright Display Labs 1996193
Correction Waveform
Measurements
Tile Correction Waveform Measurements.

VESA Monitor Timing
Specifications Version
1.0 Rev. 0.8
Standards and Guidelines
Summary

Standards and Guidelines
Summary

Moiré
 At low resolution there will be no moiré effect. Each
pixel may extend over several holes in the shadow
mask. As the resolution goes up the number of
pixels may approach the number of shadow mask
holes. Individual pixels no longer cover enough
phosphor dots to ensure that they are constant
brightness or constant color. The average of all the
pixels in an area will still be expectable.

Moiré
 Moiré appears as wavy lines, contour lines, or light
and dark bands often seen in areas of constant
brightness. These may be very fine or 2 cm large
and changing across the screen. Tubes with good
focus will have worse moiré.

Moiré
 There are two sources of moiré. Video moiré is
caused by the video pattern (horizontally) verses
the dot pitch. Raster moiré is the spacing of scan
lines verses the dot pitch. Trinitrons, which do not
have a vertical dot structure should not have
interference of this sort from the raster lines will
have interference from the horizontal pixel
structure.

Moiré
 You can test for moiré by slowly adjusting the
vertical size and horizontal size. If it is moiré, you
should see the pattern change in location and
frequency. Changes to vertical and horizontal
position will change the moiré patterns very little.
They will not remain locked to the moving image.
 Some monitors have a Moiré control or switch.
Generally this control causes every other picture to
be moved very slightly. Generally the movement is
0 to .5 pixels. A similar effect is to slightly de-focus
the picture.

Moiré
 An example of large beam with fine shadow mask.

Moiré
 An example of a beam that is 4% different than the
mask size.

1 _CRT Display Design_

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