pctechguide.com

  • Home
  • Guides
  • Tutorials
  • Articles
  • Reviews
  • Glossary
  • Contact

The Anatomy of a CRT Monitor (and CRT TVs)

Most CRT monitors have case depths about as deep as the screen is wide, begging the question what is it that’s inside a monitor that requires as much space as a PC’s system case itself?

A CRT is essentially an oddly-shaped, sealed glass bottle with no air inside. It begins with a slim neck and tapers outward until it forms a large base. The base is the monitor’s screen and is coated on the inside with a matrix of thousands of tiny phosphor dots. Phosphors are chemicals which emit light when excited by a stream of electrons: different phosphors emit different coloured light. Each dot consists of three blobs of coloured phosphor: one red, one green, one blue. These groups of three phosphors make up what is known as a single pixel.

CRT

In the bottle neck of the CRT is the electron gun, which is composed of a cathode, heat source and focusing elements. Colour monitors have three separate electron guns, one for each phosphor colour. Images are created when electrons, fired from the electron guns, converge to strike their respective phosphor blobs.

Convergence is the ability of the three electron beams to come together at a single spot on the surface of the CRT. Precise convergence is necessary as CRT displays work on the principal of additive coloration, whereby combination of different intensities of red green and blue phosphors create the illusion of millions of colours. When each of the primary colours are added in equal amounts they will form a white spot, while the absence of any colour creates a black spot. Misconvergence shows up as shadows which appear around text and graphic images.

The electron gun radiates electrons when the heater is hot enough to liberate electrons (negatively charged) from the cathode. In order for the electrons to reach the phosphor, they have first to pass through the monitor’s focusing elements. While the radiated electron beam will be circular in the middle of the screen, it has a tendency to become elliptical as it spreads its outer areas, creating a distorted image in a process referred to as astigmatism. The focusing elements are set up in such a way as to initially focus the electron flow into a very thin beam and then – having corrected for astigmatism – in a specific direction. This is how the electron beam lights up a specific phosphor dot, the electrons being drawn toward the phosphor dots by a powerful, positively charged anode, located near the screen.

Electron

The deflection yoke around the neck of the CRT creates a magnetic field which controls the direction of the electron beams, guiding them to strike the proper position on the screen. This starts in the top left corner (as viewed from the front) and flashes on and off as it moves across the row, or raster, from left to right. When it reaches the edge of the screen, it stops and moves down to the next line. Its motion from right to left is called horizontal retrace and is timed to coincide with the horizontal blanking interval so that the retrace lines will be invisible. The beam repeats this process until all lines on the screen are traced, at which point it moves from the bottom to the top of the screen – during the vertical retrace interval – ready to display the next screen image.

Since the surface of a CRT is not truly spherical, the beams which have to travel to the centre of the display are foreshortened, while those that travel to the corners of the display are comparatively longer. This means that the period of time beams are subjected to magnetic deflection varies, according to their direction. To compensate, CRT’s have a deflection circuit which dynamically varies the deflection current depending on the position that the electron beam should strike the CRT surface.

Before the electron beam strikes the phosphor dots, it travels thorough a perforated sheet located directly in front of the phosphor. Originally known as a shadow mask, these sheets are now available in a number of forms, designed to suit the various CRT tube technologies that have emerged over the years. They perform a number of important functions:

  • they mask the electron beam, forming a smaller, more rounded point that can strike individual phosphor dots cleanly
  • they filter out stray electrons, thereby minimising overspill and ensuring that only the intended phosphors are hit
  • by guiding the electrons to the correct phosphor colours, they permit independent control of brightness of the monitor’s three primary colours.

Shadow

When the beam impinges on the front of the screen, the energetic electrons collide with the phosphors that correlate to the pixels of the image that’s to be created on the screen. When this happens each is illuminated, to a greater or lesser extent, and light is emitted in the colour of the individual phosphor blobs. Their proximity causes the human eye to perceive the combination as a single coloured pixel.

  • Flat Panel & LCD Monitors
  • The Anatomy of a CRT Monitor (and CRT TVs)
  • CRT Monitor Resolution and Refresh Rates (VSF)
  • Monitor Interlacing
  • What is the Dot Pitch of a Computer Monitor
  • Dot Trio Monitors
  • Grill Aperture Monitors
  • Monitor Technologies: Slotted Mask
  • Enhanced Dot Pitch Monitors
  • Electron Beam Monitors
  • Monitor Controls
  • The Different Types of CRT Monitors – From ShortNeck to FST
  • What is a Digital CRT Monitor and How Does It Work
  • What is LightFrame Technology?
  • Safety Standards For Computer Monitors
  • TCO Monitor Standards
  • Monitor Ergonomics

Share this:

  • Click to share on Twitter (Opens in new window)
  • Click to share on Facebook (Opens in new window)

Related

Filed Under: CRT Monitors

Latest Articles

Cyrix MediaGX

The introduction of the MediaGX processor in February 1997 defined the first new PC architecture in a decade, and ignited a new market category - the low-cost Basic PC. The growth of this market proved to be been explosive, and Cyrix's … [Read More...]

Hard Disk (hard drive) Operation

The disc platters are mounted on a single spindle that spins at a typical 10,000rpm. On EIDE and SCSI drives the disk controller is part of the drive itself. It controls the drive's servo-motors and translates the fluctuating voltages from the head into digital data for the CPU. Data is … [Read More...]

HDCP Technology

High-Bandwidth Digital Content Protection is effectively a copy protection scheme designed to eliminate the possibility of intercepting digital data midstream between the source to the display. Using hardware on both the graphics adapter card and the monitor, HDCP will encrypt … [Read More...]

2021 PC Hardware Releases to Bolster Your Gaming

If you are a PC gamer, then chances are you are looking to upgrade your kit over the coming year. However, a lot of money can go into building the … [Read More...]

New Transfer Feature in Dropbox Enable Sharing files with Third Parties

Dropbox has been a popular P2P sharing platform for many years. They don't announce new features as often as other applications, since they have a … [Read More...]

Ransomware Operators Find Data Theft Profitable

How valuable is your data? That’s not a question that organizations or individuals have to ask themselves all that often. You might know the market … [Read More...]

Engineers Encounter the Quantum Challenge with Computers Running a Hundred Million Times Faster

Quantum computers have been a subject of discussion for many years. They have probably been something that philosophers and technology pundits have … [Read More...]

Transferring Image Files from Your Cell Phone Without Cables or Email

You don't have a cable available to transfer the photos from your cell phone to your computer? You don't feel comfortable sending them through your … [Read More...]

Why Drupal Accessibility is Vital for Your Website

Drupal may not be as popular as WordPress, but it is still used in over 1 million websites. The Internet might be more conducive to our needs if more … [Read More...]

Guides

  • Computer Communications
  • Mobile Computing
  • PC Components
  • PC Data Storage
  • PC Input-Output
  • PC Multimedia
  • Processors (CPUs)

Recent Posts

Disk Maintenance – The Disk Defrag

When most people want to purchase a new computer or upgrade their current one, they focus on finding a CPU with the quickest speed, the most computing … [Read More...]

Core i7 2nd Gen

The Core i7 2nd Gen is an example of innovative engineering. Gone are the days when you had to depend on individual plug in cards to avail the … [Read More...]

Pentium D

The advent of the multicore desktop processor is expected to end the clock rate race between Intel and AMD which has … [Read More...]

[footer_backtotop]

Copyright © 2021 About | Privacy | Contact Information | Wrtie For Us | Disclaimer | Copyright License | Authors