Most of us spend a lot of time in front of our monitors, Let us know what is inside a computer monitor. Starting with basics.
- Monitor is the output device of the computer.
- Now- a- days they are called as I-O devices, because both input and output devices are connected together and are dependent on each other.
- Whatever information is accepted from the keyboard is also reflected on the monitor and the results obtained after processing are also seen on the monitor.
- Monitors are also called as Cathode Ray Tube (CRT) terminals, or Visual Display Unit.
- The Cathode Ray Tube (CRT) terminal or CRT monitors consists of an important component called picture tube or CRT.
- This is connected to a video controller electronic circuit in the computer that supervises the operation of displaying the output or pictures on the display screen.
- The CRT display device displays information as dots or picture elements (pixels) on the screen as it receives the information signals as video signals from the computer.
- This device consists of an evacuated conical glass tube with phosphor coated on the inner front surface called screen.
The tube consists of the following:
- Electron source
- Control Grid
- Accelerating anode
- Vertical deflection plates
- Horizontal deflection plates
- Interior metal coating
- Screen with phosphor coating.
- The electron source is a component inside the tube which consists of a heating filament and an oxide coated cathode.
- This unit is a source of electrons.
- The cathode is heated by a heating filament to emit a large number of electrons.
- These electrons come to the control grid.
- The control grid is applied a positive voltage, which accelerates the electrons.
- The control grid actually decides the number of electrons which are to strike the phosphor coated screen.
- If the grid is applied a negative voltage, then no electrons will be allowed to pass the grid and hence the screen will be blanked.
- If a large positive voltage is applied to the grid, then the grid attracts many electrons which will be striking the screen.
- This in turn will increase the intensity of the emitted light when the beam strikes the phosphor coated screen.
- Thus the intensity of the beam can be controlled by the voltage applied to the grid.
- The electrons accelerated by the grid are again accelerated by an accelerating anode.
- The accelerating anode is applied with a positive voltage.
- A focussing electron lens assembly focuses the electron beam which passes through the hole of the cylindrical metal enclosure.
- This assembly of the electron source, control grid and the accelerating anode with focussing system is known as the Electron Gun.
Vertical deflection plates:
- The beam from the electron gun passes through a pair of vertical deflection plates.
- The beam can be moved up by applying a positive voltage of the first plate, and can be moved down by applying voltage to the second plate.
- The beam can thus be made to trace a line along the Y-direction or vertically, by controlling the voltage applied to the vertical deflection plates.
Horizontal deflection plates:
- After the vertical deflection plates, the electron beam passes through a pair of horizontal deflection plates.
- If the positive voltage is applied to the left plate, the beam will move left along the horizontal direction and moves right if a positive voltage is applied to the right plate.
- Now the beam can be moved horizontally along X-direction by controlling the voltage applied to the horizontal deflections.
- These deflection plates are placed in the neck of the conical glass tube.
Interior metal coating:
Now the electron beam to reach the phosphor coated screen is further accelerated by applying a high positive voltage to a metallic coating inside the sides of the conical part of the cathode ray tube.
Screen with phosphor coating:
- This focussed and accelerated electron beam now hits the phosphor coated screen at one point.
- This point lights up.
- The colour of the light depends upon the type of phosphor used.
- Phosphor P1 & P4 emit white light, P7 and P31 emit green light which are normally used in computer graphic displays.
The CRT display screen consists of picture elements or pixels as a matrix of columns and rows. The character to be displayed is considered as made of dots put on to screen, with different display parameters like colour code, blinking intensity etc. The number of dots or picture elements or pixels is referred to as resolution.